Charles P Gerba

Interests

Research

Pollution Science; environmental fate and transport of pathogens in the environment; quantitative microbial risk assessment; assessment and development of new disinfectants; fate and transport of pathogens in the subsurface.

Teaching

Pollution Science; environmental fate and transport of pathogens in the environment; quantitative microbial risk assessment

Courses

Scholarly Contributions

Books

• Haas, C. N., Rose, J. R., & Gerba, C. P. (2014). Quantiative Microbial Risk Assessment. New York: John Siley.
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  Test-book for teaching of course in Quantitative Microbial Risk Assessment
• Matthews, K. R., Gerba, C. P., & Sapers, G. M. (2014). The Produce Contamination Problem, 2nd edition. New York: Elsevier.
• Pepper, I. L., Gerba, C. P., & Gentry, T. (2014). Enviromental Micobiology 3rd Edition. New York: Academic Press.

Chapters

• Gerba, C. P. (2022). . Predicted and measured virucidal efficacies of microbicides for emerging and re-emerging viruses associated with WHO priority diseases. In Disinfection of Viruses(pp 65-92). London: IntechOpen.
• Gerba, C. P. (2022). Antivirus coatings as continuously active disinfectants. In Disinfection of Viruses(pp 53-64). London, UK: IntchOpen.
• Gerba, C. P., & Ikner, L. (2021). Antiviral Coatings as Continuously Active Disinfectants. In Disinfection of Viruses. Intechopen. doi:DOI: 10.5772/intechopen.101752
• Gerba, C. P., & Ikner, L. A. (2021). Antiviral Coatings as Continuously Active Disinfectants. In Disinfection of Viruses.
• Gerba, C. P., Gerba, C. P., Rock, C. M., Rock, C. M., Mclain, J. E., & Mclain, J. E. (2017). Environmental antibiotic resistance associated with land application of biosolids. In Antimicrobial Resistance in Wastewater Treatment Processes. Hoboken, NJ: Wiley-Blackwell.
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  Land application of biosolids derived from wastewater treatment processes has been increasing throughout the world, with more than 6.0 dry tons of biosolids now applied on an annual basis in the U.S. alone. For this reason, biosolids application has been proposed as a key point source for introducing antimicrobial resistant organisms, genetic elements of antimicrobial resistance, and antibiotic compounds as contaminants into agricultural soils. Recent studies cover a range of implications of land application of biosolids, with some studies suggesting minimal increased risk for development of antibiotic resistance, while other studies indicate significantly enhanced resistance development. It is becoming increasingly clear that results are dependent on composting treatments, land application methods and timing, and soil conditions prior to biosolids application. This chapter will present recent research examining the potential for transfer of antibiotic resistance from the wastewater treatment plant to the surrounding environment via biosolids application, with special emphasis on biosolids treatment and application methods that may enhance or reduce the presence of resistance determinants. The potential human health risk arising from transfer of resistance to agricultural soils will also be discussed.
• Ikner, l., & Gerba, C. P. (2017). Adenoviruses. In International Encyclopedia of Public Health. Second edition(pp 5-9).
• Mclain, J. E., Rock, C. M., & Gerba, C. P. (2018). Environmental antibiotic resistance associated with land application of biosolids. In Antimicrobial Resistance in Wastewater Treatment Processes. Hoboken, NJ: Wiley-Blackwell.
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  Land application of biosolids derived from wastewater treatment processes has been increasing throughout the world, with more than 6.0 dry tons of biosolids now applied on an annual basis in the U.S. alone. For this reason, biosolids application has been proposed as a key point source for introducing antimicrobial resistant organisms, genetic elements of antimicrobial resistance, and antibiotic compounds as contaminants into agricultural soils. Recent studies cover a range of implications of land application of biosolids, with some studies suggesting minimal increased risk for development of antibiotic resistance, while other studies indicate significantly enhanced resistance development. It is becoming increasingly clear that results are dependent on composting treatments, land application methods and timing, and soil conditions prior to biosolids application. This chapter will present recent research examining the potential for transfer of antibiotic resistance from the wastewater treatment plant to the surrounding environment via biosolids application, with special emphasis on biosolids treatment and application methods that may enhance or reduce the presence of resistance determinants. The potential human health risk arising from transfer of resistance to agricultural soils will also be discussed.
• Gerba, C. P. (2016). Adenoviruses. In International Encyclopedia of Public Health. Second edition.. Amsterdam.: Elsevier.
• Gerba, C. P. (2016). Extraction and purification of viral nucleic acids from environmental samples.. In Sample Preparation Techniques for Soil, Plant and Animal Samples(pp 315-324). new York: Springer.
• Gerba, C. P. (2016). Food Virology: Advances and needs. In Viruses in Foods(pp 1-5). Amsterdam: Elsevier.
• Gerba, C. P. (2016). Managed aquifer recharge systems for natural and sustainable wastewater reclamation and reuse technology: Health concerns associated with human viruses. In Safe use of Wastewater in Agriculture: Good Practice Examples(pp 3-20). Dresden, Germany: UNU-Flores.
• Gerba, C. P., & Nichols, G. (2015). Water-based disease and microbial growth. In Routledge Handbook of Water and Health(pp 52-70). New York: Routledge.
• Gerba, C. P., Kitajima, M., & Haramoto, E. (2014). Salivirus/Klassevirus: an emerging virus associated with pediatric diarrhea/acute flaccid paralysis and environmental contamination. In Influenza and RNA Viruses(pp 111-122). New York: Nova Science.
• Gerba, C. P. (2013). Occurrence and transmission of food- and waterborne viruses by fomites. In Viruses in food and water: risks, surveillence and control(pp 203-216). Cambridge, UK: Woodhead Publishing.
• Gerba, C. P. (2013). Silver as a disinfectant. In Encyclopedia of Metalloproteins(pp 2009-2013). New York: Springer.
• Gerba, C. P. (2013). Titanium dioxide as a disinfectant. In Encyclopedia of Metalloproteins(pp 2241-2247). New York: Springer.
• Gerba, C. P. (2013). Viral presence in waste water and sewge and control methods. In Viruses in food and water: risks, surveillence and control(pp 293-315). Cambridge, UK: Woodhead Publishing.
• Gerba, C. P., & Rock, C. (2014). Water quality. In The Produce Contamination Problem. 2nd ed(pp 123-138). New York: Elsevier.
• Marciano-Cabral, F., MacLean, R. C., Bright, K. R., Sarkar, P., Blair, B. L., & Gerba, C. P. (2009). Chapter 19 - Occurrence and control of Naegleria fowleri in drinking water wells. In Giardia and Cryptosporidium: From Molecules to Disease.(pp 238-247). Cambridge, MA: CAB International.
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  Naegleria fowleri is a water-based protozoan found naturally in soil and warm waters. Thedeaths of two children due to N. fowleri in the Phoenix, AZ, metropolitan area occurredin 2002, and the drinking water obtained from groundwater was found to be the sourceof the exposure. A survey was conducted of municipal drinking water wells in central andsouthern Arizona. N. fowleri was identified in 11 of 143 wells tested. The calculated Ct(chlorine concentration × time) for N. fowleri cysts by free chlorine was 31 for a 99%reduction at room temperature, pH 7.5 and trophozoites 6. Chlorination can be used tocontrol N. fowleri transmission via drinking water with appropriate guidance related toproper dosages and contact times.

Journals/Publications

• Foster, A. R., Haas, C. N., Gerba, C. P., & Pepper, I. L. (2024). Effectiveness of monochloramine for inactivation of coronavirus in reclaimed water. The Science of the total environment, 906, 167634.
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  Fecal shedding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by infected persons into wastewater was documented early during the COVID-19 pandemic, thereby stimulating inquiries into the effectiveness of municipal wastewater treatment processes for the reduction of infectious viruses. In wastewater treatment plants, free chlorine has traditionally been the disinfectant utilized due to its low cost and high efficacy. However, regulations limiting disinfection by-products have prompted a shift to chloramination in many areas of the United States. While studies regarding the effectiveness of free chlorine against many viral agents are abundant, the efficacy of monochloramine (NHCl) has been less well researched. This study aimed to determine the effectiveness of pre-formed monochloramine for disinfection of human coronavirus 229E (HCoV-229E) in both phosphate-buffered saline (PBS) and reclaimed water from a water reclamation plant in Tucson, Arizona. Reclaimed water was sampled over the course of six months (August 2020 to November 2020), and dosed with monochloramine at 3 mg/L. An additional 1 mg/L free ammonia was added to simulate the operational conditions of the treatment plant. Viability was determined using MRC-5 host cell monolayers, using the TCID assay method. An average Ct (concentration of disinfectant multiplied by the contact time to achieve a 99.9 % reduction of the target organism) of 176 mg*min/L monochloramine was determined. No significant difference in inactivation rate was observed between the dosed reclaimed water and phosphate buffered saline (PBS). These data indicate that monochloramine is an effective disinfectant for coronaviruses. They also indicate that the water matrix type did not significantly impact the disinfection efficacy of monochloramine against HCoV-229E in reclaimed wastewater compared to PBS.
• Kahn, D., Chen, W., Linden, Y., Corbeil, K. A., Lowry, S., Higham, C. A., Mendez, K. S., Burch, P., DiFondi, T., Verhougstraete, M., De Roos, A. J., Haas, C. N., Gerba, C., & Hamilton, K. A. (2024). A microbial risk assessor's guide to Valley Fever (Coccidioides spp.): Case study and review of risk factors. The Science of the total environment, 917, 170141.
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  Valley Fever is a respiratory disease caused by inhalation of arthroconidia, a type of spore produced by fungi within the genus Coccidioides spp. which are found in dry, hot ecosystems of the Western Hemisphere. A quantitative microbial risk assessment (QMRA) for the disease has not yet been performed due to a lack of dose-response models and a scarcity of quantitative occurrence data from environmental samples. A literature review was performed to gather data on experimental animal dosing studies, environmental occurrence, human disease outbreaks, and meteorological associations. As a result, a risk framework is presented with information for parameterizing QMRA models for Coccidioides spp., with eight new dose-response models proposed. A probabilistic QMRA was conducted for a Southwestern US agricultural case study, evaluating eight scenarios related to farming occupational exposures. Median daily workday risks for developing severe Valley Fever ranged from 2.53 × 10 (planting by hand while wearing an N95 facemask) to 1.33 × 10 (machine harvesting while not wearing a facemask). The literature review and QMRA synthesis confirmed that exposure to aerosolized arthroconidia has the potential to result in high attack rates but highlighted that the mechanistic relationships between environmental conditions and disease remain poorly understood. Recommendations for Valley Fever risk assessment research needs in order to reduce disease risks are discussed, including interventions for farmers.
• Boone, S. A., Ijaz, M. K., Bright, K. R., Silva-Beltran, N. P., Nims, R. W., McKinney, J., & Gerba, C. P. (2023). Antiviral Natural Products, Their Mechanisms of Action and Potential Applications as Sanitizers and Disinfectants. Food and environmental virology, 15(4), 265-280.
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  Plant extracts, natural products and plant oils contain natural virucidal actives that can be used to replace active ingredients in commercial sanitizers and disinfectants. This review focuses on the virucidal mechanisms of natural substances that may exhibit potential for indoor air and fomite disinfection. Review of scientific studies indicates: (1) most natural product studies use crude extracts and do not isolate or identify exact active antiviral substances; (2) many natural product studies contain unclear explanations of virucidal mechanisms of action; (3) natural product evaluations of virucidal activity should include methods that validate efficacy under standardized disinfectant testing procedures (e.g., carrier tests on applicable surfaces or activity against aerosolized viruses, etc.). The development of natural product disinfectants requires a better understanding of the mechanisms of action (MOA), chemical profiles, compound specificities, activity spectra, and the chemical formulations required for maximum activity. Combinations of natural antiviral substances and possibly the addition of synthetic compounds might be needed to increase inactivation of a broader spectrum of viruses, thereby providing the required efficacy for surface and air disinfection.
• Gerba, C. P. (2023). Transfer efficiency of an enveloped virus, human coronavirus 229E, from various hard surface fomites to finger pads of the hands. Infect. Contr. Hosp. Epidemology, 44, 335-337. doi:https://doi.org/10.1017/ice.2021.428
• Gerba, C. P., Ikner, L. A., Leija, B., Gundy, P., & Rutala, W. (2023). Transfer efficiency of an enveloped virus, human coronavirus 229E, from various hard surface fomites to finger pads of the hands. Infection Control & Hospital Epidemiology.
• Goforth, M. P., Boone, S. A., Clark, J., Valenzuela, P. B., McKinney, J., Ijaz, M. K., & Gerba, C. P. (2023). Impacts of lid closure during toilet flushing and of toilet bowl cleaning on viral contamination of surfaces in United States restrooms. American journal of infection control.
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  Viral aerosols generated during toilet flushing represent a potential route of pathogen transmission. The goal of this study was to determine the impact of toilet lid closure prior to flushing on the generation of viral aerosols and cross-contamination of restroom fomites.
• González-Gómez, J. P., Lozano-Aguirre, L. F., Medrano-Félix, J. A., Chaidez, C., Gerba, C. P., Betancourt, W. Q., & Castro-Del Campo, N. (2023). Evaluation of nuclear and mitochondrial phylogenetics for the subtyping of Cyclospora cayetanensis. Parasitology research, 122(11), 2641-2650.
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  Cyclospora cayetanensis is an enteric coccidian parasite responsible for gastrointestinal disease transmitted through contaminated food and water. It has been documented in several countries, mostly with low-socioeconomic levels, although major outbreaks have hit developed countries. Detection methods based on oocyst morphology, staining, and molecular testing have been developed. However, the current MLST panel offers an opportunity for enhancement, as amplification of all molecular markers remains unfeasible in the majority of samples. This study aims to address this challenge by evaluating two approaches for analyzing the genetic diversity of C. cayetanensis and identifying reliable markers for subtyping: core homologous genes and mitochondrial genome analysis. A pangenome was constructed using 36 complete genomes of C. cayetanensis, and a haplotype network and phylogenetic analysis were conducted using 33 mitochondrial genomes. Through the analysis of the pangenome, 47 potential markers were identified, emphasizing the need for more sequence data to achieve comprehensive characterization. Additionally, the analysis of mitochondrial genomes revealed 19 single-nucleotide variations that can serve as characteristic markers for subtyping this parasite. These findings not only contribute to the selection of molecular markers for C. cayetanensis subtyping, but they also drive the knowledge toward the potential development of a comprehensive genotyping method for this parasite.
• Jung, Y., Abney, S. E., Reynolds, K. A., Gerba, C. P., & Wilson, A. M. (2023). Evaluating infection risks and importance of hand hygiene during the household laundry process using a quantitative microbial risk assessment approach. American journal of infection control, 51(12), 1377-1383.
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  Contaminated laundry contributes to infectious disease spread in residential and home health care settings. The objectives were to (1) evaluate pathogen transmission risks for individuals doing laundry, and (2) compare hand hygiene timing to reduce risks.
• Sherchan, S. P., Thakali, O., Ikner, L. A., Gerba, C., & Haramoto, E. (2023). Survivability of Delta and Omicron variants of SARS-CoV-2 in wastewater. Water research, 246, 120644.
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  Concerns of fecal-aerosol transmission of coronavirus disease 2019 (COVID-2019) coupled with increased transmissibility and disease severity of Delta and Omicron variants of concern (VOC) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), suggest studies on survival of VOC in wastewater are warranted. To the best of our knowledge, this is the first study to investigate the survivability of Delta and Omicron VOC in filtered and unfiltered raw wastewater, and secondary effluent at room temperature (23 °C). The time required for 90 % inactivation (T) of Delta and Omicron VOC in unfiltered raw wastewater was calculated as 17.7 and 15.3 h, respectively. Rapid inactivation of VOC in wastewater and inability to isolate SARS-CoV-2 in wastewater suggest risks from fecal-aerosol transmission are low. Nevertheless, high transmissibility of VOC cautions overruling fecal-aerosol transmission of COVID-19. Future studies on survival of SARS-CoV-2 in wastewater should attempt viral culture by spiking feces collected from COVID-19 infected patients into wastewater to match the real-world scenario.
• Sherchan, S., Ikner, L. A., & Gerba, C. P. (2023). Inactivation of SARS-CoV-2 in Water by Chlorination. Food and environmental virology, 15(3), 262-264.
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  Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is present in both respiratory secretions and feces, creating its potential for transmission by swimming pools. Recreational water activity is known to be at increased risk of respiratory infections and respiratory viruses have caused been detected and have caused outbreaks in swimming pools. However, little is known regarding the chlorine inactivation of SARS-CoV-2 in water typical of swimming pools in the USA. In this study, the inactivation of SARS-CoV-2 Isolate hCoV-19/USA-WA1/2020 was observed in water by chlorination. All experiments were conducted within a BSL-3 laboratory at room temperature. Our results show that the virus was reduced by 3.5 log (> 99.9%) after 30 s of 2.05-mg/L free chlorine contact and greater than 4.17 log (limit of detection) (> 99.99%) within 2 min.
• Sherchan, S., Thakali, O., Ikner, L. A., & Gerba, C. P. (2023). Survival of SARS-CoV-2 in wastewater. The Science of the total environment, 882, 163049.
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  The ongoing pandemic of Coronavirus disease 2019 (COVID-19) has affected >600 million people with >6 million deaths. Although Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2), the etiologic agent of COVID-19, is transmitted via respiratory droplets or direct contact, isolation of viable SARS-CoV-2 in feces has been reported. Therefore, there is a need for understanding the persistence of SARS-CoV-2 and emerging variants in wastewater. In this study, the survival of SARS-CoV-2 isolate hCoV-19/USA-WA1/2020 was observed in three wastewater matrices - filtered and unfiltered raw wastewater, and secondary effluent. All experiments were conducted within a BSL-3 laboratory at room temperature. The time required for inactivation of 90 % (T) of SARS-CoV-2 was 10.4, 10.8, and 18.3 h for unfiltered raw, filtered raw, and secondary effluent, respectively. Progressive decline in infectivity of the virus following first order kinetics was noted in these wastewater matrices. To the best of our knowledge, this is the first study to describe the survival of SARS-CoV-2 in secondary effluent.
• Zhiteneva, V., Mosher, J., Gerba, C. P., Rauch-Williams, T., & Drewes, J. E. (2023). A new workflow for assigning removal credits to assess overall performance of managed aquifer recharge (MAR). Water research, 235, 119836.
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  Pathogen removal in managed aquifer recharge (MAR) systems is dependent upon numerous operational, physicochemical water quality, and biological parameters. Due to the site-specific conditions affecting these parameters, guidelines for specifying pathogen removal have historically taken rather precautionary and conservative approaches in order to protect groundwater quality and public health. A literature review of regulated pathogens in MAR applications was conducted and compared to up-and-coming indicators and surrogates for pathogen assessment, all of which can be gathered into a toolbox from which regulators and operators alike can select appropriate pathogens for monitoring and optimization of MAR practices. Combined with improved knowledge of pathogen fate and transport obtained through lab- and pilot-scale studies and supported by modeling, this foundation can be used to select appropriate, site-specific pathogens for regarding a more efficient pathogen retention, ultimately protecting public health and reducing costs. This paper outlines a new 10 step-wise workflow for moving towards determining robust removal credits for pathogens based on risk management principles. This approach is tailored to local conditions while reducing overly conservative regulatory restrictions or insufficient safety contingencies. The workflow is intended to help enable the full potential of MAR as more planned water reuse systems are implemented in the coming years.
• Abney, S. E., Wilson, A. M., Ijaz, M. K., McKinney, J., Reynolds, K. A., & Gerba, C. P. (2022). Minding the matrix: The importance of inoculum suspensions on finger transfer efficiency of virus. Journal of applied microbiology, 133(5), 3083-3093.
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  The aim of this study was to determine how the transfer efficiency of MS-2 coliphage from the toilet seat to hands and fingertip to lip differs according to the suspension of the inoculum.
• Gerba, C. P. (2022). . Entrainment of E. coli and Listeria montocytogenes from sediment in irrigation canal. . International Journal of Sediment Reserch, 37, 701-714.
• Gerba, C. P. (2022). An application of relating Legionella water monitoring results to estimate health outcomes. Water Reserch.
• Gerba, C. P. (2022). Control of viral and bacterial contamination of lettuce by subsurface drip irrigation. Journal of Irrigation and Drainage Engineering. doi:DOI:10.1061/(ASCE)IR.1943-4774.0001706.
• Gerba, C. P. (2022). Occurrence of enteric viruses and fecal indicators in submarine groundwater discharges in the coastal environment of the Mexican Caribbean. Water Environment. doi:doi:10.1111/wej.12815.
• Gerba, C. P. (2022). Quantifying pathogen infection risks from household laundry practices. Journal of Applied Microbiology, 132, 1435-1448.
• Gerba, C. P. (2022). Resuspension and attachment of phix174 in sediment flow. Journal of Environmental engineering. doi:DOI:10.1061/(ASCE)EE.1943-78700.0001996.
• Gerba, C. P., Reynolds, K. A., McKinney, J., Ijaz, M. K., Wilson, A. M., & Abney, S. E. (2022). Minding the matrix: The importance of inoculum suspensions in finger transfer efficiency. Journal of Applied Microbiology.
• Khalid Ijaz, M., Nims, R. W., McKinney, J., & Gerba, C. P. (2022). Virucidal efficacy of laundry sanitizers against SARS-CoV-2 and other coronaviruses and influenza viruses. Scientific reports, 12(1), 5247.
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  The clothes laundering process affords numerous opportunities for dissemination of infectious virus from contaminated clothing to appliance surfaces and other household surfaces and eventually to launderer's hands. We have explored the efficacy of laundry sanitizers for inactivating coronaviruses and influenza viruses. Virucidal efficacy was tested using standardized suspension inactivation methods (EN 14476) or hard-surface inactivation methods (ASTM E1053-20) against SARS-CoV-2, human coronavirus 229E (HCoV 229E), influenza A virus (2009-H1N1 A/Mexico), or influenza B virus (B/Hong Kong). Efficacy was measured in terms of log reduction in infectious virus titer, after 15 min contact time (suspension studies) or 5 min contact time (hard surface studies) at 20 ± 1 °C. In liquid suspension studies, laundry sanitizers containing p-chloro-m-xylenol (PCMX) or quaternary ammonium compounds (QAC) caused complete inactivation (≥ 4 log) of HCoV 229E and SARS-CoV-2 within 15 min contact time at 20 ± 1 °C. In hard surface studies, complete inactivation (≥ 4 log) of each coronavirus or influenza virus, including SARS-CoV-2, was observed following a 5-min contact time at 20 ± 1 °C. Respiratory viruses may remain infectious on clothing/fabrics and environmental surfaces for hours to days. The use of a laundry sanitizer containing microbicidal actives may afford mitigation of the risk of contamination of surfaces during handling of the laundry and washing appliances (i.e., washer/dryer or basin), adjacent surfaces, the waste water stream, and the hands of individuals handling clothes contaminated with SARS-CoV-2, influenza viruses, or other emerging enveloped viruses.
• Ma, B., Bright, K., Ikner, L., Ley, C., Seyedi, S., Gerba, C. P., Sobsey, M. D., Piper, P., & Linden, K. G. (2022). UV Inactivation of Common Pathogens and Surrogates Under 222 nm Irradiation from KrCl* Excimer Lamps. Photochemistry and photobiology.
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  Germicidal ultraviolet (UV) devices have been widely used for pathogen disinfection in water, air, and on food and surfaces. Emerging UV technologies, like the krypton chloride (KrCl*) excimer emitting at 222 nm, are rapidly gaining popularity due to their minimal adverse effects on skin and eyes compared with conventional UV lamps emitting at 254 nm, opening opportunities for UV disinfection in occupied public spaces. In this study, inactivation of seven bacteria and five viruses, including waterborne, foodborne and respiratory pathogens, was determined in a thin-film aqueous solution using a filtered KrCl* excimer emitting primarily at 222 nm. Our results show that the KrCl* excimer can effectively inactivate all tested bacteria and viruses, with most microorganisms achieving more than 4-log (99.99%) reduction with a UV dose of 10 mJ cm . Compared with conventional UV lamps, the KrCl* excimer lamp exhibited better disinfection performance for viruses but was slightly less effective for bacteria. The relationships between UV sensitivities at 222 and 254 nm for bacteria and viruses were evaluated using regression analysis, resulting in factors that could be used to estimate the KrCl* excimer disinfection performance from well-documented UV kinetics using conventional 254 nm UV lamps. This study provides fundamental information for pathogen disinfection when employing KrCl* excimers.
• Malayil, L., Ramachandran, P., Chattopadhyay, S., Allard, S. M., Bui, A., Butron, J., Callahan, M. T., Craddock, H. A., Murray, R., East, C., Sharma, M., Kniel, K., Micallef, S., Hashem, F., Gerba, C. P., Ravishankar, S., Parveen, S., May, E., Handy, E., , Kulkarni, P., et al. (2022). Variations in Bacterial Communities and Antibiotic Resistance Genes Across Diverse Recycled and Surface Water Irrigation Sources in the Mid-Atlantic and Southwest United States: A CONSERVE Two-Year Field Study. Environmental science & technology, 56(21), 15019-15033.
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  Reduced availability of agricultural water has spurred increased interest in using recycled irrigation water for U.S. food crop production. However, there are significant knowledge gaps concerning the microbiological quality of these water sources. To address these gaps, we used 16S rRNA gene and metagenomic sequencing to characterize taxonomic and functional variations (e.g., antimicrobial resistance) in bacterial communities across diverse recycled and surface water irrigation sources. We collected 1 L water samples ( = 410) between 2016 and 2018 from the Mid-Atlantic (12 sites) and Southwest (10 sites) U.S. Samples were filtered, and DNA was extracted. The V3-V4 regions of the 16S rRNA gene were then PCR amplified and sequenced. Metagenomic sequencing was also performed to characterize antibiotic, metal, and biocide resistance genes. Bacterial alpha and beta diversities were significantly different ( < 0.001) across water types and seasons. Pathogenic bacteria, such as , , and were observed across sample types. The most common antibiotic resistance genes identified coded against macrolides/lincosamides/streptogramins, aminoglycosides, rifampin and elfamycins, and their read counts fluctuated across seasons. We also observed multi-metal and multi-biocide resistance across all water types. To our knowledge, this is the most comprehensive longitudinal study to date of U.S. recycled water and surface water used for irrigation. Our findings improve understanding of the potential differences in the risk of exposure to bacterial pathogens and antibiotic resistance genes originating from diverse irrigation water sources across seasons and U.S. regions.
• Silva-Beltrán, N. P., Galvéz-Ruíz, J. C., Ikner, L. A., Umsza-Guez, M. A., de Paula Castro, T. L., & Gerba, C. P. (2022). In vitro antiviral effect of Mexican and Brazilian propolis and phenolic compounds against human coronavirus 229E. International journal of environmental health research, 1-13.
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  Propolis is a resinous substance collected by bees (). It is used for its biological properties. This natural product is available as a safe therapeutic option. Herein, we report the antiviral effects of brown propolis extract from Mexico and green and red propolis extracts from Brazil, as well as their phenolic compounds (quercetin, caffeic acid, and rutin) in preventing infection of MRC-5 cells by HCoV-229E. Normal human fibroblast lung cells (MRC-5) were used to determine the cytotoxicity of the compounds. All samples studied showed antiviral activity. Green and brown propolis extracts, and quercetin exhibited the best EC values with values of 19.080, 11.240, and 77.208 µg/mL against HCoV-229E, respectively, and with TC of 62.19, 29.192, and 298 µg/mL on MRC-5 cells, respectively. These results are the first in vitro study of the effects of propolis on HCoV-229E and provide the basis for the development of natural formulations against other coronavirus strains.
• Wilson, A. M., Canter, K., Abney, S. E., Gerba, C. P., Myers, E. R., Hanlin, J., & Reynolds, K. A. (2022). An application for relating Legionella shower water monitoring results to estimated health outcomes. Water research, 221, 118812.
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  Exposure models are useful tools for relating environmental monitoring data to expected health outcomes. The objective of this study was to (1) compare two Legionella shower exposure models, and (2) develop a risk calculator tool for relating environmental monitoring data to estimated Legionella infection risks and Legionnaires' Disease (LD) illness risks. Legionella infection risks for a single shower event were compared using two shower Legionella exposure models. These models varied in their description of partitioning of Legionella in aerosols and aerosol deposition in the lung, where Model 1 had larger and fewer aerosol ranges than Model 2. Model 2 described conventional vs. water efficient showers separately, while Model 1 described exposure for an unspecified shower type (did not describe it as conventional or water efficient). A Monte Carlo approach was used to account for variability and uncertainty in these aerosolization and deposition parameters, Legionella concentrations, and the dose-response parameter. Methods for relating infection risks to illness risks accounting for demographic differences were used to inform the risk calculator web application ("app"). Model 2 consistently estimated higher infection risks than Model 1 for the same Legionella concentration in water and estimated deposited doses with less variability. For a 7.8-min shower with a Legionella concentration of 0.1 CFU/mL, the average infection risks estimated using Model 2 were 4.8 × 10 (SD=3.0 × 10) (conventional shower) and 2.3 × 10 (SD=1.7 × 10) (water efficient). Average infection risk estimated by Model 1 was 1.1 × 10 (SD=9.7 × 10). Model 2 was used for app development due to more conservative risk estimates and less variability in estimated dose. While multiple Legionella shower models are available for quantitative microbial risk assessments (QMRAs), they may yield notably different infection risks for the same environmental microbial concentration. Model comparisons will inform decisions regarding their integration with risk assessment tools. The development of risk calculator tools for relating environmental microbiology data to infection risks will increase the impact of exposure models for informing water treatment decisions and achieving risk targets.
• Abney, S. E., Ijaz, M. K., McKinney, J., & Gerba, C. P. (2021). Laundry Hygiene and Odor Control: State of the Science. Applied and environmental microbiology, 87(14), e0300220.
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  Laundering of textiles-clothing, linens, and cleaning cloths-functionally removes dirt and bodily fluids, which prevents the transmission of and reexposure to pathogens as well as providing odor control. Thus, proper laundering is key to controlling microbes that cause illness and produce odors. The practice of laundering varies from region to region and is influenced by culture and resources. This review aims to define laundering as a series of steps that influence the exposure of the person processing the laundry to pathogens, with respect to the removal and control of pathogens and odor-causing bacteria, while taking into consideration the types of textiles. Defining laundering in this manner will help better educate the consumer and highlight areas where more research is needed and how to maximize products and resources. The control of microorganisms during laundering involves mechanical (agitation and soaking), chemical (detergent and bleach), and physical (detergent and temperature) processes. Temperature plays the most important role in terms of pathogen control, requiring temperatures exceeding 40°C to 60°C for proper inactivation, while detergents play a role in reducing the microbial load of laundering through the release of microbes attached to fabrics and the inactivation of microbes sensitive to detergents (e.g., enveloped viruses). The use of additives (enzymes) and bleach (chlorine and activated oxygen) becomes essential in washes with temperatures below 20°C, especially for certain enteric viruses and bacteria. A structured approach is needed that identifies all the steps in the laundering process and attempts to identify each step relative to its importance to infection risk and odor production.
• Anderson-Coughlin, B. L., Craighead, S., Kelly, A., Gartley, S., Vanore, A., Johnson, G., Jiang, C., Haymaker, J., White, C., Foust, D., Duncan, R., East, C., Handy, E. T., Bradshaw, R., Murray, R., Kulkarni, P., Callahan, M. T., Solaiman, S., Betancourt, W., , Gerba, C., et al. (2021). Enteric Viruses and Pepper Mild Mottle Virus Show Significant Correlation in Select Mid-Atlantic Agricultural Waters. Applied and environmental microbiology, 87(13), e0021121.
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  Enteric viruses (EVs) are the largest contributors to foodborne illnesses and outbreaks globally. Their ability to persist in the environment, coupled with the challenges experienced in environmental monitoring, creates a critical aperture through which agricultural crops may become contaminated. This study involved a 17-month investigation of select human EVs and viral indicators in nontraditional irrigation water sources (surface and reclaimed waters) in the Mid-Atlantic region of the United States. Real-time quantitative PCR was used for detection of Aichi virus, hepatitis A virus, and norovirus genotypes I and II (GI and GII, respectively). Pepper mild mottle virus (PMMoV), a common viral indicator of human fecal contamination, was also evaluated, along with atmospheric (air and water temperature, cloud cover, and precipitation 24 h, 7 days, and 14 days prior to sample collection) and physicochemical (dissolved oxygen, pH, salinity, and turbidity) data, to determine whether there were any associations between EVs and measured parameters. EVs were detected more frequently in reclaimed waters (32% [ = 22]) than in surface waters (4% [ = 49]), similar to PMMoV detection frequency in surface (33% [ = 42]) and reclaimed (67% [ = 21]) waters. Our data show a significant correlation between EV and PMMoV ( = 0.628, 0.05) detection levels in reclaimed water samples but not in surface water samples ( = 0.476, 0.78). Water salinity significantly affected the detection of both EVs and PMMoV (0.05), as demonstrated by logistic regression analyses. These results provide relevant insights into the extent and degree of association between human (pathogenic) EVs and water quality data in Mid-Atlantic surface and reclaimed waters, as potential sources for agricultural irrigation. Microbiological analysis of agricultural waters is fundamental to ensure microbial food safety. The highly variable nature of nontraditional sources of irrigation water makes them particularly difficult to test for the presence of viruses. Multiple characteristics influence viral persistence in a water source, as well as affecting the recovery and detection methods that are employed. Testing for a suite of viruses in water samples is often too costly and labor-intensive, making identification of suitable indicators for viral pathogen contamination necessary. The results from this study address two critical data gaps, namely, EV prevalence in surface and reclaimed waters of the Mid-Atlantic region of the United States and subsequent evaluation of physicochemical and atmospheric parameters used to inform the potential for the use of indicators of viral contamination.
• Betancourt, W. Q., Schmitz, B. W., Innes, G. K., Prasek, S. M., Pogreba Brown, K. M., Stark, E. R., Foster, A. R., Sprissler, R. S., Harris, D. T., Sherchan, S. P., Gerba, C. P., & Pepper, I. L. (2021). COVID-19 containment on a college campus via wastewater-based epidemiology, targeted clinical testing and an intervention. The Science of the total environment, 779, 146408.
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  Wastewater-based epidemiology has potential as an early-warning tool for determining the presence of COVID-19 in a community. The University of Arizona (UArizona) utilized WBE paired with clinical testing as a surveillance tool to monitor the UArizona community for SARS-CoV-2 in near real-time, as students re-entered campus in the fall. Positive detection of virus RNA in wastewater lead to selected clinical testing, identification, and isolation of three infected individuals (one symptomatic and two asymptomatic) that averted potential disease transmission. This case study demonstrated the value of WBE as a tool to efficiently utilize resources for COVID-19 prevention and response. Thus, WBE coupled with targeted clinical testing was further conducted on 13 dorms during the course of the Fall semester (Table 3). In total, 91 wastewater samples resulted in positive detection of SARS-CoV-2 RNA that successfully provided an early-warning for at least a single new reported case of infection (positive clinical test) among the residents living in the dorm. Overall, WBE proved to be an accurate diagnostic for new cases of COVID-19 with an 82.0% positive predictive value and an 88.9% negative predictive value. Increases in positive wastewater samples and clinical tests were noted following holiday-related activities. However, shelter-in-place policies proved to be effective in reducing the number of daily reported positive wastewater and clinical tests. This case study provides evidence for WBE paired with clinical testing and public health interventions to effectively contain potential outbreaks of COVID-19 in defined communities.
• Brisolara, K. F., Maal-Bared, R., Sobsey, M. D., Reimers, R. S., Rubin, A., Bastian, R. K., Gerba, C., Smith, J. E., Bibby, K., Kester, G., & Brown, S. (2021). Assessing and managing SARS-CoV-2 occupational health risk to workers handling residuals and biosolids. The Science of the total environment, 774, 145732.
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  Current wastewater worker guidance from the United States Environmental Protection Agency (USEPA) aligns with the Centers for Disease Control and Prevention (CDC) and the Occupational Safety and Health Administration (OSHA) recommendations and states that no additional specific protections against SARS-CoV-2, the virus that causes COVID-19 infections, are recommended for employees involved in wastewater management operations with residuals, sludge, and biosolids at water resource recovery facilities. The USEPA guidance references a document from 2002 that summarizes practices required for protection of workers handling class B biosolids to minimize exposure to pathogens including viruses. While there is no documented evidence that residuals or biosolids of any treatment level contain infectious SARS-CoV-2 or are a source of transmission of this current pandemic strain of coronavirus, this review summarizes and examines whether the provided federal guidance is sufficient to protect workers in view of currently available data on SARS-CoV-2 persistence and transmission. No currently available epidemiological data establishes a direct link between wastewater sludge or biosolids and risk of infection from the SARS-CoV-2. Despite shedding of the RNA of the virus in feces, there is no evidence supporting the presence or transmission of infectious SARS-CoV-2 through the wastewater system or in biosolids. In addition, this review presents previous epidemiologic data related to other non-enveloped viruses. Overall, the risk for exposure to SARS-CoV-2, or any pathogen, decreases with increasing treatment measures. As a result, the highest risk of exposure is related to spreading and handling untreated feces or stool, followed by untreated municipal sludge, the class B biosolids, while lowest risk is associated with spreading or handling Class A biosolids. This review reinforces federal recommendations and the importance of vigilance in applying occupational risk mitigation measures to protect public and occupational health.
• Gerba, C. P. (2021). Differentiating between the possibility and probability of SARS-CoV-2 transmission associated with wastewater: empirical evidence is needed to substantiate risk. FEMS Microbes, doi: 10.1093/femsmc/xtab007.
• Gerba, C. P. (2021). Experimental Study of PhiX174 Resuspension from Mobile Bed Sediment. Journal of irrigation and drainage engineering, 147(5), 04021009.
• Gerba, C. P., & Ben, M. (2021). Inactivation of Coronaviruses and Phage Phi6 from Irradiation across UVC Wavelengths. Environmental Sceince and Technology Letters, 8(5), 425-430.
• Gerba, C. P., & Maal-Bared, R. M. (2021). Implications of SARS-CoV-2 on current and future operation and management of wastewater systems. Water Environment Research, 93, 502-515.
• Gerba, C. P., Ijaz, M. K., McKinney, J., Bright, K. R., & Abney, S. A. (2021). Toilet Hygiene – Review and Research Needs.. Journal of Applied Microbiology, 131(6), 2705-2714. doi:https://doi: 10.1111/jam.15121
• Gerba, C. P., Leija, B. M., Ikner, L. A., Gundy, P., & Rutala, W. A. (2021). Transfer efficiency of an enveloped virus, human coronavirus 229E, from various hard surface fomites to finger pads of the hands. Infection control and hospital epidemiology, 1-3.
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  Respiratory viruses can be transmitted by fomite contact, but no data currently exist on the transfer of enveloped viruses. The transfer efficiency of human coronavirus from various hard surfaces ranged from 0.46% to 49.0%. This information can be used to model the fomite transmission of enveloped viruses.
• Gundy, P., Torrey, J., Gerba, C. P., & Ikner, L. A. (2021). Efficacy of an antimicrobial surface coating against human coronavirus 229E and SARS-CoV-2. American Journal of Infection Control.
• Ikner, L. A., Torrey, J. R., Gundy, P. M., & Gerba, C. P. (2021). Efficacy of an antimicrobial surface coating against human coronavirus 229E and SARS-CoV-2. American journal of infection control, 49(12), 1569-1571.
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  The COVID-19 pandemic has accelerated the demand for alternatives to standard cleaning and disinfection practices. Antiviral coatingsmay provide an alternative to common surface treatments. A newly developed quaternary ammonium polymer coating was applied to stainless steel coupons and evaluated for efficacy against human coronavirus 229E and SARS-CoV-2. The polymer coating reduced levels of both test viruses by greater than 99.9% relative to non-coated stainless steel coupons during a 2-hour contact time.
• Ma, B., Gundy, P. M., Gerba, C. P., Sobsey, M. D., & Linden, K. G. (2021). UV Inactivation of SARS-CoV-2 across the UVC Spectrum: KrCl* Excimer, Mercury-Vapor, and Light-Emitting-Diode (LED) Sources. Applied and environmental microbiology, 87(22), e0153221.
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  Effective disinfection technology to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help reduce viral transmission during the ongoing COVID-19 global pandemic and in the future. UV devices emitting UVC irradiation (200 to 280 nm) have proven to be effective for virus disinfection, but limited information is available for SARS-CoV-2 due to the safety requirements of testing, which is limited to biosafety level 3 (BSL3) laboratories. In this study, inactivation of SARS-CoV-2 in thin-film buffered aqueous solution (pH 7.4) was determined across UVC irradiation wavelengths of 222 to 282 nm from krypton chloride (KrCl*) excimers, a low-pressure mercury-vapor lamp, and two UVC light-emitting diodes. Our results show that all tested UVC devices can effectively inactivate SARS-CoV-2, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate). The inactivation rate constants of SARS-CoV-2 across wavelengths are similar to those for murine hepatitis virus (MHV) from our previous investigation, suggesting that MHV can serve as a reliable surrogate of SARS-CoV-2 with a lower BSL requirement (BSL2) during UV disinfection tests. This study provides fundamental information on UVC's action on SARS-CoV-2 and guidance for achieving reliable disinfection performance with UVC devices. UV light is an effective tool to help stem the spread of respiratory viruses and protect public health in commercial, public, transportation, and health care settings. For effective use of UV, there is a need to determine the efficiency of different UV wavelengths in killing pathogens, specifically SARS-CoV-2, to support efforts to control the ongoing COVID-19 global pandemic and future coronavirus-caused respiratory virus pandemics. We found that SARS-CoV-2 can be inactivated effectively using a broad range of UVC wavelengths, and 222 nm provided the best disinfection performance. Interestingly, 222-nm irradiation has been found to be safe for human exposure up to thresholds that are beyond those effective for inactivating viruses. Therefore, applying UV light from KrCl* excimers in public spaces can effectively help reduce viral aerosol or surface-based transmissions.
• Pepper, I. L., Gerba, C. P., Sherchan, S. P., Harris, D. T., Sprissler, R. S., Foster, A. R., Stark, E. R., Pogreba Brown, K. M., Prasek, S. M., Innes, G. K., Schmitz, B. W., & Betancourt, W. Q. (2021). COVID-19 containment on a college campus via wastewater-based epidemiology, targeted clinical testing and an intervention. Science of the Total Environment.
• Reynolds, K. A., Verhougstraete, M. P., Mena, K. D., Sattar, S. A., Scott, E. A., & Gerba, C. P. (2021). Quantifying pathogen infection risks from household laundry practices. Journal of applied microbiology.
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  Contaminated laundry can spread infections. However, current directives for safe laundering are limited to healthcare settings and not reflective of domestic conditions. We aimed to use quantitative microbial risk assessment to evaluate household laundering practices (e.g., detergent selection, washing and drying temperatures, and sanitizer use) relative to log reductions in pathogens and infection risks during the clothes sorting, washer/dryer loading, folding and storing steps.
• Rosiles-González, G., Carrillo-Jovel, V. H., Alzate-Gaviria, L., Betancourt, W. Q., Gerba, C. P., Moreno-Valenzuela, O. A., Tapia-Tussell, R., & Hernández-Zepeda, C. (2021). Environmental Surveillance of SARS-CoV-2 RNA in Wastewater and Groundwater in Quintana Roo, Mexico. Food and environmental virology, 13(4), 457-469.
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  The presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in wastewater has been reported as a result of fecal shedding of infected individuals. In this study, the occurrence of SARS-CoV-2 RNA was explored in primary-treated wastewater from two municipal wastewater treatment plants in Quintana Roo, Mexico, along with groundwater from sinkholes, a household well, and submarine groundwater discharges. Physicochemical variables were obtained in situ, and coliphage densities were determined. Three virus concentration methods based on adsorption-elution and sequential filtration were used followed by RNA isolation. Quantification of SARS-CoV-2 was done by RT-qPCR using the CDC 2020 assay, 2019-nCoV_N1 and 2019-nCoV_N2. The Pepper mild mottle virus, one of the most abundant RNA viruses in wastewater was quantified by RT-qPCR and compared to SARS-CoV-2 concentrations. The use of three combined virus concentration methods together with two qPCR assays allowed the detection of SARS-CoV-2 RNA in 58% of the wastewater samples analyzed, whereas none of the groundwater samples were positive for SARS-CoV-2 RNA. Concentrations of SARS-CoV-2 in wastewater were from 1.8 × 10 to 7.5 × 10 genome copies per liter (GC l), using the N1 RT-qPCR assay, and from 2.4 × 10 to 5.9 × 10 GC l using the N2 RT-qPCR assay. Based on PMMoV prevalence detected in all wastewater and groundwater samples tested, the three viral concentration methods used could be successfully applied for SARS-CoV-2 RNA detection in further studies. This study represents the first detection of SARS-CoV-2 RNA in wastewater in southeast Mexico and provides a baseline for developing a wastewater-based epidemiology approach in the area.
• Rutala, W. A., Ikner, L. A., Donskey, C. J., Weber, D. J., & Gerba, C. P. (2021). Continuously active disinfectant inactivates severe acute respiratory coronavirus virus 2 (SARS-CoV-2) and human coronavirus 229E two days after the disinfectant was applied and following wear exposures. Infection control and hospital epidemiology, 1-3.
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  The surface environment in rooms of coronavirus disease 2019 (COVID-19) patients may be persistently contaminated despite disinfection. A continuously active disinfectant demonstrated excellent sustained antiviral activity following a 48-hour period of wear and abrasion exposures with reinoculations. Reductions of >4-log were achieved within a 1-minute contact time for severe acute respiratory coronavirus virus 2 (SARS-CoV-2) and the human coronavirus, 229E.
• Schmitz, B. W., Innes, G. K., Prasek, S. M., Betancourt, W. Q., Stark, E. R., Foster, A. R., Abraham, A. G., Gerba, C. P., & Pepper, I. L. (2021). Enumerating asymptomatic COVID-19 cases and estimating SARS-CoV-2 fecal shedding rates via wastewater-based epidemiology. The Science of the total environment, 801, 149794.
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  Wastewater-based epidemiology (WBE) was utilized to monitor SARS-CoV-2 RNA in sewage collected from manholes specific to individual student dormitories (dorms) at the University of Arizona in the fall semester of 2020, which led to successful identification and reduction of SARS-CoV-2 transmission events. Positive wastewater samples triggered clinical testing of residents within that dorm; thus, SARS-CoV-2 infected individuals were identified regardless of symptom expression. This current study examined clinical testing data to determine the abundance of asymptomatic versus symptomatic cases in these defined communities. Nasal and nasopharyngeal swab samples processed via antigen and PCR tests indicated that 79.2% of SARS-CoV-2 infections were asymptomatic, and only 20.8% of positive cases reported COVID-19 symptoms at the time of testing. Clinical data was paired with corresponding wastewater virus concentrations, which enabled calculation of viral shedding rates in feces per infected person. Mean shedding rates averaged from positive wastewater samples across all dorms were 7.30 ± 0.67 log genome copies per gram of feces (gc/g-feces) based on the N1 gene. Quantification of SARS-CoV-2 fecal shedding rates from infected individuals has been the critical missing component necessary for WBE models to measure and predict SARS-CoV-2 infection prevalence in communities. The findings from this study can be utilized to create models that can be used to inform public health prevention and response actions.
• Tousi, E. G., Duan, J. G., Gundy, P. M., Bright, K. R., & Gerba, C. P. (2021). Evaluation of E. coli in sediment for assessing irrigation water quality using machine learning. The Science of the total environment, 799, 149286.
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  Fresh produce irrigated with contaminated water poses a substantial risk to human health. This study evaluated the impact of incorporating sediment information on improving the performance of machine learning models to quantify E. coli level in irrigation water. Field samples were collected from irrigation canals in the Southwest U.S., for which meteorological, chemical, and physical water quality variables as well as three additional flow and sediment properties: the concentration of E. coli in sediment, sediment median size, and bed shear stress. Water quality was classified based on E. coli concentration exceeding two standard levels: 1 E. coli and 126 E. coli colony forming units (CFU) per 100 ml of irrigation water. Two series of features, including (FIS) and excluding (FES) sediment features, were selected using multi-variant filter feature selection. The correlation analysis revealed the inclusion of sediment features improves the correlation with the target standards for E. coli compared to the models excluding these features. Support vector machine, logistic regression, and ridge classifier were tested in this study. The support vector machine model performed the best for both targeted standards. Besides, incorporating sediment features improved all models' performance. Therefore, the concentration of E. coli in sediment and bed shear stress are major factors influencing E. coli concentration in irrigation water.
• Weber, D., Donskey, C., Rutala, W., Gerba, C. P., & Ikner, L. A. (2021). Continuously active disinfectant inactivates SARS-CoV-2 and human coronavirus 229E two days after the disinfectant was applied and following wear exposures. Infection Control & Hospital Epidemiology.
• Wilson, A. M., Verhougstraete, M. P., Beamer, P. I., King, M. F., Reynolds, K. A., & Gerba, C. P. (2021). Frequency of hand-to-head, -mouth, -eyes, and -nose contacts for adults and children during eating and non-eating macro-activities. Journal of exposure science & environmental epidemiology, 31(1), 34-44.
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  Hand-to-face contacts are important for estimating chemical and microbial exposures. Few studies describe children's hand-to-eye or -nose contacts or adults' hand-to-face contacts. The study objective was to characterize hand-to-head (mouth, eyes, nose, and other) contacts for children in a daycare and adults in multiple locations. Macro-activities and sequences of hand-to-face contacts were recorded for 263 people observed for 30 min each. Statistically significant differences between locations, males and females, adults and children, and during eating and non-eating macro-activities were evaluated. Discrete Markov chains were fit to observed contact sequences and compared among adults and children during eating and non-eating macro-activities. No significant differences in contact frequency were observed between males and females with the exception of hand-to-nose contacts. Children tended to touch the mouth, eyes, and nose more frequently than adults during non-eating macro-activities. Significant differences in contact frequency were observed between locations. Transitional probabilities indicated that children make repetitive mouth, eye, and nose contacts while adults frequently transition to contacts of the head other than the mouth, eyes, or nose. More data are needed to evaluate the effect of age on adults' contact frequencies and to confirm lack of statistically significant differences between adults and children during eating macro-activities.
• Betancourt, W. Q., Schijven, J., Regnery, J., Wing, A., Morrison, C. M., Drewes, J. E., & Gerba, C. P. (2019). Variable non-linear removal of viruses during transport through a saturated soil column. Journal of contaminant hydrology, 223, 103479.
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  Reduction of viral surrogates (bacteriophage MS2 and murine norovirus-1 [MNV-1]) and viruses naturally present in wastewater (enteroviruses, adenoviruses, Aichi viruses, reovirus, pepper mild mottle virus) was studied in a long-term experiment simulating soil-aquifer treatment of a non-disinfected secondary treated wastewater effluent blend using a 4.4 m deep saturated soil column (95% sand, 4% silt, 1% clay) with a hydraulic residence time of 15.4 days under predominantly anoxic redox conditions. Water samples were collected over a four-week period from the column inflow and outflow as well as from seven intermediate sampling ports at different depths. Removal of MS2 was 3.5 log over 4.4 m and removal of MNV-1 was 3 log over 0.3 m. Notably, MNV-1 was removed to below detection limit within 0.3 m of soil passage. In secondary treated wastewater effluent, MNV-1 RNA and MS2 RNA degraded at a first-order rate of 0.59 day and 0.12 day, respectively. In 15.4 days, the time to pass the soil column, the RNA-degradation of MS2 would amount to 0.8 log and in one day that of MNV-1 0.3 log implying that attachment of MNV-1 and MS2 to the sandy soil took place. Among the indigenous viruses, genome copies reductions were observed for Aichi virus (4.9 log) and for pepper mild mottle virus (4.4 log). This study demonstrated that under saturated flow and predominantly anoxic redox conditions MS2 removal was non-linear and could be described well by a power-law relation. Pepper mild mottle virus was removed less than all of the other viruses studied, which substantiates field studies at managed aquifer recharge sites, suggesting it may be a conservative model/tracer for enteric virus transport through soil.
• Bivins, A., North, D., Ahmad, A., Ahmed, W., Alm, E., Been, F., Bhattacharya, P., Bijlsma, L., Boehm, A. B., Brown, J., Buttiglieri, G., Calabro, V., Carducci, A., Castiglioni, S., Cetecioglu Gurol, Z., Chakraborty, S., Costa, F., Curcio, S., de Los Reyes, F. L., , Delgado Vela, J., et al. (2020). Wastewater-Based Epidemiology: Global Collaborative to Maximize Contributions in the Fight Against COVID-19. Environmental science & technology, 54(13), 7754-7757.
• Dev Kumar, G., Mishra, A., Dunn, L., Townsend, A., Oguadinma, I. C., Bright, K. R., & Gerba, C. P. (2020). Biocides and Novel Antimicrobial Agents for the Mitigation of Coronaviruses. Frontiers in microbiology, 11, 1351.
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  In December, 2019, a highly infectious and rapidly spreading new pneumonia of unknown cause was reported to the Chinese WHO Country Office. A cluster of these cases had appeared in Wuhan, a city in the Hubei Province of China. These infections were found to be caused by a new coronavirus which was given the name "2019 novel coronavirus" (2019-nCoV). It was later renamed "severe acute respiratory syndrome coronavirus 2," or SARS-CoV-2 by the International Committee on Taxonomy of Viruses on February 11, 2020. It was named SARS-CoV-2 due to its close genetic similarity to the coronavirus which caused the SARS outbreak in 2002 (SARS-CoV-1). The aim of this review is to provide information, primarily to the food industry, regarding a range of biocides effective in eliminating or reducing the presence of coronaviruses from fomites, skin, oral/nasal mucosa, air, and food contact surfaces. As several EPA approved sanitizers against SARS-CoV-2 are commonly used by food processors, these compounds are primarily discussed as much of the industry already has them on site and is familiar with their application and use. Specifically, we focused on the effects of alcohols, povidone iodine, quaternary ammonium compounds, hydrogen peroxide, sodium hypochlorite (NaOCl), peroxyacetic acid (PAA), chlorine dioxide, ozone, ultraviolet light, metals, and plant-based antimicrobials. This review highlights the differences in the resistance or susceptibility of different strains of coronaviruses, or similar viruses, to these antimicrobial agents.
• Ellingson, K. D., Pogreba-Brown, K., Gerba, C. P., & Elliott, S. P. (2020). Impact of a Novel Antimicrobial Surface Coating on Health Care-Associated Infections and Environmental Bioburden at 2 Urban Hospitals. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 71(8), 1807-1813.
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  Approximately 1 in 25 people admitted to a hospital in the United States will suffer a health care-associated infection (HAI). Environmental contamination of hospital surfaces contributes to HAI transmission. We investigated the impact of an antimicrobial surface coating on HAIs and environmental bioburdens at 2 urban hospitals.
• Gerba, C. P., & Betancourt, W. Q. (2019). Assessing the Occurrence of Waterborne Viruses in Reuse Systems: Analytical Limits and Needs. Pathogens (Basel, Switzerland), 8(3).
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  Detection of waterborne enteric viruses is an essential tool in assessing the risk of waterborne transmission. Cell culture is considered a gold standard for detection of these viruses. However, it is important to recognize the uncertainty and limitations of enteric virus detection in cell culture. Cell culture cannot support replication of all virus types and strains, and numerous factors control the efficacy of specific virus detection assays, including chemical additives, cell culture passage number, and sequential passage of a sample in cell culture. These factors can result in a 2- to 100-fold underestimation of virus infectivity. Molecular methods reduce the time for detection of viruses and are useful for detection of those that do not produce cytopathogenic effects. The usefulness of polymerase chain reaction (PCR) to access virus infectivity has been demonstrated for only a limited number of enteric viruses and is limited by an understanding of the mechanism of virus inactivation. All of these issues are important to consider when assessing waterborne infectious viruses and expected goals on virus reductions needed for recycled water. The use of safety factors to account for this may be useful to ensure that the risks in drinking water and recycled water for potable reuse are minimized.
• Gerba, C. P., Bright, K. R., Oguadinma, I. C., Townsend, A., Dunn, L., Mishra, A., & Kumar, G. D. (2020). Biocides and novel antimicrobial agents for the mitigation of coronaviruses.. Frontiers in Microbiology, 11, 1351. doi:https://doi.org/10.3389/fmicb.2020.01351
• Gerba, C. P., Pepper, I. L., Lopez, G. U., Quintanar, D. R., Betancourt, W. Q., & Morrison, C. M. (2020). Potential Indicators of Virus Transport and Removal during Soil Aquifer Treatment of Treated Wastewater Effluent. International Water Association.
• Ijaz, M. K., Sattar, S. A., Rubino, J. R., Nims, R. W., & Gerba, C. P. (2020). Combating SARS-CoV-2: leveraging microbicidal experiences with other emerging/re-emerging viruses. PeerJ, 8, e9914.
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  The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Wuhan City, China, late in December 2019 is an example of an emerging zoonotic virus that threatens public health and international travel and commerce. When such a virus emerges, there is often insufficient specific information available on mechanisms of virus dissemination from animal-to-human or from person-to-person, on the level or route of infection transmissibility or of viral release in body secretions/excretions, and on the survival of virus in aerosols or on surfaces. The effectiveness of available virucidal agents and hygiene practices as interventions for disrupting the spread of infection and the associated diseases may not be clear for the emerging virus. In the present review, we suggest that approaches for infection prevention and control (IPAC) for SARS-CoV-2 and future emerging/re-emerging viruses can be invoked based on pre-existing data on microbicidal and hygiene effectiveness for related and unrelated enveloped viruses.
• Kitajima, M., Ahmed, W., Bibby, K., Carducci, A., Gerba, C. P., Hamilton, K. A., Haramoto, E., & Rose, J. B. (2020). SARS-CoV-2 in wastewater: State of the knowledge and research needs. The Science of the total environment, 739, 139076.
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  The ongoing global pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been a Public Health Emergency of International Concern, which was officially declared by the World Health Organization. SARS-CoV-2 is a member of the family Coronaviridae that consists of a group of enveloped viruses with single-stranded RNA genome, which cause diseases ranging from common colds to acute respiratory distress syndrome. Although the major transmission routes of SARS-CoV-2 are inhalation of aerosol/droplet and person-to-person contact, currently available evidence indicates that the viral RNA is present in wastewater, suggesting the need to better understand wastewater as potential sources of epidemiological data and human health risks. Here, we review the current knowledge related to the potential of wastewater surveillance to understand the epidemiology of COVID-19, methodologies for the detection and quantification of SARS-CoV-2 in wastewater, and information relevant for human health risk assessment of SARS-CoV-2. There has been growing evidence of gastrointestinal symptoms caused by SARS-CoV-2 infections and the presence of viral RNA not only in feces of infected individuals but also in wastewater. One of the major challenges in SARS-CoV-2 detection/quantification in wastewater samples is the lack of an optimized and standardized protocol. Currently available data are also limited for conducting a quantitative microbial risk assessment (QMRA) for SARS-CoV-2 exposure pathways. However, modeling-based approaches have a potential role to play in reducing the impact of the ongoing COVID-19 outbreak. Furthermore, QMRA parameters obtained from previous studies on relevant respiratory viruses help to inform risk assessments of SARS-CoV-2. Our understanding on the potential role of wastewater in SARS-CoV-2 transmission is largely limited by knowledge gaps in its occurrence, persistence, and removal in wastewater. There is an urgent need for further research to establish methodologies for wastewater surveillance and understand the implications of the presence of SARS-CoV-2 in wastewater.
• Maal-Bared, R., Brisolara, K., Munakata, N., Bibby, K., Gerba, C., Sobsey, M., Schaefer, S., Swift, J., Gary, L., Sherchan, S., Babatola, A., Bastian, R., Olabode, L., Reimers, R., & Rubin, A. (2020). Implications of SARS-CoV-2 on current and future operation and management of wastewater systems. Water environment research : a research publication of the Water Environment Federation.
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  While researchers have acknowledged the potential role of environmental scientists, engineers, and industrial hygienists during this pandemic, the role of the water utility professional is often overlooked. The wastewater sector is critical to public health protection and employs collection and treatment system workers who perform tasks with high potential for exposures to biological agents. While various technical guidances and reports have initially provided direction to the water sector, the rapidly growing body of research publications necessitates the constant review of these papers and data synthesis. This paper presents the latest findings and highlights their implications from a water and wastewater utility operation and management perspective. PRACTITIONER POINTS: Extrapolation from SARS-CoV-1 and MERS-CoV, as well as other surrogates, has helped predicting SARS-CoV-2 behavior and risk management. Data from treated wastewater effluent suggest that current processes are sufficient for SARS-CoV-2 control. Scientific evidence supports the possibility of fecal-oral transmission for SARS-CoV-2. Limited evidence supports the potential survival of infective SARS-CoV-2 on surfaces and in aerosols and the efficacy of control measures at reducing transmission. Protective practices and PPE can protect workers from SARS-CoV-2 and other pathogens found in wastewater.
• Maal-Bared, R., Sobsey, M., Bibby, K., Sherchan, S. P., Fitzmorris, K. B., Munakata, N., Gerba, C., Schaefer, S., Swift, J., Gary, L., Babatola, A., Bastian, R., Olabode, L., Reimers, R., Rubin, A., Kester, G., & Casson, L. (2020). Letter to the Editor regarding Mathavarajah et al. (2020) Pandemic danger to the deep: The risk of marine mammals contracting SARS-CoV-2 from wastewater. The Science of the total environment, 144855.
• Maillard, J. Y., Bloomfield, S. F., Courvalin, P., Essack, S. Y., Gandra, S., Gerba, C. P., Rubino, J. R., & Scott, E. A. (2020). Reducing antibiotic prescribing and addressing the global problem of antibiotic resistance by targeted hygiene in the home and everyday life settings: A position paper. American journal of infection control, 48(9), 1090-1099.
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  Antimicrobial resistance (AMR) continues to threaten global health. Although global and national AMR action plans are in place, infection prevention and control is primarily discussed in the context of health care facilities with home and everyday life settings barely addressed. As seen with the recent global SARS-CoV-2 pandemic, everyday hygiene measures can play an important role in containing the threat from infectious microorganisms. This position paper has been developed following a meeting of global experts in London, 2019. It presents evidence that home and community settings are important for infection transmission and also the acquisition and spread of AMR. It also demonstrates that the targeted hygiene approach offers a framework for maximizing protection against colonization and infections, thereby reducing antibiotic prescribing and minimizing selection pressure for the development of antibiotic resistance. If combined with the provision of clean water and sanitation, targeted hygiene can reduce the circulation of resistant bacteria in homes and communities, regardless of a country's Human Development Index (overall social and economic development). Achieving a reduction of AMR strains in health care settings requires a mirrored reduction in the community. The authors call upon national and international policy makers, health agencies, and health care professionals to further recognize the importance of targeted hygiene in the home and everyday life settings for preventing and controlling infection, in a unified quest to tackle AMR.
• Morrison, C. M., Betancourt, W. Q., Quintanar, D. R., Lopez, G. U., Pepper, I. L., & Gerba, C. P. (2020). Potential indicators of virus transport and removal during soil aquifer treatment of treated wastewater effluent. Water research, 177, 115812.
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  Increased water demands have led to a notable interest in the use of treated wastewater for reuse. Typically, this results from the implementation of advanced treatment of final effluent from wastewater treatment plants prior to reuse for potable or non-potable purposes. Soil aquifer treatment (SAT) is a natural treatment process in which water from sources of varying quality is infiltrated into the soil to further improve its quality. The goal of this study was to determine the log reduction values (LRVs) of viruses naturally present in treated effluent and evaluate two potential indicators of virus removal and transport, pepper mild mottle virus (PMMoV) and crAssphage, during SAT of treated effluent. Groundwater was sampled at three wells with different attributes within the Sweetwater Recharge Facility (SWRF) in Tucson, AZ. These sites vary greatly in operational parameters such as effluent infiltration rates and wetting/drying cycles, which may influence virus removal efficiency. Detection of adenovirus, enterovirus, PMMoV, and crAssphage were determined by qPCR/RT-qPCR and log reduction values (LRVs) were determined. PMMoV and crAssphage were detected in groundwater associated with a set of recharge basins that exhibited shorter wetting/drying cycles and faster infiltration rates. LRVs for crAssphage and PMMoV at this site ranged from 3.9 to 5.8, respectively. Moreover, PMMoV was detected downflow of the SAT sites, indicating the potential degradation of microbial groundwater quality in the region surrounding managed aquifer recharge facilities. Overall, PMMoV and crAssphage showed potential as conservative process indicators of virus removal during SAT, particularly for attribution of LRV credits. Moreover, the detection of these viruses indicated the potential influence of wetting/drying cycles on virus removal by SAT, a parameter that has not yet been studied with respect to biological contaminants.
• Panthi, S., Sapkota, A. R., Raspanti, G., Allard, S. M., Bui, A., Craddock, H. A., Murray, R., Zhu, L., East, C., Handy, E., Callahan, M. T., Haymaker, J., Kulkarni, P., Anderson, B., Craighead, S., Gartley, S., Vanore, A., Betancourt, W. Q., Duncan, R., , Foust, D., et al. (2019). Pharmaceuticals, herbicides, and disinfectants in agricultural water sources. Environmental research, 174, 1-8.
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  Agricultural water withdrawals account for the largest proportion of global freshwater use. Increasing municipal water demands and droughts are straining agricultural water supplies. Therefore, alternative solutions to agricultural water crises are urgently needed, including the use of nontraditional water sources such as advanced treated wastewater or reclaimed water, brackish water, return flows, and effluent from produce processing facilities. However, it is critical to ensure that such usage does not compromise soil, crop, and public health. Here, we characterized five different nontraditional water types (n = 357 samples) for the presence of pharmaceuticals, herbicides, and disinfectants using ultra-high-pressure liquid chromatography tandem mass spectrometry based method (UPLC-MS/MS). We then evaluated whether the levels of these contaminants were influenced by season. The highest level of herbicides (atrazine) was detected in untreated pond water (median concentration 135.9 ng/L). Reclaimed water had the highest levels of antibiotics and stimulants including azithromycin (215 ng/L), sulfamethoxazole (232.1 ng/L), and caffeine (89.4 ng/L). Produce processing plant water also tended to have high levels of atrazine (102.7 ng/L) and ciprofloxacin (80.1 ng/L). In addition, we observed seasonal variability across water types, with the highest atrazine concentrations observed during summer months, while the highest median azithromycin concentrations were observed in reclaimed water during the winter season. Further studies are needed to evaluate if economically feasible on-farm water treatment technologies can effectively remove such contaminants from nontraditional irrigation water sources.
• Sassi, H. P., van Ogtrop, F., Morrison, C. M., Zhou, K., Duan, J. G., & Gerba, C. P. (2020). Sediment re-suspension as a potential mechanism for viral and bacterial contaminants. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 55(12), 1398-1405.
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  Pathogenic enteric viruses and bacteria tend to occur in higher concentrations and survive longer in aquatic sediments than suspended in the water column. Re-suspension of these organisms can result in a significant degradation of overlying water quality. Additionally, the re-suspension of microbial pathogens in artificial irrigation canals could endanger the consumption of fresh and ready-to-eat produce. Irrigation water has been implicated in numerous fresh produce outbreaks over the last 30 years. This study aimed to quantify the proportions of bacterial and viral re-suspension from sediment in a recirculating flume with varying velocities. MS2 coliphage and were found to re-suspend at rates that were not significantly different, despite organism size differences. However, re-suspension rates from sand and clay were significantly different. This suggests that likely sediment-associated particles were recovered with the organisms attached. Similar re-suspension rates are hypothesized to be due to the dynamics of sediment transport, rather than that of the organisms themselves. This study also indicated that the re-suspension of sediment at very low velocities (e.g., less than 10 cm/s), could impact the microbiological quality of the overlaying water. Results from this study conclude that sediment could be a viable mechanism for irrigation water contamination.
• Schmitz, B. W., Innes, G. K., Xue, J., Gerba, C. P., Pepper, I. L., & Sherchan, S. (2020). Reduction of erythromycin resistance gene erm(F) and class 1 integron-integrase genes in wastewater by Bardenpho treatment. Water environment research : a research publication of the Water Environment Federation, 92(7), 1042-1050.
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  Wastewaters routinely contain antibiotic-resistant bacteria (ARB) and genes (ARG) that are removed to a varying degree during wastewater treatment. This study investigated the removal of the erythromycin ribosome methylase class F (erm(F)) and class 1 integron-integrase (intI1) genes at each stage from two water resource recovery facilities in southern Arizona. Although genes were significantly reduced by Bardenpho treatment, erm(F) and intI1 were still observed in ≥ 9 and 7 out of 12 secondary effluent samples. Primary processes via sedimentation or dissolved air flotation, as well as chlorine disinfection, did not significantly impact erm(F) and intI1 concentrations. Therefore, Bardenpho treatment was critical to reduce erm(F) and intI1. Concentrations of erm(F) and intI1 were compared with each other and other markers for anthropogenic pollution. Results from this study support intI1 as one suitable marker to measure erythromycin resistance genes in wastewater, as intI1 was found at higher concentrations, persisted more throughout treatment, and correlated with erm(F) at nearly every treatment stage. PRACTITIONER POINTS: Bardenpho treatment was the key process responsible for the reduction of intI1 and erm(F) genes during wastewater treatment. Primary treatment and chlorine disinfection did not impact erm(F) and intI1 gene concentrations. The intI1 gene is a suitable marker for measuring erm(F) genes in wastewater.
• Verhougstraete, M., Reynolds, K. A., Pearce-Walker, J., & Gerba, C. (2020). Cost-benefit analysis of point-of-use devices for health risks reduction from pathogens in drinking water. Journal of water and health, 18(6), 968-982.
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  Microbial contamination of drinking water post-municipal treatment is difficult to predict as a risk factor for human health. One method to reduce morbidity or mortality from unpredictable exposures is through point-of-use (POU) treatment devices. The goal of this project was to assess the cost-benefit of POU water treatment at the tap in terms of protection from microbes in drinking water. This project estimated: (1) incidence of acute illness (AI), sequela, and mortality associated with waterborne pathogens; (2) illness reduction rates from using POU devices; and (3) healthcare cost reductions associated with POU devices. Infection rates and costs associated with 10 of the most common waterborne pathogens were identified and used to calculate national annual costs. We estimated 9M AI, 0.6M sequela, and 1,400 mortality cases that occur annually in the USA from these pathogens. The greatest cost-benefit was seen when considering the totality of disease burden reduction (AI, sequela, and mortality) including all pathogens at a national level and applying a 35% infection reduction, resulting in a total cost per averted disease case of $1,815. This study suggests that it is cost-beneficial to prevent water-related illness using POU devices.
• Wilson, A. M., Reynolds, K. A., Jaykus, L. A., Escudero-Abarca, B., & Gerba, C. P. (2020). Comparison of estimated norovirus infection risk reductions for a single fomite contact scenario with residual and nonresidual hand sanitizers. American journal of infection control, 48(5), 538-544.
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  The purpose of this study was to relate experimentally measured log human norovirus reductions for a nonresidual (60% ethanol) and a residual (quaternary ammonium-based) hand sanitizer to infection risk reductions.
• Abd-Elmaksoud, S., Castro-Del Campo, N., Gerba, C. P., Pepper, I. L., & Bright, K. R. (2019). Comparative Assessment of BGM and PLC/PRF/5 Cell Lines for Enteric Virus Detection in Biosolids. FOOD AND ENVIRONMENTAL VIROLOGY, 11(1), 32-39. doi:https://doi.org/10.1007/s12560-019-09366-4
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  The buffalo green monkey (BGM) cell line is required for the detection of enteric viruses in biosolids through a total culturable viral assay (TCVA) by the United States Environmental Protection Agency. In the present study, BGM and PLC/PRF/5 cell lines were evaluated for TCVA and for their use in determining the incidence of adenoviruses and enteroviruses in raw sludge and Class B biosolids. Six raw sludge and 17 Class B biosolid samples were collected from 13 wastewater treatment plants from seven U.S. states. Samples were processed via organic flocculation and concentrate volumes equivalent to 4 g total solids were assayed on BGM and PLC/PRF/5 cells. Cell monolayers were observed for cytopathic effect (CPE) after two 14-days passages. Cell lysates were tested for the presence of adenoviruses and enteroviruses by PCR or RT-PCR. The PLC/PRF/5 cells detected more culturable viruses than the BGM cells by CPE (73.9% vs. 56.5%, respectively). 52% of the samples were positive for CPE using both cell lines. No viruses were detected in either cell line by PCR in flasks in which CPE was not observed. No adenoviruses were detected in 13 CPE-positive samples from BGM lysates. In contrast, of the 17 samples exhibiting CPE on PLC/PRF/5 cells, 14 were positive for adenoviruses (82.4%). In conclusion, PLC/PRF/5 cells were superior for the detection of adenoviruses in both raw sludge and Class B biosolids. Thus, the use of BGM cells alone for TCVA may underestimate the viral concentration in sludge/biosolid samples.
• Abd-Elmaksoud, S., Castro-Del Campo, N., Gerba, C. P., Pepper, I. L., & Bright, K. R. (2019). Comparative Assessment of BGM and PLC/PRF/5 Cell Lines for Enteric Virus Detection in Biosolids. Food and environmental virology.
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  The buffalo green monkey (BGM) cell line is required for the detection of enteric viruses in biosolids through a total culturable viral assay (TCVA) by the United States Environmental Protection Agency. In the present study, BGM and PLC/PRF/5 cell lines were evaluated for TCVA and for their use in determining the incidence of adenoviruses and enteroviruses in raw sludge and Class B biosolids. Six raw sludge and 17 Class B biosolid samples were collected from 13 wastewater treatment plants from seven U.S. states. Samples were processed via organic flocculation and concentrate volumes equivalent to 4 g total solids were assayed on BGM and PLC/PRF/5 cells. Cell monolayers were observed for cytopathic effect (CPE) after two 14-days passages. Cell lysates were tested for the presence of adenoviruses and enteroviruses by PCR or RT-PCR. The PLC/PRF/5 cells detected more culturable viruses than the BGM cells by CPE (73.9% vs. 56.5%, respectively). 52% of the samples were positive for CPE using both cell lines. No viruses were detected in either cell line by PCR in flasks in which CPE was not observed. No adenoviruses were detected in 13 CPE-positive samples from BGM lysates. In contrast, of the 17 samples exhibiting CPE on PLC/PRF/5 cells, 14 were positive for adenoviruses (82.4%). In conclusion, PLC/PRF/5 cells were superior for the detection of adenoviruses in both raw sludge and Class B biosolids. Thus, the use of BGM cells alone for TCVA may underestimate the viral concentration in sludge/biosolid samples.
• Canales, R. A., Reynolds, K. A., Wilson, A. M., Fankem, S. L., Weir, M. H., Rose, J. B., Abd-Elmaksoud, S., & Gerba, C. P. (2019). Modeling the role of fomites in a norovirus outbreak. Journal of occupational and environmental hygiene, 1-11.
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  Norovirus accounts for a large portion of the gastroenteritis disease burden, and outbreaks have occurred in a wide variety of environments. Understanding the role of fomites in norovirus transmission will inform behavioral interventions, such as hand washing and surface disinfection. The purpose of this study was to estimate the contribution of fomite-mediated exposures to infection and illness risks in outbreaks. A simulation model in discrete time that accounted for hand-to-porous surfaces, hand-to-nonporous surfaces, hand-to-mouth, -eyes, -nose, and hand washing events was used to predict 17 hr of simulated human behavior. Norovirus concentrations originated from monitoring contamination levels on surfaces during an outbreak on houseboats. To predict infection risk, two dose-response models (fractional Poisson and F hypergeometric) were used to capture a range of infection risks. A triangular distribution describing the conditional probability of illness given an infection was multiplied by modeled infection risks to estimate illness risks. Infection risks ranged from 70.22% to 72.20% and illness risks ranged from 21.29% to 70.36%. A sensitivity analysis revealed that the number of hand-to-mouth contacts and the number of hand washing events had strong relationships with model-predicted doses. Predicted illness risks overlapped with leisure setting and environmental attack rates reported in the literature. In the outbreak associated with the viral concentrations used in this study, attack rates ranged from 50% to 86%. This model suggests that fomites may have accounted for 25% to 82% of illnesses in this outbreak. Fomite-mediated exposures may contribute to a large portion of total attack rates in outbreaks involving multiple transmission modes. The findings of this study reinforce the importance of frequent fomite cleaning and hand washing, especially when ill persons are present.
• Elliott, S. P., Gerba, C. P., Pogreba Brown, K. M., & Ellingson, K. (2019). Impact of a Novel Antimicrobial Surface Coating on Healthcare-Associated Infections and Environmental Bioburden at Two Urban Hospitals. Clinical Infectious Diseases. doi:https://doi.org/10.1093/cid/ciz1077
• Gerba, C. P. (2019). Reduction of Arcobacter at two conventional wastewater treatment plants in Spouthern Arizona, USA. Pathogens, 8, 175. doi:10.3390/pathogens8040175
• Gerba, C. P. (2019). Varible non-linear removal of viruses during transport through a saturated soil column. Journal of Contaminate Hydrology, 223. doi:https://doi.org/10.1016/j.jconhyd.2019.04.002
• Ghaju Shrestha, R., Sherchan, S. P., Kitajima, M., Tanaka, Y., Gerba, C. P., & Haramoto, E. (2019). Reduction of at Two Conventional Wastewater Treatment Plants in Southern Arizona, USA. Pathogens (Basel, Switzerland), 8(4).
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  This study aimed to identify the bacterial community in two wastewater treatment plants (WWTPs) and to determine the occurrence and reduction of , along with virulence genes ( and ). A total of 48 samples (24 influent and 24 effluent) were collected at two WWTPs in southern Arizona in the United States, monthly from August 2011 to July 2012. Bacterial DNA extract was utilized for 16S rRNA metagenomic sequencing. Quantification of 16S rRNA gene was conducted using a recently developed SYBR Green-based quantitative PCR assay Among 847 genera identified, 113 (13%) were identified as potentially pathogenic bacteria. 16S rRNA gene was detected in all influent samples and ten (83%) and nine (75%) effluent samples at each plant, respectively. Log reduction ratios of 16S rRNA gene in Plant A and Plant B were 1.7 ± 0.9 ( = 10) and 2.3 ± 1.5 ( = 9), respectively. The gene was detected by quantitative PCR in eleven (92%) and twelve (100%) of 12 influent samples from Plant A and Plant B, respectively, while the gene was detected in eight (67%) and six (50%) influent samples from Plant A and Plant B, respectively. The prevalence of potentially pathogenic bacteria in WWTP effluent indicated the need for disinfection before discharge into the environment.
• Kurgat, E. K., Sexton, J. D., Garavito, F., Reynolds, A., Contreras, R. D., Gerba, C. P., Leslie, R. A., Edmonds-Wilson, S. L., & Reynolds, K. A. (2019). Impact of a hygiene intervention on virus spread in an office building. International journal of hygiene and environmental health.
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  Viral illnesses have a significant direct and indirect impact on the workplace that burdens employers with increased healthcare costs, low productivity, and absenteeism. Workers' direct contact with each other and contaminated surfaces contributes to the spread of viruses at work. This study quantifies the impact of an office wellness intervention (OWI) to reduce viral load in the workplace. The OWI includes the use of a spray disinfectant on high-touch surfaces and providing workers with alcohol-based hand sanitizer gel and hand sanitizing wipes along with user instructions. Viral transmission was monitored by applying an MS2 phage tracer to a door handle and the hand of a single volunteer participant. At the same time, a placebo inoculum was applied to the hands of four additional volunteers. The purpose was to evaluate the concentration of viruses on workers' hands and office surfaces before and after the OWI. Results showed that the OWI significantly reduced viable phage concentrations per surface area on participants' hands, shared fomites, and personal fomites (p = 0.0001) with an 85.4% average reduction. Reduction of virus concentrations on hands and fomites is expected to subsequently minimize the risk of infections from common enteric and respiratory pathogens. The surfaces identified as most contaminated were the refrigerator, drawer handles and sink faucets in the break room, along with pushbar on the main exit of the building, and the soap dispensers in the women's restroom. A comparison of contamination in different locations within the office showed that the break room and women's restrooms were the sites with the highest tracer counts. Results of this study can be used to inform quantitative microbial risk assessment (QMRA) models aimed at defining the relationship between surface contamination, pathogen exposure and the probability of disease that contributes to high healthcare costs, absenteeism, presenteeism, and loss of productivity in the workplace.
• Lamori, J. G., Xue, J., Rachmadi, A. T., Lopez, G. U., Kitajima, M., Gerba, C. P., Pepper, I. L., Brooks, J. P., & Sherchan, S. (2019). Removal of fecal indicator bacteria and antibiotic resistant genes in constructed wetlands. Environmental science and pollution research international, 26(10), 10188-10197.
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  Wastewater discharge evidently increased bacterial diversity in the receiving waterbodies. The objective of this study was to evaluate the effectiveness of a constructed wetland in reducing fecal indicator bacteria (FIB) and antibiotic resistant genes (ARGs). We determined the prevalence and attenuation of fecal indicator bacteria including Escherichia coli and enterococci, along with ARGs, and human-associated Bacteroidales (HF183) markers by quantitative polymerase chain reaction (qPCR) method. Three types of water samples (inlet, intermediate, and outlet) from a constructed wetland were collected once a month from May to December in 2013. The overall reduction of E. coli was 50.0% based on culture method. According to the qPCR result, the overall removal rate of E. coli was only 6.7%. Enterococci were found in 62.5% of the wetland samples. HF183 genetic marker was detected in all final effluent samples with concentration ranging from 1.8 to 4.22 log gene copies (GC)/100 ml. Of the ARGs tested, erythromycin resistance genes (ermF) were detected in 79.2% of the wetland samples. The class 1 integrase (intI1) was detected in all water samples with concentration ranging from 0.83 to 5.54 log GC/100 ml. The overall removal rates of enterococci, HF183, intI1, and ermF were 84.0%, 66.6%, 67.2%, and 13.1%, respectively.
• Mitchell, J. B., Sifuentes, L. Y., Wissler, A., Abd-Elmaksoud, S., Lopez, G. U., & Gerba, C. P. (2019). Modelling of ultraviolet light inactivation kinetics of methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, Clostridium difficile spores and murine norovirus on fomite surfaces. Journal of applied microbiology, 126(1), 58-67.
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  Quantitative data on the doses needed to inactivate micro-organisms on fomites are not available for ultraviolet applications. The goal of this study was to determine the doses of UV light needed to reduce bacteria and murine norovirus (MNV) on hard surface fomites through experimentation and to identify appropriate models for predicting targeted levels of reduction.
• Reynolds, K. A., Sexton, J. D., Pivo, T., Humphrey, K., Leslie, R. A., & Gerba, C. P. (2019). Microbial transmission in an outpatient clinic and impact of an intervention with an ethanol-based disinfectant. American journal of infection control, 47(2), 128-132.
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  Halting the spread of harmful microbes requires an understanding of their transmission via hands and fomites. Previous studies explored acute and long-term care environments but not outpatient clinics. Objectives of this study were to track microbial movement throughout an outpatient clinic and evaluate the impact of a disinfectant spray intervention targeting high-touch point surfaces.
• Sherchan, S., Pepper, I. L., Gerba, C. P., Kitajima, M., Lopez, G. U., Taruna, A., Xue, J., & Lamori, J. G. (2018). Removal of fecal indicator bacteria and antibiotic resistant genes in constructed wetlands. Journal of Environmental Management.
• Sherchan, S., Pepper, I. L., Gerba, C. P., Kitajima, M., Lopez, G. U., Taruna, A., Xue, J., & Lamori, J. G. (2019). Removal of fecal indicator bacteria and antibiotic resistant genes in constructed wetlands. Environmental Science and Pollution Research.
• Sicairos-Ruelas, E. E., Gerba, C. P., & Bright, K. R. (2019). Efficacy of copper and silver as residual disinfectants in drinking water. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 1-10.
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  Contamination events and biofilms can decrease the amount of free chlorine available in drinking water systems. The efficacy of 100 μg/L silver and 400 μg/L copper, individually and combined, were evaluated as secondary, longer-lasting residual disinfectants against Salmonella enterica serovar Typhimurium, Escherichia coli, Listeria monocytogenes, and Mycobacterium fortuitum at 24 °C and 4 °C. A >5.0-log reduction was observed in E. coli and L. monocytogenes after three hours and S. Typhimurium following seven hours of exposure to silver. M. fortuitum was the most resistant species to silver (1.11-log after seven hours). Copper did not significantly reduce S. Typhimurium and E. coli at 24 °C; ≥2.80-log reductions were observed in the Gram-positive L. monocytogenes and M. fortuitum. Longer exposure times were required at 4 °C to achieve significant reductions in all species. A synergistic effect was observed when silver and copper were combined at 24 °C. In addition, silver was not affected by the presence of organic matter at concentrations that completely inhibited 0.2 mg/L chlorine. The results of this study suggest that combinations of silver and copper show promise as secondary residual disinfectants. They may also be used in conjunction with low chlorine levels or other disinfectants to provide additional, long-lasting residuals in distribution systems.
• Verhougstraete, M. P., Gerald, J. K., Gerba, C. P., & Reynolds, K. A. (2019). Cost-benefit of point-of-use devices for lead reduction. Environmental research, 171, 260-265.
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  Lead exposure represents a significant human health concern that often occurs with little warning to the consumer. Water lead levels can be mitigated by point-of-use (POU) devices such as reverse osmosis, distillation, or activated carbon with lead reduction media.
• Xue, J., Schmitz, B. W., Caton, K., Zhang, B., Zabaleta, J., Garai, J., Taylor, C. M., Romanchishina, T., Gerba, C. P., Pepper, I. L., & Sherchan, S. P. (2019). Assessing the spatial and temporal variability of bacterial communities in two Bardenpho wastewater treatment systems via Illumina MiSeq sequencing. The Science of the total environment, 657, 1543-1552.
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  Next generation sequencing provides new insights into the diversity and ecophysiology of bacteria communities throughout wastewater treatment plants (WWTP), as well as the fate of pathogens in wastewater treatment system. In the present study, we investigated the bacterial communities and human-associated Bacteroidales (HF183) marker in two WWTPs in North America that utilize Bardenpho treatment processes. Although, most pathogens were eliminated during wastewater treatment, some pathogenic bacteria were still observed in final effluents. The HF183 genetic marker demonstrated significant reductions between influent and post-Bardenpho treated samples in each WWTP, which coincided with changes in bacteria relative abundances and community compositions. Consistent with previous studies, the major phyla in wastewater samples were predominantly comprised by Proteobacteria (with Gammaproteobacteria and Alphaproteobacteria among the top two classes), Actinobacteria, Bacteroidetes, and Firmicutes. Dominant genera were often members of Proteobacteria and Firmicutes, including several pathogens of public health concern, such as Pseudomonas, Serratia, Streptococcus, Mycobacterium and Arcobacter. Pearson correlations were calculated to observe the seasonal variation of relative abundances of gene sequences at different levels based on the monthly average temperature. These findings profile how changes in bacterial communities can function as a robust method for monitoring wastewater treatment quality and performance for public and environmental health purposes.
• Zhu, L., Torres, M., Betancourt, W. Q., Sharma, M., Micallef, S. A., Gerba, C., Sapkota, A. R., Sapkota, A., Parveen, S., Hashem, F., May, E., Kniel, K., Pop, M., & Ravishankar, S. (2019). Incidence of fecal indicator and pathogenic bacteria in reclaimed and return flow waters in Arizona, USA. Environmental research, 170, 122-127.
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  The quality of irrigation water used to cultivate produce that is consumed raw is an important issue with regard to food safety. In this study, the microbiological quality of potential irrigation water sources in Arizona was evaluated by testing for the presence of indicator and pathogenic bacteria. Reclaimed water samples were collected from two wastewater treatment plants and return flow samples were collected from two drainage canals and one return flow pond. Standard membrane filtration methods were used for detection of indicator bacteria. Water samples (n = 28) were filtered through cellulose ester membrane filters and bacterial populations were enumerated by placing the filters on selective agar. For detection of pathogens (Salmonella enterica, Listeria monocytogenes and Shiga toxin-producing E. coli (STEC)), water samples were filtered through Modified Moore swabs and enriched in Universal Pre-enrichment Broth, followed by selective enrichment broth for each pathogen. The enriched broth was streaked onto agar media selective for each pathogen. Presumptive colonies were confirmed by PCR/real-time PCR. Among the 14 reclaimed water samples from two sites, the ranges of recovered populations of E. coli, total coliforms, and enterococci were 0-1.3, 0.5-8.3 × 10, and 0-5.5 CFU/100 mL, respectively. No L. monocytogenes, Salmonella or STEC were found. In the 13 return flow water samples from 3 sites, the ranges of recovered populations of E. coli, total coliforms and enterococci were 1.9-5.3 × 10, 6.5 × 10-9.1 × 10, and 2.9-3.7× 10 CFU/100 mL, respectively. All samples were negative for L. monocytogenes. One (7.1%) of the return flow samples was positive for E. coli O145. Nine (64.3%) of the samples were positive for Salmonella. Both real-time PCR and culture-based methods were used for the detection of Salmonella and L. monocytogenes, and the results from the two methods were comparable. The findings of this study provide evidence that irrigation waters in Arizona, including reclaimed water and return flows, could be potential sources of bacterial contamination of produce. Additional work is needed to evaluate whether bacteria present in irrigation water sources transfer to the edible portion of irrigated plants and are capable of persisting through post-harvest activities.
• Betancourt, W. Q., Abd-Elmaksoud, S., & Gerba, C. P. (2018). Efficiency of Reovirus Concentration from Water with Positively Charged Filters. Food and environmental virology, 10(2), 209-211.
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  This study examined the efficacy of reovirus concentration from large volumes of water using two positively charged filters: Zeta Plus 1MDS and NanoCeram. The results indicated that an average of 61 and 81% of input reoviruses were effectively recovered, respectively, from recycled water and tap water using NanoCeram filtration.
• Gerba, C. P., Betancourt, W. Q., Kitajima, M., & Rock, C. M. (2018). Reducing uncertainty in estimating virus reduction by advanced water treatment processes. Water research, 133, 282-288.
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  Treatment of wastewater for potable reuse requires the reduction of enteric viruses to levels that pose no significant risk to human health. Advanced water treatment trains (e.g., chemical clarification, reverse osmosis, ultrafiltration, advanced oxidation) have been developed to provide reductions of viruses to differing levels of regulatory control depending upon the levels of human exposure and associated health risks. Importance in any assessment is information on the concentration and types of viruses in the untreated wastewater, as well as the degree of removal by each treatment process. However, it is critical that the uncertainty associated with virus concentration and removal or inactivation by wastewater treatment be understood to improve these estimates and identifying research needs. We reviewed the critically literature to assess to identify uncertainty in these estimates. Biological diversity within families and genera of viruses (e.g. enteroviruses, rotaviruses, adenoviruses, reoviruses, noroviruses) and specific virus types (e.g. serotypes or genotypes) creates the greatest uncertainty. These aspects affect the methods for detection and quantification of viruses and anticipated removal efficiency by treatment processes. Approaches to reduce uncertainty may include; 1) inclusion of a virus indicator for assessing efficiency of virus concentration and detection by molecular methods for each sample, 2) use of viruses most resistant to individual treatment processes (e.g. adenoviruses for UV light disinfection and reoviruses for chlorination), 3) data on ratio of virion or genome copies to infectivity in untreated wastewater, and 4) assessment of virus removal at field scale treatment systems to verify laboratory and pilot plant data for virus removal.
• Gerba, C. P., Lopez, G. U., Abd-Elmaksoud, S., Wissler, A., Sifuentes, L., & Mitchell, J. (2018). Modeling of ultraviolet light inactivation kinetics of methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, Clostridium difficile spores and murine norovirus on fomite surfaces. Journal of Applied Microbiology. doi:10.1111/jam.14103
• Gerba, C. P., Mclain, J. E., Bright, K., Carr, D., Brassill, N. A., & Rock, C. M. (2018). Review of water quality criteria for water reuse and risk-based implications for irrigated produce under the FDA Food Safety Modernization Act, Produce Safety Rule. Environmental Research, 172, 616-629. doi:10.1016/j.envres.2018.12.050
• Hata, A., Kitajima, M., Haramoto, E., Lee, S., Ihara, M., Gerba, C. P., & Tanaka, H. (2018). Next-generation amplicon sequencing identifies genetically diverse human astroviruses, including recombinant strains, in environmental waters. Scientific reports, 8(1), 11837.
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  Human astroviruses are associated with gastroenteritis and known to contaminate water environments. Three different genetic clades of astroviruses are known to infect humans and each clade consists of diverse strains. This study aimed to determine the occurrence and genetic diversity of astrovirus strains in water samples in different geographical locations, i.e., influent and effluent wastewater samples (n = 24 each) in Arizona, U.S., and groundwater (n = 37) and river water (n = 14) samples collected in the Kathmandu Valley, Nepal, using next-generation amplicon sequencing. Astrovirus strains including rare types (types 6 and 7 classical human astroviruses), emerging type (type 5 VA-astroviruses), and putative recombinants were identified. Feline astrovirus strains were collaterally identified and recombination between human and feline astroviruses was suggested. Classical- and VA-astroviruses seemed to be prevalent during cooler months, while MLB-astroviruses were identified only during warmer months. This study demonstrated the effectiveness of next-generation amplicon sequencing for identification and characterization of genetically diverse astrovirus strains in environmental water.
• Masaaki, K., Walter, B., Gerba, C. P., & Rock, C. M. (2018). Reducing uncertainty in estimating virus reduction by advanced water treatment processes.
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  Treatment of wastewater for potable reuse requires the reduction of enteric viruses to levels that pose nosignificant risk to human health. Advanced water treatment trains (e.g., chemical clarification, reverseosmosis, ultrafiltration, advanced oxidation) have been developed to provide reductions of viruses todiffering levels of regulatory control depending upon the levels of human exposure and associated healthrisks. Importance in any assessment is information on the concentration and types of viruses in theuntreated wastewater, as well as the degree of removal by each treatment process. However, it is criticalthat the uncertainty associated with virus concentration and removal or inactivation by wastewatertreatment be understood to improve these estimates and identifying research needs. We reviewed thecritically literature to assess to identify uncertainty in these estimates. Biological diversity within familiesand genera of viruses (e.g. enteroviruses, rotaviruses, adenoviruses, reoviruses, noroviruses) and specificvirus types (e.g. serotypes or genotypes) creates the greatest uncertainty. These aspects affect themethods for detection and quantification of viruses and anticipated removal efficiency by treatmentprocesses. Approaches to reduce uncertainty may include; 1) inclusion of a virus indicator for assessingefficiency of virus concentration and detection by molecular methods for each sample, 2) use of virusesmost resistant to individual treatment processes (e.g. adenoviruses for UV light disinfection and reovirusesfor chlorination), 3) data on ratio of virion or genome copies to infectivity in untreated wastewater,and 4) assessment of virus removal at field scale treatment systems to verify laboratory and pilot plantdata for virus removal.
• Pepper, I. L., & Gerba, C. P. (2018). Risk of infection from Legionella associated with spray irrigation of reclaimed water. Water research, 139, 101-107.
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  Legionella pneumophila has been detected in reclaimed water used for spray irrigation of turfgrass in public parks and golf courses. This study determined the risks of infection from exposure to various levels of Legionella in reclaimed waters considering: the method of spray application; and the duration and frequency of exposure. Evaluation of these factors resulted in a risk of infection greater than 1:10,000 for several scenarios when the number of Legionella in the reclaimed water exceeded 1000 colony-forming units (CFU) per ml. Most current guidelines for control of Legionella in distribution systems recommend that increased monitoring or remedial action be taken when Legionella levels exceed 1000 to 10,000 CFU/ml. Based upon our risk assessment, these guidelines seem appropriate for reclaimed water systems where spray irrigation is practiced.
• Pepper, I. L., Brooks, J. P., & Gerba, C. P. (2018). Antibiotic Resistant Bacteria in Municipal Wastes: Is There Reason for Concern?. Environmental science & technology, 52(7), 3949-3959.
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  Recently, there has been increased concern about the presence of antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARG), in treated domestic wastewaters, animal manures and municipal biosolids. The concern is whether these additional sources of ARB contribute to antibiotic resistance levels in the environment, that is, "environmental antibiotic resistance." ARB and ARG occur naturally in soil and water, and it remains unclear whether the introduction of ARB in liquid and solid municipal and animal wastes via land application have any significant impact on the background levels of antibiotic resistance in the environment, and whether they affect human exposure to ARB. In this current review, we examine and re-evaluate the incidence of ARB and ARG resulting from land application activities, and offer a new perspective on the threat of antibiotic resistance to public health via exposure from nonclinical environmental sources. Based on inputs of ARBs and ARGs from land application, their fate in soil due to soil microbial ecology principles, and background indigenous levels of ARBs and ARGs already present in soil, we conclude that while antibiotic resistance levels in soil are increased temporally by land application of wastes, their persistence is not guaranteed and is in fact variable, and often contradictory based on application site. Furthermore, the application of wastes may not produce the most direct impact of ARGs and ARB on public health. Further investigation is still warranted in agriculture and public health, including continued scrutiny of antibiotic use in both sectors.
• Reynolds, K. A., Gerba, C. P., Gerald, J. K., & Verhougstraete, M. (2019). Cost-benefit of point-of-use devices for lead reduction. Environmental Research.
• Sassi, H. P., Abd-Elmaksoud, S., Gerba, C. P., Pepper, I. L., & Ikner, L. A. (2018). Comparative survival of viruses during thermophilic and mesophilic anaerobic digestion.. Science of The Total Environment.
• Sassi, H. P., Ikner, L. A., Abd-Elmaksoud, S., Gerba, C. P., & Pepper, I. L. (2018). Comparative survival of viruses during thermophilic and mesophilic anaerobic digestion. The Science of the total environment, 615, 15-19.
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  Micro-scale technology was used to obtain survival data for three animal viruses and two bacteriophages during anaerobic digestion. The data for adenoviruses, MS2 and Φ6 provide the first published reports for survival of these viruses during mesophilic anaerobic digestion. Data were also obtained for thermophilic digestion, which showed greater inactivation of viruses at the higher temperature. Data on the survival of Φ6 are of particular interest since it is a lipid-based virus which has been suggested as a surrogate for the Ebola virus. In contrast, MS2 was found to be an inappropriate surrogate for Ebola.
• Sassi, H. P., Reynolds, K. A., Pepper, I. L., & Gerba, C. P. (2018). Evaluation of hospital-grade disinfectants on viral deposition on surfaces after toilet flushing. American journal of infection control, 46(5), 507-511.
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  Past studies have shown that infectious aerosols created during toilet flushing result in surface contamination of the restroom. The goals of this study were to quantify viral contamination of surfaces in restrooms after flushing and the impact of disinfectants added to the toilet bowl prior to flushing on reducing surface contamination.
• Sassi, H. P., Tuttle, K. D., Betancourt, W. Q., Kitajima, M., & Gerba, C. P. (2018). Persistence of Viruses by qPCR Downstream of Three Effluent-Dominated Rivers in the Western United States. Food and environmental virology, 10(3), 297-304.
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  This study was designed to determine the quantitative polymerase chain reaction (qPCR) signal persistence of viruses in three effluent-dominated streams. Samples were collected from the effluent outfall of three wastewater treatment plants in the Western United States and downstream at different locations. All samples were tested for the presence of pepper mild mottle virus (PMMoV), adenoviruses, norovirus GI and GII, Aichi virus, and enteroviruses using qPCR. PMMoV was detected most frequently in 54/57 (94.7%) samples, followed by adenoviruses which was detected in 21/57 (36.8%) samples. PMMoV was detected at all locations downstream and up to 32 km from the discharge point. This study demonstrated that the detection signal of PMMoV was able to persist in wastewater discharges to a greater degree than human enteric viruses in effluent-dominated rivers.
• Schaffner, D. W., Jensen, D., Gerba, C. P., Shumaker, D., & Arbogast, J. W. (2018). Influence of Soap Characteristics and Food Service Facility Type on the Degree of Bacterial Contamination of Open, Refillable Bulk Soaps. Journal of food protection, 81(2), 218-225.
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  Concern has been raised regarding the public health risks from refillable bulk-soap dispensers because they provide an environment for potentially pathogenic bacteria to grow. This study surveyed the microbial quality of open refillable bulk soap in four different food establishment types in three states. Two hundred ninety-six samples of bulk soap were collected from food service establishments in Arizona, New Jersey, and Ohio. Samples were tested for total heterotrophic viable bacteria, Pseudomonas, coliforms and Escherichia coli, and Salmonella. Bacteria were screened for antibiotic resistance. The pH, solids content, and water activity of all soap samples were measured. Samples were assayed for the presence of the common antibacterial agents triclosan and parachlorometaxylenol. More than 85% of the soap samples tested contained no detectable microorganisms, but when a sample contained any detectable microorganisms, it was most likely contaminated at a very high level (∼7 log CFU/mL). Microorganisms detected in contaminated soap included Klebsiella oxytoca, Serratia liquefaciens, Shigella sonnei, Enterobacter gergoviae, Serratia odorifera, and Enterobacter cloacae. Twenty-three samples contained antibiotic-resistant organisms, some of which were resistant to two or more antibiotics. Every sample containing less than 4% solids had some detectable level of bacteria, whereas no samples with greater than 14% solids had detectable bacteria. This finding suggests the use of dilution and/or low-cost formulations as a cause of bacterial growth. There was a statistically significant difference ( P = 0.0035) between the fraction of bacteria-positive samples with no detected antimicrobial agent (17%) and those containing an antimicrobial agent (7%). Fast food operations and grocery stores were more likely to have detectable bacteria in bulk-soap samples compared with convenience stores ( P < 0.05). Our findings underscore the risk to public health from use of refillable bulk-soap dispensers in food service establishments.
• Schmitz, B. W., Moriyama, H., Haramoto, E., Kitajima, M., Sherchan, S., Gerba, C. P., & Pepper, I. L. (2018). Reduction of Cryptosporidium, Giardia, and Fecal Indicators by Bardenpho Wastewater Treatment. Environmental science & technology, 52(12), 7015-7023.
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  Increased demand for water reuse and reclamation accentuates the importance for optimal wastewater treatment to limit protozoa in effluents. Two wastewater treatment plants utilizing advanced Bardenpho were investigated over a 12-month period to determine the incidence and reduction of Cryptosporidium, Giardia, Cyclospora, and fecal indicators. Results were compared to facilities that previously operated in the same geographical area. Protozoa (oo)cysts were concentrated using an electronegative filter and subsequently detected by fluorescent microscopy and/or PCR methods. Cryptosporidium and Giardia were frequently detected in raw sewage, but Cyclospora was not detected in any wastewater samples. Facilities with Bardenpho treatment exhibited higher removals of (oo)cysts than facilities utilizing activated sludge or trickling filters. This was likely due to Bardenpho systems having increased solid wasting rates; however, this mechanism cannot be confirmed as sludge samples were not analyzed. Use of dissolved-air-flotation instead of sedimentation tanks did not result in more efficient removal of (oo)cysts. Concentrations of protozoa were compared with each other, Escherichia coli, somatic coliphage, and viruses (pepper mild mottle virus, Aichi virus 1, adenovirus, and polyomaviruses JC and BK). Although significant correlations were rare, somatic coliphage showed the highest potential as an indicator for the abundance of protozoa in wastewaters.
• Verhougstraete, M., Reynolds, K. A., & Gerba, C. P. (2017). Lead in drinking water: Point of use cost benefit analysis.. Environmental Health Perspectives.
• Gerba, C. P. (2017). A comparison of urethane and cellulose sponges as cleaning tools in household kitchens. Food Protection Trends, 27, 170-175.
• Gerba, C. P. (2017). Review: Occurrence of the pathogenic amoeba Naegleria fowleri in groundwater.. Journal of Hydeogeology, 25, 953-958.
• Gerba, C. P., & Betancourt, W. (2017). Viral aggregation: impact on virus behavior in the environment.. Environmental Sceince and Technology, 51, 7316-7325.
• Gerba, C. P., & Bright, K. R. (2017). Review: Occurrence of the pathogenic amoeba Naegleria fowleri in groundwater. HYDROGEOLOGY JOURNAL, 25(4), 953-958. doi:https://doi.org/10.1007/s10040-017-1582-4
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  Naegleria fowleri is a thermophilic free-livingamoeba found worldwide in soils and warm freshwater. It isthe causative agent of primary amebic meningoencephalitis, anearly always fatal disease afflicting mainly children andyoung adults. Humans are exposed to the organism via swimming,bathing, or other recreational activity during which wateris forcefully inhaled into the upper nasal passages.Although many studies have looked at the occurrence ofN. fowleri in surface waters, limited information is availableregarding its occurrence in groundwater and geothermallyheated natural waters such as hot springs. This paper reviewsthe current literature related to the occurrence of N. fowleri inthese waters and the methods employed for its detection. Casereports of potential groundwater exposures are also included.Despite increased interest in N. fowleri in recent years due towell-publicized cases linked to drinking water, many questionsstill remain unanswered. For instance, why the organismpersists in some water sources and not in others is not wellunderstood. The role of biofilms in groundwater wells andplumbing in individual buildings, and the potential forwarming due to climate change to expand the occurrence ofthe organism into new regions, are still unclear. Additionalresearch is needed to address these questions in order to betterunderstand the ecology of N. fowleri and the conditions thatresult in greater risks to bathers.
• Kitajima, M., Iker, B., Magill-Collins, A., Gaither, M., Stoehr, J. D., & Gerba, C. P. (2017). Genetic analysis of norovirus strains caused gastroenteritis outbreaks among river rafters in the Grand Canyon, Arizona. Food and Environmental Virology, 9, 238-240.
• Regnery, J., Gerba, C. P., Dickenson, E., & Drewes, J. R. (2017). The importance of key attenuation factors for microbial and chemical contaminates during managed aquifer recharge: a review. Crit. Rev. Environ. Sci. Technol., 47, 1409-1452.
• Reynolds, K. A., & Gerba, C. P. (2017). Quantifying the impact of hygiene interventions. Household and Personal Care Products, 12, 12-14.
• Rosiles-González, G., Ávila-Torres, G., Moreno-Valenzuela, O., Acosta-González, G., . Leal-Bautista, R., Grimaldo-Hernández, D., Betancourt, W., Gerba, C. P., & Hernández-Zepeda, C. (2017). Occurrence of Pepper Mild Mottle Virus (PMMoV) in Groundwater from a Karst Aquifer System in the Yucatan Peninsula, Mexico. Food and Environmental Virology, 9, 487-497.
• Sassi, H., Ikner, L. A., Abd-Elmaksoud, A., Gerba, C. P., & Pepper, I. L. (2017). Comparative survival of viruses during thermophilic and mesophilic anaerobic digestion. Sci. Total Environ, 615, 15-19.
• Sifuentes, L. Y., Maxwell, S., Gerba, C. P., Reynolds, K. A., Tamimi, A., & Koenig, D. (2017). Use of ATP Readings to Predict a Successful Hygiene Intervention in the Workplace. Food and Environmental Virology, 9, 14-19.
• Tamrakar, S. B., Henley, J., Gurian, P. L., Gerba, C. P., Mitchell, J., Enger, K., & Rose, J. B. (2017). Persistence analysis of poliovirus on three different types of fomites. Journal of applied microbiology, 122(2), 522-530.
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  The goal of this study was to explore various models for describing viral persistence (infectivity) on fomites and identify the best fit models.
• Zhou, K., Sassi, H., Morrision, C., Duan, J. G., & Gerba, C. P. (2017). Resuspension of Escherichia coli and MS2 bacteriophage from bed sediment in irrigation canals. J. Irrigation and Drainage Engineering. doi:DOI:10.1061/(ASCE)IR.1943-4774.0001169
• Betancourt, W. Q., & Gerba, C. P. (2016). Rethinking the Significance of Reovirus in Water and Wastewater. Food and environmental virology, 8(3), 161-73.
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  The genus Orthoreovirus contains nonenveloped viruses with double-stranded gene segments encased in a double-layered icosahedral capsid shell. These features constitute major determinants of virion stability in the environment and virion resistance against physical and chemical agents. Reovirus (ReoV) is the general term most commonly used for all virus strains that infect humans and nonhuman animals. Several studies have demonstrated the frequent occurrence of ReoV in wastewaters and natural waters, including surface and ground waters from different geographical areas. Most of these studies have reported higher concentrations of ReoV than any other enteric virus analyzed. They are more commonly isolated in chlorine-disinfected wastewaters than other enteric viruses, and appear to survive longer in water. The ability of ReoV to form large aggregates, even with different types of enteric viruses (e.g., poliovirus) and their ability to undergo mechanisms of gene segment reassortment among different serotypes may also explain their greater stability. Different approaches have been applied for concentration of ReoV from water; however, the recovery efficiency of the filtration methods has not been fully evaluated. Recently, molecular methods for identification of ReoV strains and quantification of virus genome have been developed. Studies have shown that the overall detection sensitivity of ReoV RNA is enhanced through initial replication of infectious virions in cell culture. More studies are needed to specifically address unresolved issues about the fate and distribution of ReoV in the environment since this virus is not commonly included in virological investigations.
• Chaidez, C., Ibarra-Rodríguez, J. R., Valdez-Torres, J. B., Soto, M., Gerba, C. P., & Castro-Del Campo, N. (2016). Point-of-use Unit Based on Gravity Ultrafiltration Removes Waterborne Gastrointestinal Pathogens from Untreated Water Sources in Rural Communities. Wilderness & environmental medicine, 27(3), 379-85.
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  In developing countries, rural communities often face the lack of potable water infrastructure and must rely on untreated sources for drinking, which are often contaminated with waterborne pathogens. The use of home water treatment devices is seen as one means of reducing the risk of exposure to waterborne pathogens. The aim of this study was to evaluate the microbiological and physicochemical performance of a simple in-home point-of-use device based on gravity ultrafiltration through an ultrafilter membrane.
• Gerba, C. P. (2016). Biosolids application for barley production. J. Residual Science and Technol., 13, 153-163.
• Gerba, C. P. (2016). Genomic analysis of broad-host-range Enterobacteriophage Av-05. Genome Announc, 11(3), pii: e00282-15.. doi:10.1128/genomeA.00282-15
• Gerba, C. P., Lopez, G. U., & Ikner, L. A. (2016). Distribution of Bacteria in Dental Offices and the Impact of Hydrogen Peroxide Disinfecting Wipes. Journal of dental hygiene : JDH, 90(6), 354-361.
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  The purpose of this study was to characterize the occurrence of heterotrophic plate count bacteria (HPCs), fecal bacterial indicators, and methicillin-resistant Staphylococcus aureus (MRSA) on hard, nonporous surfaces (fomites) commonly found in dental offices, and to assess the impact of a hygienic disinfection intervention on the reduction of these bacteria in the office setting. Samples of various fomites were collected from dental offices located in Arizona (6) and Illinois (4) and assayed for HPCs, total coliforms, Escherichia coli, and MRSA in order to establish baseline bacterial levels. Dental office personnel were then provided with disposable disinfectant wipes containing hydrogen peroxide to use in the office, and the surfaces were subsequently resampled to assess their impact on the specified bacterial populations. The greatest numbers of HPCs were found on the patients' arm rest and office phones, with dental tool handles and the dentist examination lights yielding the lowest levels. Coliform bacteria and E. coli were also detected on those surfaces demonstrating the highest HPCs, and were cultured from other fomites as well. MRSA was also isolated from 5% of the fomites tested. The use of disinfectant wipes significantly reduced the numbers of HPC bacteria detected on fomites (p=0.002). No total coliforms, E. coli, or MRSA were cultured from disinfected fomites following the hygienic intervention. The use of hydrogen peroxide-impregnated towelettes reduced total bacterial numbers on fomites commonly located in dental offices. Total coliforms, E. coli, and MRSA were reduced to levels below detection.
• Gerba, C. P., Sifuentes, L. Y., Lopez, G. U., Abd-Elmaksoud, S., Calabrese, J., & Tanner, B. (2016). Wide-spectrum activity of a silver-impregnated fabric. American journal of infection control, 44(6), 689-90.
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  Fabrics, such as clothing, drapes, pillowcases, and bedsheets are potential sources of pathogenic bacteria and viruses. We found fabrics (ie, professional clothing, pillowcases, and lab coats) treated with a silver-impregnated material to be effective in significantly reducing a wide spectrum of ordinary and drug-resistant microorganisms, including Salmonella, methicillin-resistant Staphylococcus aureus, Propionibacterium acnes, Trichphyton mentagrophytes, and norovirus. Fabrics impregnated with antimicrobial agents help provide an additional barrier to the transport or reservoir of pathogens in health care environments.
• Gerba, C. P., Wuollet, A. L., Raisanen, P., & Lopez, G. U. (2016). Bacterial contamination of computer touch screens. American journal of infection control, 44(3), 358-60.
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  The goal of this study was to determine the occurrence of opportunistic bacterial pathogens on the surfaces of computer touch screens used in hospitals and grocery stores. Opportunistic pathogenic bacteria were isolated on touch screens in hospitals; Clostridium difficile and vancomycin-resistant Enterococcus and in grocery stores; methicillin-resistant Staphylococcus aureus. Enteric bacteria were more common on grocery store touch screens than on hospital computer touch screens.
• Kitajima, M., Rachmadi, A. T., Iker, B. C., Haramoto, E., & Gerba, C. P. (2016). Genetically distinct genogroup IV norovirus strains identified in wastewater. Archives of virology, 161(12), 3521-3525.
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  We investigated the prevalence and genetic diversity of genogroup IV norovirus (GIV NoV) strains in wastewater in Arizona, United States, over a 13-month period. Among 50 wastewater samples tested, GIV NoVs were identified in 13 (26 %) of the samples. A total of 47 different GIV NoV strains were identified, which were classified into two genetically distinct clusters: the GIV.1 human cluster and a unique genetic cluster closely related to strains previously identified in Japanese wastewater. The results provide additional evidence of the considerable genetic diversity among GIV NoV strains through the analysis of wastewater containing virus strains shed from all populations.
• Lopez, G. U., Gerba, C. P., Ikner, L. A., Lopez, G. U., Gerba, C. P., & Ikner, L. A. (2016). Distribution of Bacteria in Dental Offices and the Impact of Hydrogen Peroxide Disinfecting Wipes. The Journal of Dental Hygiene, 90(6), 354-361.
• Rachmadi, A. T., Kitajima, M., Pepper, I. L., & Gerba, C. P. (2016). Enteric and indicator virus removal by surface flow wetlands. The Science of the total environment, 542(Pt A), 976-82.
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  We investigated the occurrence and attenuation of several human enteric viruses (i.e., norovirus, adenovirus, Aichi virus 1, polyomaviruses, and enterovirus) as well as a plant virus, pepper mild mottle virus (PMMoV), at two surface flow wetlands in Arizona. The retention time in one of the wetlands was seven days, whereas in the other wetland it could not be defined. Water samples were collected at the inlet and outlet from the wetlands over nine months, and concentration of viral genomes was determined by quantitative polymerase chain reaction (qPCR). Of the human enteric viruses tested, adenovirus and Aichi virus 1 were found in the greatest prevalence in treated wastewater (i.e., inlet of the wetlands). Reduction efficiencies of enteric viruses by the wetlands ranged from 1 to 3 log10. Polyomaviruses were generally removed to below detection limit, indicating at least 2 to 4 log10 removal. PMMoV was detected in a greater concentration in the inlet of both wetlands for all the viruses tested (10(4) to 10(7) genome copies/L), but exhibited little or no removal (1 log10 or less). To determine the factors associated with virus genome attenuation (as determined by qPCR), the persistence of PMMoV and poliovirus type 1 (an enterovirus) was studied in autoclaved and natural wetland water, and deionized water incubated under three different temperatures for 21 days. A combination of elevated water temperature and biological activities reduced poliovirus by 1 to 4 log10, while PMMoV was not significantly reduced during this time period. Overall, PMMoV showed much greater persistence than human viruses in the wetland treatment.
• Reynolds, K. A., Beamer, P. -., Plotkin, K. R., Sifuentes, L. Y., Koenig, D. W., & Gerba, C. P. (2014). The Healthy Workplace Project: Reduced Viral Exposure in an Office Setting. Archives of Environmental and Occupational Health.
• Reynolds, K. A., Beamer, P. I., Plotkin, K. R., Sifuentes, L. Y., Koenig, D. W., & Gerba, C. P. (2016). The healthy workplace project: Reduced viral exposure in an office setting. Archives of environmental & occupational health, 71(3), 157-62.
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  Viral illnesses such as gastroenteritis and the common cold create a substantial burden in the workplace due to reduced productivity, increased absenteeism, and increased health care costs. Behaviors in the workplace contribute to the spread of human viruses via direct contact between hands, contaminated surfaces, and the mouth, eyes, and/or nose. This study assessed whether implementation of the Healthy Workplace Project (HWP) (providing hand sanitizers, disinfecting wipes, facial tissues, and use instructions) would reduce viral loads in an office setting of approximately 80 employees after seeding fomites and the hands of volunteer participants with an MS-2 phage tracer. The HWP significantly reduced viable phage detected on participants' hands, communal fomites, and personal fomites (p ≤ .010) in office environments and presents a cost-effective method for reducing the health and economic burden associated with viral illnesses in the workplace.
• Schmitz, B. W., Kitajima, M., Campillo, M. E., Gerba, C. P., & Pepper, I. L. (2016). Virus Reduction during Advanced Bardenpho and Conventional Wastewater Treatment Processes. Environmental science & technology, 50(17), 9524-32.
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  The present study investigated wastewater treatment for the removal of 11 different virus types (pepper mild mottle virus; Aichi virus; genogroup I, II, and IV noroviruses; enterovirus; sapovirus; group-A rotavirus; adenovirus; and JC and BK polyomaviruses) by two wastewater treatment facilities utilizing advanced Bardenpho technology and compared the results with conventional treatment processes. To our knowledge, this is the first study comparing full-scale treatment processes that all received sewage influent from the same region. The incidence of viruses in wastewater was assessed with respect to absolute abundance, occurrence, and reduction in monthly samples collected throughout a 12 month period in southern Arizona. Samples were concentrated via an electronegative filter method and quantified using TaqMan-based quantitative polymerase chain reaction (qPCR). Results suggest that Plant D, utilizing an advanced Bardenpho process as secondary treatment, effectively reduced pathogenic viruses better than facilities using conventional processes. However, the absence of cell-culture assays did not allow an accurate assessment of infective viruses. On the basis of these data, the Aichi virus is suggested as a conservative viral marker for adequate wastewater treatment, as it most often showed the best correlation coefficients to viral pathogens, was always detected at higher concentrations, and may overestimate the potential virus risk.
• Sifuentes, L. Y., Fankem, S. L., Reynolds, K., Tamimi, A. H., Gerba, C. P., & Koenig, D. (2016). Use of ATP Readings to Predict a Successful Hygiene Intervention in the Workplace to Reduce the Spread of Viruses on Fomites. Food and environmental virology.
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  The purpose of this study was to validate the use of adenosine triphosphate (ATP) for evaluating hygiene intervention effectiveness in reducing viral dissemination in an office environment. The bacterial virus MS-2 was used to evaluate two scenarios, one where the hand of an individual was contaminated and another where a fomite was contaminated. MS-2 was selected as a model because its shape and size are similar to many human pathogenic viruses. Two separate experiments were conducted, one in which the entrance door push plate was inoculated and the other in which the hand of one selected employee was inoculated. In both scenarios, 54 selected surfaces in the office were tested to assess the dissemination of the virus within the office. Associated surface contamination was also measured employing an ATP meter. More than half of the tested hands and surfaces in the office were contaminated with MS-2 within 4 h. Next, an intervention was conducted, and each scenario was repeated. Half of the participating employees were provided hand sanitizer, facial tissues, and disinfecting wipes, and were instructed in their use. A significant (p 
• Suppes, L. M., Canales, R. A., Gerba, C. P., & Reynolds, K. A. (2016). Cryptosporidium risk from swimming pool exposures. International journal of hygiene and environmental health, 219(8), 915-919.
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  Infection risk estimates from swimming in treated recreational water venues are lacking and needed to prioritize public health interventions in swimming pools. Quantitative infection risk estimates among different age groups are needed to identify vulnerable populations. High risk populations can be targeted during public health interventions, like education campaigns and pool operation improvements.
• Suppes, L., Canales, R. A., Gerba, C. P., & Reynolds, K. A. (2014). Cryptosporidium risk from swimming pool exposures. International Journal of Hygiene and Environmental Health.
• Suppes, L., Canales, R. A., Gerba, C. P., & Reynolds, K. A. (2014). Risk Assessment of Cryptosporidiosis among Recreational Swimmers in the United States. International Journal of Hygiene and Environmental Health, 219, 915-919.
• Suppes, L., Canales, R. A., Gerba, C. P., & Reynolds, K. A. (2016). Cryptosporidium risk from swimming pool exposures. International Journal of Hygiene and Environmental Health.
• Beamer, P. -., Plotkin, K. R., Gerba, C. P., Sifuentes, L. Y., Koenig, D. W., & Reynolds, K. A. (2015). Modeling of Human Viruses on Hands and Risk of Infection in an Office Workplace using Micro-Activity Data. Journal of Occupational and Environmental Hygiene, 12(4), 266-275.
• Beamer, P. I., Plotkin, K. R., Gerba, C. P., Sifuentes, L. Y., Koenig, D. W., & Reynolds, K. A. (2015). Modeling of Human Viruses on Hands and Risk of Infection in an Office Workplace Using Micro-Activity Data. JOURNAL OF OCCUPATIONAL AND ENVIRONMENTAL HYGIENE, 12(4), 266-275.
• Beltran, M. S., Gerba, C. P., Fett, A. P., Luchansky, J. B., & Chaidez, C. (2015). Prevalence and characterization of Listeria monocytogenes, Salmonella and Shiga toxin-producing Escherichia coli isolated from small Mexican retail markets of queso fresco. INTERNATIONAL JOURNAL OF ENVIRONMENTAL HEALTH RESEARCH, 25(2), 140-148.
• Gerba, C. P. (2015). Aichi virus 1: Environmental occurrence and behavior. Pathogens, 4, 254-268.
• Gerba, C. P. (2015). Use of an ultraviolet light at point-of-dispense faucet to eliminate Pseudomonas aeruginosa. AMERICAN JOURNAL OF INFECTION CONTROL, 43(5), 528-529.
• Gerba, C. P., Abd-Elmaksoud, S., Newick, H., El-Esnawy, N. A., Barakat, A., & Ghanem, H. (2015). Assessment of Coliphage Surrogates for Testing Drinking Water Treatment Devices. FOOD AND ENVIRONMENTAL VIROLOGY, 7(1), 27-31.
• Gerba, C. P., Tamimi, A. H., Maxwell, S., & Edmonds, S. (2015). Impact of an alcohol-based hand sanitizer in the home on reduction in probability of infection by respiratory and enteric viruses. Epidemiology and Infection, 143, 3335-3341.
• Gerba, C. P., Wuollet, A. L., Raisanen, P. K., Lopez, G. U., Gerba, C. P., Wuollet, A. L., Raisanen, P. K., & Lopez, G. U. (2015). Bacterial Contamination of Computer Touch Screens. American Journal of Infection Control, 44(3), 358-360. doi:10.1016/j.ajic.2015.10.013
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  The goal of this study was to determine the occurrence of opportunistic bacterial pathogens on the surfaces of computer touch screens used in hospitals and grocery stores. Opportunistic pathogenic bacteriawere isolated on touch screens in hospitals; Clostridium difficile and vancomycin-resistant Enterococcus and in grocery stores; methicillin-resistant Staphylococcus aureus. Enteric bacteria were more common on grocery store touch screens than on hospital computer touch screens.
• Kitajima, M., Rachmadi, A. T., Iker, B. C., Haramoto, E., Pepper, I. L., & Gerba, C. P. (2015). Occurrence and genetic diversity of human cosavirus in influent and effluent of wastewater treatment plants in Arizona, United States. ARCHIVES OF VIROLOGY, 160(7), 1775-1779.
• Lopez, G. U., Kitajima, M., Sexton, J. D., Gerba, C. P., & Reynolds, K. A. (2015). Risk of Campylobacter jejuni Infection from Preparing Raw Chicken in Domestic Kitchens and Reduction of Cross-contamination Using Disinfectant Wipes. Journal of Applied Microbiology, 119, 245-252.
• Lopez, G. U., Kitajima, M., Sherchan, S. O., Sexton, J. D., Sifuentes, L. Y., Gerba, C. P., & Reynolds, K. A. (2015). Impact of disinfectant wipes on the risk of Campylobacter jejuni infection during raw chicken preparation in domestic kitchens. Applied and Environmental Microbiology, 119, 245-252.
• Lopez, G. u., Katajima, M., Sherchan, S. P., Sexton, J. D., Gerba, C. P., Reynolds, K. A., Lopez, G. u., Katajima, M., Sherchan, S. P., Sexton, J. D., Gerba, C. P., & Reynolds, K. A. (2015). Impact of Disinfectant Wipes on the Risk of Campylobacter jejuni Infection During Raw Chicken Preparation in Domestic Kitchens. Journal of Applied Microbiology. doi:10.1111/jam.12834 [Epub ahead of print]
• Lopez-Cuevas, O., Castro-Del Camp, N., Gerba, C. P., Amarillas, L., & Chadidez, C. C. (2015). Genomic Analysis of Broad-Host-Range Enterobacteriophage Av-05. Genome Annoucements, 3(3), pii: e00282-15. doi:10.1128/genomeA.00282-15
• Magill-Collins, A., Gaither, M., Gerba, C. P., Kitajima, M., Iker, B. C., & Stoehr, J. D. (2015). Norovirus Outbreaks Among Colorado River Rafters in the Grand Canyon, Summer 2012. WILDERNESS & ENVIRONMENTAL MEDICINE, 26(3), 312-318.
• Reynolds, K. A., Beamer, P. -., Plotkin, K. R., Sifuentes, L. Y., Koenig, D. W., & Gerba, C. P. (2015). The Healthy Workplace Project: Reduced Viral Exposure in an Office Setting. Archives of Environmental and Occupational Health, doi:10.1080/19338244.2015.1058234.
• Sassi, H. P., Sifuentes, L. Y., Koenig, D. W., Nichols, E., Clark-Greuel, J., Wong, L. F., McGrath, K., Gerba, C. P., & Reynolds, K. A. (2015). Control of the spread of viruses in a long-term care facility using hygiene protocols. AMERICAN JOURNAL OF INFECTION CONTROL, 43(7), 702-706.
• Song, I., O'Shaughnessy, S. A., Choi, C. Y., & Gerba, C. P. (2015). Impacts of tilling and covering treatments on the biosolids solar drying conversion from class B to class A. Environmental technology, 35(17-20), 2610-8.
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  The objective of this study was to evaluate the effects of tillage and cover treatments of solar drying on the conversion of class B treated sewage sludge to a class A product. The experiments were performed over two years at Green Valley, Arizona in steel-constructed sand-filled drying beds of 1.0 m (width) x 3.0 m (length) x 0.6 m (depth). Freshly produced aerobically and anaerobically digested biosolids from nearby wastewater treatment plants received tillage and cover treatments for expediting solar drying and microbial inactivation. During the summer drying, covered drying bed increased faecal inactivation rate by 26% over other treatments and automated rain shield abated faecal coliform regrowth from summer rains. Tilling accelerated evaporation of moisture from the biosolids and increased the inactivation rate of faecal coliforms during the summer season. An automated retractable roof to protect the biosolids from rain aided in maintaining class A criteria by preventing dried biosolids from re-wetting by rainfall. However, results from tilling and passive solar heating during the cold winter seasons did not improve the faecal coliform inactivation rate due mainly to lower ambient temperatures. Thus, tilling and cover treatments can be effective in accelerating biosolids solar drying and thus enhancing pathogen inactivation during the summer season. Investigation on the effects of tillage depth and frequency is recommended to determine optimal tilling practice.
• Tamimi, A. H., Edmonds-Wilson, S. L., & Gerba, C. P. (2015). Use of a Hand Sanitizing Wipe for Reducing Risk of Viral Illness in the Home. FOOD AND ENVIRONMENTAL VIROLOGY, 7(4), 354-358.
• Abd-Elmaksoud, S., Spencer, S. K., Gerba, C. P., Tamimi, A. H., Jokela, W. E., & Borchardt, M. A. (2014). Simultaneous Concentration of Bovine Viruses and Agricultural Zoonotic Bacteria from Water Using Sodocalcic Glass Wool Filters. Food and environmental virology.
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  Infiltration and runoff from manured agricultural fields can result in livestock pathogens reaching groundwater and surface waters. Here, we measured the effectiveness of glass wool filters to simultaneously concentrate enteric viruses and bacteria of bovine origin from water. The recovery efficiencies were determined for bovine viral diarrhea virus types 1 and 2, bovine rotavirus group A, bovine coronavirus, poliovirus Sabin III, toxigenic Escherichia coli ,and Campylobacter jejuni seeded into water with three different turbidity levels (0.5, 215, and 447 NTU). Twenty liters of dechlorinated tap water (pH 7) were seeded with the test organisms, and then passed through a glass wool filter using a peristaltic pump (flow rate = 1 liter min(-1)). Retained organisms were eluted from the filters by passing beef extract-glycine buffer (pH 9.5) in the direction opposite of sample flow. Recovered organisms were enumerated by qPCR except for C. jejuni, which was quantified by culture. Mean recovery efficiencies ranged from 55 to 33 % for the bacteria and 58 to 16 % for the viruses. Using bootstrapping techniques combined with Analysis of Variance, recovery efficiencies were found to differ among the pathogen types tested at the two lowest turbidity levels; however, for a given pathogen type turbidity did not affect recovery except for C. jejuni. Glass wool filtration is a cost-effective method for concentrating several waterborne pathogens of bovine origin simultaneously, although recovery may be low for some specific taxa such as bovine viral diarrhea virus 1.
• Beamer, P. I., Plotkin, K. R., Gerba, C. P., Sifuentes, L. Y., Koenig, D. W., & Reynolds, K. A. (2014). Modeling of Human Viruses on Hands and Risk of Infection in an Office Workplace Using Micro-Activity Data. Journal of occupational and environmental hygiene, 0.
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  ABSTRACT Although the number of illnesses resulting from indirect viral pathogen transmission could be substantial, it is difficult to estimate the relative risks because of the wide variation and uncertainty in human behavior, variable viral concentrations on fomites, and other exposure factors. The purpose of this study was to evaluate the micro-activity approach for assessment of microbial risk by adapting a mathematical model to estimate probability of viral infection from indirect transmission. To evaluate the model, measurements of phage loading on fomites and hands collected before and after implementation of a Healthy Workplace Project(TM) intervention were used. Parameter distributions were developed from this data, as well as for micro-activity rates, contact surface areas, phage transfer efficiencies, and inactivation rates. Following the Monte Carlo simulations (n = 1,000), the estimated phage loading on hands was not significantly different from the loading of phage on hands measured in the experimental trials. The model was then used to demonstrate that the Healthy Workplace Project(TM) intervention significantly reduced risk of infection by 77% for rotavirus and rhinovirus. This is the first published study to successfully evaluate a model focused on the indirect transmission of viruses via hand contact with measured data and provide an assessment of the micro-activity approach to microbial risk evaluation.
• Betancourt, W. Q., Kitajima, M., Wing, A. D., Regnery, J., Drewes, J. E., Pepper, I. L., & Gerba, C. P. (2014). Assessment of virus removal by managed aquifer recharge at three full-scale operations. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 49(14), 1685-92.
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  Managed aquifer recharge (MAR) systems such as riverbank filtration and soil-aquifer treatment all involve the use of natural subsurface systems to improve the quality of recharged water (i.e. surface water, stormwater, reclaimed water) before reuse. During MAR, water is either infiltrated via basins, subsurface injected or abstracted from wells adjacent to rivers. The goal of this study was to assess the removal of selected enteric viruses and a potential surrogate for virus removal at three full-scale MAR systems located in different regions of the United States (Arizona, Colorado, and California). Samples of source water (i.e., river water receiving treated wastewater and reclaimed water) before recharge and recovered groundwater at all three sites were tested for adenoviruses, enteroviruses, Aichi viruses and pepper mild mottle virus (PMMoV) by quantitative polymerase chain reaction (qPCR). Samples of groundwater positive for any virus were also tested for the presence of infectious virus by cell culture. PMMoV was the most commonly detected virus in the groundwater samples. Infectious enteric viruses (reovirus) were only detected in one groundwater sample with a subsurface residence time of 5 days. The results suggested that in groundwater with a residence time of greater than 14 days all of the viruses are removed below detection indicating a 1 to greater than 5 log removal depending upon the type of virus. Given its behavior, PMMoV may be suitable to serve as a conservative tracer of enteric virus removal in managed aquifer treatment systems.
• Chaidez, C., Soto-Beltran, M., Gerba, C. P., & Tamimi, A. H. (2014). Reduction of risk of Salmonella infection from kitchen cleaning clothes by use of sodium hypochlorite disinfectant cleaner. Letters in applied microbiology, 59(5), 487-92.
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  The objective of this study was to evaluate the reduction of infection risk due to exposure to Salmonella sp. in kitchen cleaning clothes by the use of a bleach (sodium hypochlorite) cleaner utilizing a continuous-time dynamic exposure model. The only route of exposure considered was hand contamination during cloth use. The occurrence and numbers of Salmonella was studied in 60 homes over a 6-week period in which half disinfected kitchen cleaning clothes with a sodium hypochlorite based disinfectant cleaner. This study demonstrated that a significant risk exists for Salmonella infection from kitchen cleaning clothes in Mexican homes and that this risk can be reduced by almost 100-fold by soaking cleaning clothes in a bleach product. The risks of infection and illness could likely be further reduced by developing a more effective procedure for reducing Salmonella in cleaning clothes treated twice a day with a sodium hypochlorite disinfectant (i.e. longer soaking time) or using a greater concentration of the disinfectant.
• Fankem, S. L., Boone, S. A., Gaither, M., & Gerba, C. P. (2014). Outbreak of norovirus illness in a college summer camp: impact of cleaning on occurrence of norovirus on fomites. Journal of environmental health, 76(8), 20-6.
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  During the summer of 2005 an outbreak of norovirus acute gastroenteritis occurred in a residential college summer camp and was reported to the local health department. The outbreak spread rapidly to several other groups concurrently sharing the same facilities. During the investigation, fomites were sampled at different times in dorm rooms and tested for norovirus. The number of norovirus-positive rooms increased after the first room cleaning, from 40% to 73%. After the initial cleaning, the staff was instructed on proper cleaning and disinfection procedures and provided with disposable disinfecting wipes to reduce cross contamination, and the number of norovirus-positive rooms decreased to 30%. These findings reinforce the need for appropriate cleaning and disinfection procedures during a norovirus outbreak.
• Gerba, C. P., Abd-Elmaksoud, S., Newick, H., El-Esnawy, N. A., Barakat, A., & Ghanem, H. (2014). Assessment of Coliphage Surrogates for Testing Drinking Water Treatment Devices. Food and environmental virology.
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  Test protocols have been developed by the United States Environmental Protection Agency (USEPA) and the World Health Organization (WHO) to test water treatment devices/systems that are used at the individual and home levels to ensure the removal of waterborne viruses. The goal of this study was to assess if coliphage surrogates could be used in this testing in place of the currently required use of animal or human enteric viruses. Five different coliphages (MS-2, PRD1, ΦX-174, Qβ, and fr) were compared to the removal of poliovirus type 1 (LSc-2ab) by eight different water treatment devices/systems using a general case and a challenge case (high organic load, dissolved solids, and turbidity) test water as defined by the USEPA. The performance of the units was rated as a pass/fail based on a 4 log removal/inactivation of the viruses. In all cases, a failure or a pass of the units/system for poliovirus also corresponded to a pass/fail by all of the coliphages. In summary, in using pass/fail criteria as recommended under USEPA guidelines for testing water treatment device/systems, the use of coliphages should be considered as an alternative to reduce cost and time of testing such devices/systems.
• Gerba, C. P., Tamimi, A., Sifuentes, L., Hoffman, D., & Koenig, D. (2014). Bacterial occurrence in kitchen hand towels. Food Protection Trends, 34, 312-317.
• Kitajima, M., Haramoto, E., Iker, B. C., & Gerba, C. P. (2014). Occurrence of Cryptosporidium, Giardia, and Cyclospora in influent and effluent water at wastewater treatment plants in Arizona. Science of the Total Environment, 484(1), 129-136.
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  Abstract: We investigated the occurrence of Cryptosporidium, Giardia, and Cyclospora at two wastewater treatment plants (WWTPs) in Arizona over a 12-month period, from August 2011 to July 2012. Influent and effluent wastewater samples were collected monthly, and protozoan (oo)cysts were concentrated using an electronegative filter, followed by the detection of protozoa using fluorescent microscopy (Cryptosporidium oocysts and Giardia cysts) and PCR-based methods (Cryptosporidium spp., Giardia intestinalis, and Cyclospora cayetanensis). The concentration of Giardia cysts in the influent was always higher than that of Cryptosporidium oocysts (mean concentration of 4.8-6.4×103 versus 7.4×101-1.0×102(oo)cysts/l) with no clear seasonality, and log10 reduction of Giardia cysts was significantly higher than that of Cryptosporidium oocysts for both WWTPs (P
• Kitajima, M., Haramoto, E., Iker, B. C., & Gerba, C. P. (2014). Occurrence of Cryptosporidium, Giardia, and Cyclospora in influent and effluent water at wastewater treatment plants in Arizona. The Science of the total environment, 484, 129-36.
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  We investigated the occurrence of Cryptosporidium, Giardia, and Cyclospora at two wastewater treatment plants (WWTPs) in Arizona over a 12-month period, from August 2011 to July 2012. Influent and effluent wastewater samples were collected monthly, and protozoan (oo)cysts were concentrated using an electronegative filter, followed by the detection of protozoa using fluorescent microscopy (Cryptosporidium oocysts and Giardia cysts) and PCR-based methods (Cryptosporidium spp., Giardia intestinalis, and Cyclospora cayetanensis). The concentration of Giardia cysts in the influent was always higher than that of Cryptosporidium oocysts (mean concentration of 4.8-6.4×10(3) versus 7.4×10(1)-1.0×10(2)(oo)cysts/l) with no clear seasonality, and log10 reduction of Giardia cysts was significantly higher than that of Cryptosporidium oocysts for both WWTPs (P
• Kitajima, M., Iker, B. C., Pepper, I. L., & Gerba, C. P. (2014). Relative abundance and treatment reduction of viruses during wastewater treatment processes--identification of potential viral indicators. The Science of the total environment, 488-489, 290-6.
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  Waterborne pathogenic viruses discharged from wastewater treatment plants (WWTPs) pose potential public health risks. In the present study, we investigated the relative abundance, occurrence, and reduction of eleven different viruses at two WWTPs in southern Arizona over a 12-month period, from August 2011 to July 2012. Influent and effluent samples from the two WWTPs were collected monthly. Viruses were concentrated using an electronegative filter method and quantified using TaqMan-based quantitative PCR (qPCR) assays for each of the virus types (i.e., genogroup I, II and IV noroviruses, sapovirus, enterovirus, group A rotavirus, Aichi virus, pepper mild mottle virus, adenovirus, and JC and BK polyomaviruses), with murine norovirus internal control for the monitoring of extraction-RT-qPCR efficiencies. The pepper mild mottle virus, a plant virus, was found to be the most prevalent virus in both influent and effluent wastewater (annual mean concentration of 3.7-4.4×10(6) copies/L and 4.6-6.3×10(5) copies/L in influent and effluent wastewater, respectively), showing a low reduction by the treatment processes (0.76-0.99 annual mean log10 reduction), and no significant seasonal change in concentration. Aichi virus, a human enteric virus, was also found in greater abundance, and showed lower reduction during wastewater treatment than other human enteric viruses. Our results suggest that these viruses could be used as potential indicators of wastewater reclamation system performance, with respect to virus occurrence and removal.
• Kitajima, M., Iker, B. C., Rachmadi, A. T., Haramoto, E., & Gerba, C. P. (2014). Quantification and genetic analysis of salivirus/klassevirus in wastewater in Arizona, USA. Food and environmental virology, 6(3), 213-6.
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  Salivirus/klassevirus sequences were identified in 7 (15%) wastewater samples collected in Arizona monthly for a year, with the highest concentration of 2.28 × 10(5) and 2.46 × 10(4) copies/L in influent and effluent, respectively. This is the first report of quantification and genetic analysis of salivirus/klassevirus in water samples in the United States.
• Lopez, G. U., Kitajima, M., Havas, A., Gerba, C. P., & Reynolds, K. A. (2014). Evaluation of a disinfectant wipe intervention on fomite-to-finger microbial transfer. Applied and environmental microbiology, 80(10), 3113-8.
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  Inanimate surfaces, or fomites, can serve as routes of transmission of enteric and respiratory pathogens. No previous studies have evaluated the impact of surface disinfection on the level of pathogen transfer from fomites to fingers. Thus, the present study investigated the change in microbial transfer from contaminated fomites to fingers following disinfecting wipe use. Escherichia coli (10(8) to 10(9) CFU/ml), Staphylococcus aureus (10(9) CFU/ml), Bacillus thuringiensis spores (10(7) to 10(8) CFU/ml), and poliovirus 1 (10(8) PFU/ml) were seeded on ceramic tile, laminate, and granite in 10-μl drops and allowed to dry for 30 min at a relative humidity of 15 to 32%. The seeded fomites were treated with a disinfectant wipe and allowed to dry for an additional 10 min. Fomite-to-finger transfer trials were conducted to measure concentrations of transferred microorganisms on the fingers after the disinfectant wipe intervention. The mean log10 reduction of the test microorganisms on fomites by the disinfectant wipe treatment varied from 1.9 to 5.0, depending on the microorganism and the fomite. Microbial transfer from disinfectant-wipe-treated fomites was lower (up to
• Lopez, G. U., Lopez, G. U., Kitajima, M., Kitajima, M., Havas, A., Havas, A., Gerba, C. P., Gerba, C. P., Reynolds, K. A., & Reynolds, K. A. (2014). Evaluation of a Disinfectant Wipe Intervention on Fomite-to-Finger Microbial Transfer. Applied Environmental Microbiology, 80(10), 3113-3118.
• Lopez, G. U., Lopez, G. U., Kitajima, M., Kitajima, M., Sexton, J. D., Sexton, J. D., Gerba, C. P., Gerba, C. P., Reynolds, K. A., & Reynolds, K. A. (2015). Risk of Campylobacter jejuni Infection from Preparing Raw Chicken in Domestic Kitchens and Reduction of Cross-contamination Using Disinfectant Wipes. Journal of Applied Microbiology, 119, 245-252.
• Martínez-Bastidas, T., Castro-Del Campo, N., Mena, K., Campo, N., León-Félix, J., Gerba, C., & Chaidez, C. (2014). Detection of Pathogenic Microorganisms on Children ́s Hands and Toys during Play. Journal of applied microbiology.
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  This study aimed to determine if the children ́s leisure activities impact the presence of pathogens on their hands and toys.
• Ryan, M. O., Haas, C. N., Gurian, P. L., Gerba, C. P., Panzl, B. M., & Rose, J. B. (2014). Application of quantitative microbial risk assessment for selection of microbial reduction targets for hard surface disinfectants. American journal of infection control, 42(11), 1165-72.
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  This quantitative microbial risk assessment (QMRA) included problem formulation for fomites and hazard identification for 7 microorganisms, including pathogenic Escherichia coli and E coli 0157:H7, Listeria monocytogenes, norovirus, Pseudomonas spp, Salmonella spp, and Staphylococcus aureus. The goal was to address a risk-based process for choosing the log10 reduction recommendations, in contrast to the current US Environmental Protection Agency requirements.
• Samendra, S., Masaaki, K., Gerba, C. P., & Pepper, I. L. (2014). Rapid detection technologies for monitoring microorganisms in water. Biosenors Journal, 34(1), doi10.4172/2090-4967.1000109.
• Sherchan, S. P., Snyder, S. A., Gerba, C. P., & Pepper, I. L. (2014). Inactivation of MS2 coliphage by UV and hydrogen peroxide: comparison by cultural and molecular methodologies. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 49(4).
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  The use of advanced oxidation processes (AOP) are expected to increase for removal of emerging contaminants and pathogens from drinking water. In this study, the performance of a small community ultraviolet light reactor in combination with hydrogen peroxide (H2O2) for MS2 coliphage inactivation with two different flow rate conditions of 1 gal/min (gpm) and 2 gpm was evaluated. Following UV radiation, MS2 showed a reduction of 5.3-5.8 log10 when quantified with cultural plaque counts, whereas corresponding quantitative polymerase chain reaction (qPCR) data showed only a 1.7-2.8 log10 reduction in viral RNA copy number. When H2O2 was added at either 2.5 or 5 ppm with UV at both flow rate conditions, enhanced MS2 inactivation occurred with a more than 7 log10 reduction observed via plaque counts, indicating that all added MS2 had been inactivated, since no plaques were formed after incubation at 37 °C for 24 h. In contrast, qPCR only showed a corresponding 3-4 log10 reduction in viral RNA copy number. This research also sheds light on the inactivation of MS2 with ultraviolet light and in the presence of hydroxyl radicals and provides a practical use of qPCR to detect MS2 concentration following advanced oxidation relative to traditional plaque methodology; however qPCR detection overestimates the true number of infective virus.
• Sherchan, S. P., Snyder, S. A., Gerba, C. P., & Pepper, I. L. (2014). Online monitoring of Escherichia coli and Bacillus thuringiensis spore inactivation after advanced oxidation treatment. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 49(8), 933-9.
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  Various studies have shown that advanced oxidation processes (AOPs) such as UV light in combination with hydrogen peroxide is an efficient process for the removal of a large variety of emerging contaminants including microorganisms. The mechanism of destruction in the presence of hydrogen peroxide (H2O2) is the enhanced formation of hydroxyl (·OH) radicals, which have a high oxidation potential. The goal of this study was to utilize in-line advanced oxidation to inactivate microbes, and document the inactivation via an in-line, real-time sensor. Escherichia coli cells and Bacillus thuringiensis spores were exposed to UV/H2O2 treatment in DI water, and the online sensor BioSentry(®) was evaluated for its potential to monitor inactivation in real-time. B. thuringiensis was selected as a non-pathogenic surrogate for B. anthracis, the causative agent of anthrax and a proven biological weapon. UV radiation and UV/H2O2 exposure resulted in a >6 log10 reduction of the viable culturable counts of E. coli vegetative cells, and a 3 log10 reduction of B. thuringiensis spores. Scanning electron microscopy of the treated samples revealed severe damage on the surface of most E. coli cells, yet there was no significant change observed in the morphology of the B. thuringiensis spores. Following AOP exposure, the BioSentry sensor showed an increase in the categories of unknown, rod and spores counts, but overall, did not correspond well with viable count assays. Data from this study show that advanced oxidation processes effectively inactivate E. coli vegetative cells, but not B. thuringiensis spores, which were more resistant to AOP. Further, the BioSentry in-line sensor was not successful in documenting destruction of the microbial cells in real-time.
• Sifuentes, L. Y., Choate, B. L., Gerba, C. P., & Bright, K. R. (2014). The occurrence of Naegleria fowleri in recreational waters in Arizona. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 49(11), 1322-30.
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  Naegleria fowleri is a free-living amoeba found in waters in warmer regions that causes primary amoebic meningoencephalitis, a rare but almost universally fatal disease. The goal of this project was to assess the occurrence of N. fowleri and other thermophilic amoebae in 33 recreational surface waters across Arizona to determine if their presence could be correlated with seasonal or other environmental factors. First, 1-L grab samples were collected over two years and analyzed using polymerase chain reaction and amoebae viability. Seasonality was observed, with N. fowleri and thermophilic amoebae (20% and 30%, respectively) being detected more often in the winter and spring combined than in the summer and fall combined (7.9% and 9.5%, respectively). The spring and fall both had an average temperature of 18°C, yet had different occurrence data (18.2% versus 5.9% for N. fowleri, respectively; 27.3% versus 0% for viable amoebae, respectively). These results are in stark contrast to previous studies in which N. fowleri has been found almost exclusively during warmer months. Over the two-year study, N. fowleri was detected in six and thermophilic amoebae in eight of the 33 recreational water bodies. Five of these were lakes near Phoenix that tested positive for N. fowleri and thermophilic amoebae over multiple seasons. These lakes differed significantly (P ≤ 0.05) from the other 28 surface waters, with a lower average temperature in the spring, a higher temperature in the fall, a higher pH and turbidity in the summer, and a lower electro-conductivity in the spring. They also had lower Escherichia coli and heterotrophic bacteria levels during colder months. Future N. fowleri monitoring in Arizona should focus on these five lakes to further elucidate the factors that contribute to the low occurrence of this amoeba in the summer or which might explain why these lakes appear to be reservoirs for the organism.
• Sifuentes, L. Y., Koenig, D. W., Phillips, R. L., Reynolds, K. A., & Gerba, C. P. (2014). Use of hygiene protocols to control the spread of viruses in a hotel. Food and environmental virology, 6(3), 175-81.
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  The goals of this study were to observe the spread of viruses in a hotel setting and to assess the effectiveness of a hygiene intervention in reducing their spread. Selected fomites in one hotel room were inoculated with bacteriophage ϕx-174, and fomites in a conference center within the same hotel were inoculated using bacteriophage MS2. Cleaning of the contaminated room resulted in the spread of viruses to other rooms by the housekeeping staff. Furthermore, viruses were transferred by hotel guests to the conference center and a communal kitchen area. Additionally, conference attendees transferred viruses from the conference center to their hotel rooms and a communal kitchen area. This study demonstrated how viruses can be spread throughout a hotel setting by both housekeepers and guests. A hygiene intervention, which included providing hand hygiene products and facial tissues to the guests and disinfecting solutions with disposable wipes to the housekeeping staff, was successful in reducing the spread of viruses between the hotel guest rooms and conference center. The hygiene intervention resulted in significantly reduced transfer of the ϕx-174 between the contaminated hotel room and other hotel rooms, communal areas, and the conference center (p = 0.02).
• Song, I., O’Shaughnessy, A., Gerba, C. P., & Choi, C. Y. (2014). . Impacts of tilling and covering treatments on the biosolids solar drying conversions from Class B to Class A. Environmental Technology, 35, 2610-2618.
• Soto Beltran, M., Gerba, C. P., Porto Fett, A., Luchansky, J. B., & Chaidez, C. (2014). Prevalence and characterization of Listeria monocytogenes, Salmonella and Shiga toxin-producing Escherichia coli isolated from small Mexican retail markets of queso fresco. International journal of environmental health research, 1-9.
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  Queso fresco (QF) is a handmade cheese consumed and produced in Latin America. In Mexico, QF production is associated with a microbiological risk. The aim of the study was to determine the incidence and characterization of Listeria monocytogenes, Salmonella spp., and Shiga toxin-producing Escherichia coli (STEC) in QF from retail markets of the north-western State of Sinaloa, Mexico, and to assess the effect of physicochemical parameters on Listeria presence. A total of 75 QF samples were obtained. L. monocytogenes, E. coli, and coliforms were detected in 9.3, 94, and 100 %, respectively. Salmonella was not detected. STEC isolates showed virulence genes. Microbial loads were above the maximum values recommended by the Official Mexican Standards. Physicochemical parameters such as water activity (aw), moisture content, pH, and salinity played a role in Listeria prevalence in QF. Rigorous control in QF made in Culiacan, Mexico is needed to reduce the risk of foodborne pathogens.
• Suppes, L. M., Abrell, L. M., A, D. P., Gerba, C. P., Reynolds, K. A., Suppes, L. M., Abrell, L. M., A, D. P., Gerba, C. P., & Reynolds, K. A. (2014). Assessment of Swimmer Head Submersion Exposures and Pool Water Ingestion.. Journal of Water and Health, 12(2), 269-279.
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  ABSTRACTEnteric pathogens in pool water can be unintentionally ingested during swimming, increasing the likelihood of acute gastrointestinal illness (AGI). AGI cases in outbreaks are more likely to submerge heads than non-cases, but an association is unknown since outbreak data are self-reported and prone to bias. In the present study, head submersion frequency and duration were observed and analyzed for associations with pool water ingestion measured using ultra high pressure liquid chromatography – tandem mass spectrometry. Frequency of splashes to the face was also quantified. Reliable tools that assess activities associated with pool water ingestion are needed to identify ingestion risk factors and at-risk populations. Objectives were to determine if the observed activities were associated with ingestion, and to test environmental sensor and videography assessment tools. Greater frequency and duration of head submersion were not associated with ingestion, but frequency of splashes to the face, leisurely swimming, and being ≤18 were. Videography was validated for assessing swimmer head submersion frequency. Results demonstrate ingestion risk factors can be identified using videography and urine analysis techniques. Expanding surveys to include questions on leisure swimming participation and frequency of splashes to the face is recommended to improve exposure assessment during outbreak investigations.Keywords: exposure factor; head submersion; ingestion; pool; recreational water; swimming
• Tamimi, A. H., Carlino, S., & Gerba, C. P. (2014). Long-term efficacy of a self-disinfecting coating in an intensive care unit. American journal of infection control, 42(11), 1178-81.
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  Cleaning and disinfecting fomites can effectively remove/kill pathogens on surfaces, but studies have shown that more than one-half the time, surfaces are not adequately cleaned or are recontaminated within minutes. This study evaluated a product designed to create a long-lasting surface coating that provides continuous disinfecting action.
• Tamimi, A. H., Carlino, S., Edmonds, S., & Gerba, C. P. (2014). Impact of an alcohol-based hand sanitizer intervention on the spread of viruses in homes. Food and environmental virology, 6(2), 140-4.
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  The objectives of this study were to determine the movement of a virus throughout a household and the impact of an alcohol-based hand sanitizer (ABHS) on reducing the movement and exposure of the virus to household members. Bacterial virus MS-2 was used as the surrogate for human enteric and respiratory viruses. Seven households with families having at least two children in the age range of 2-18 living in the home were used in this study. The hands of one adult family member were contaminated with 1 × 10(8). MS-2 bacteriophage in each home. After 8 h, the hands of each family member (10 fingers) and 20 frequently touched fomites were sampled to determine baseline contamination without intervention. Within 8 h, MS-2 was detected on all of the family member's hands and most of the fomites. The intervention consisted of providing the families in all selected homes with bottles of an ABHS, which were placed in the kitchen, bathrooms, and nurseries. Smaller individual bottles were provided for each family member greater than 12 years old to place in purses, pockets, backpacks, etc. The families were instructed to use the ABHS one time or three times during the day. For one and three uses, a statistically significant reduction of virus on un-inoculated and inoculated hands of ~99% occurred within 8 h. Similar reductions occurred on fomites throughout the households (97-99%). These results demonstrate that the use of an ABHS can significantly reduce transfer of a virus to the hands, and to the commonly touched surfaces within the household.
• Abd-Elmaksoud, S., Naranjo, J. E., & Gerba, C. P. (2013). Assessment of a Portable Handheld UV Light Device for the Disinfection of Viruses and Bacteria in Water. Food and Environmental Virology, 5(2), 87-90.
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  PMID: 23412725;Abstract: Effective individual microbiological water purifiers are needed for consumption of untreated water sources by campers, emergency use, military, and in developing counties. A handheld UV light device was tested to assess if it could meet the virus reduction requirements established by the United State Environmental Protection Agency, National Science Foundation and the World Health Organization. The device was found capable of inactivating at least 4 log10 of poliovirus type 1, rotavirus SA-11 and MS-2 virus in 500 mL volumes of general case test water. But in the presence of high turbidity and organic matter, filtration was necessary to achieve a 4 log10 reduction of the test viruses. © 2013 Springer Science+Business Media New York.
• Artiola, J. F., Hix, G., Gerba, C. P., Farrell-Poe, K. L., Artiola, J. F., Hix, G., Gerba, C. P., & Farrell-Poe, K. L. (2013). What Well Owners Should Know about Shock Chlorination. UA CALS Cooperative Extension, AZ1605.
• Engelbrecht, K., Ambrose, D., Sifuentes, L., Gerba, C., Weart, I., & Koenig, D. (2013). Decreased activity of commercially available disinfectants containing quaternary ammonium compounds when exposed to cotton towels. American Journal of Infection Control, 41(10), 908-911.
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  PMID: 23623007;Abstract: Background: Health care-associated infections (HAIs) are a significant problem in hospitals, and environmental surfaces have been implicated as a source of HAIs in the hospital environment. Furthermore, Gram-negative and Gram-positive bacteria can persist on dry environmental surfaces for as long as several months. Poorly cleaned surfaces may serve as vehicles for microbes, which may then be transferred to patients. Methods: Cotton and microfiber towels were both tested for their abilities to bind quaternary ammonium compounds (QACs). The towels were exposed to 3 commercially available disinfectants for 0.5, 30, and 180 minutes. Germicidal spray tests (GSTs) were performed for all towel eluates in accordance with the AOAC International method 961.02. Cotton towel eluates were analyzed for QAC concentration using high-performance liquid chromatography. Results: QAC concentrations were reduced by up to 85.3% after exposure to cotton towels, resulting in failure of the disinfectants exposed to cotton towels in 96% of the GSTs. Conclusion: The use of cotton towels with QAC-based cleansers should be reconsidered, particularly in hospitals where effective cleaning of the patient environment is needed to reduce the risk of HAIs. Copyright © 2013 by the Association for Professionals in Infection Control and Epidemiology, Inc.
• Engelbrecht, K., Ambrose, D., Sifuentes, L., Gerba, C., Weart, I., & Koenig, D. (2013). Decreased activity of commercially available disinfectants containing quaternary ammonium compounds when exposed to cotton towels. American journal of infection control, 41(10).
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  Health care-associated infections (HAIs) are a significant problem in hospitals, and environmental surfaces have been implicated as a source of HAIs in the hospital environment. Furthermore, Gram-negative and Gram-positive bacteria can persist on dry environmental surfaces for as long as several months. Poorly cleaned surfaces may serve as vehicles for microbes, which may then be transferred to patients.
• Gerba, C. P. (2013). Evaluation of real-time water quality sensors for the detection of intentional bacterial spore contamination of portable water. Biosensors and Bioelectronics, 4:141.doi:10.4172/2155-6210.1000141(4), 4.
• Gerba, C. P., Maxwell, S., Sifuentes, L. Y., & Tamimi, A. H. (2013). Impact of a disinfecting wipe on bacterial contamination in households. Household and Personal Care, 8(3), 24-26.
• Gerba, C. P., Soto-Beltran, M., Mena, K. D., Tarwater, P. M., Reynolds, K., & Chaidez, C. (2013). . Risk assessment of Listeria monocytogenes in queso fresco in Culiacan, Mexico. J. Microbiol. Res, 3(3), 111-116.
• Kim, M., Choi, C. Y., & Gerba, C. P. (2013). Development and evaluation of a decision-supporting model for identifying the source location of microbial intrusions in real gravity sewer systems. Water Research, 47(13), 4630-4638.
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  PMID: 23770478;Abstract: Assuming a scenario of a hypothetical pathogenic outbreak, we aimed this study at developing a decision-support model for identifying the location of the pathogenic intrusion as a means of facilitating rapid detection and efficient containment. The developed model was applied to a real sewer system (the Campbell wash basin in Tucson, AZ) in order to validate its feasibility. The basin under investigation was divided into 14 sub-basins. The geometric information associated with the sewer network was digitized using GIS (Geological Information System) and imported into an urban sewer network simulation model to generate microbial breakthrough curves at the outlet. A pre-defined amount of Escherichia coli (E. coli), which is an indicator of fecal coliform bacteria, was hypothetically introduced into 56 manholes (four in each sub-basin, chosen at random), and a total of 56 breakthrough curves of E. coli were generated using the simulation model at the outlet. Transport patterns were classified depending upon the location of the injection site (manhole), various known characteristics (peak concentration and time, pipe length, travel time, etc.) extracted from each E. coli breakthrough curve and the layout of sewer network. Using this information, we back-predicted the injection location once an E. coli intrusion was detected at a monitoring site using Artificial Neural Networks (ANNs). The results showed that ANNs identified the location of the injection sites with 57% accuracy; ANNs correctly recognized eight out of fourteen expressions with relying on data from a single detection sensor. Increasing the available sensors within the basin significantly improved the accuracy of the simulation results (from 57% to 100%). © 2013 Elsevier Ltd.
• Kim, M., Choi, C. Y., & Gerba, C. P. (2013). Development and evaluation of a decision-supporting model for identifying the source location of microbial intrusions in real gravity sewer systems. Water research, 47(13).
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  Assuming a scenario of a hypothetical pathogenic outbreak, we aimed this study at developing a decision-support model for identifying the location of the pathogenic intrusion as a means of facilitating rapid detection and efficient containment. The developed model was applied to a real sewer system (the Campbell wash basin in Tucson, AZ) in order to validate its feasibility. The basin under investigation was divided into 14 sub-basins. The geometric information associated with the sewer network was digitized using GIS (Geological Information System) and imported into an urban sewer network simulation model to generate microbial breakthrough curves at the outlet. A pre-defined amount of Escherichia coli (E. coli), which is an indicator of fecal coliform bacteria, was hypothetically introduced into 56 manholes (four in each sub-basin, chosen at random), and a total of 56 breakthrough curves of E. coli were generated using the simulation model at the outlet. Transport patterns were classified depending upon the location of the injection site (manhole), various known characteristics (peak concentration and time, pipe length, travel time, etc.) extracted from each E. coli breakthrough curve and the layout of sewer network. Using this information, we back-predicted the injection location once an E. coli intrusion was detected at a monitoring site using Artificial Neural Networks (ANNs). The results showed that ANNs identified the location of the injection sites with 57% accuracy; ANNs correctly recognized eight out of fourteen expressions with relying on data from a single detection sensor. Increasing the available sensors within the basin significantly improved the accuracy of the simulation results (from 57% to 100%).
• Kitajima, M., Gerba, C. P., Pepper, I. L., Bright, K. R., & Iker, B. C. (2013). Evaluation of commercial kits for the extraction and purification of viral nucleic acids from environmental and fecal samples. JOURNAL OF VIROLOGICAL METHODS, 191(1), 24-30. doi:https://doi.org/10.1016/j.jviromet.2013.03.011
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  The extraction and purification of nucleic acids is a critical step in the molecular detection of enteric viruses from environmental or fecal samples. In the present study, the performance of three commercially available kits was assessed: the MO BIO PowerViral Environmental DNA/RNA Isolation kit, the Qiagen QIAamp Viral RNA Mini kit, and the Zymo ZR Virus DNA/RNA Extraction kit. Viral particles of adenovirus 2 (AdV), murine norovirus (MNV), and poliovirus type 1 (PV1) were spiked in molecular grade water and three different types of sample matrices (i.e., biosolids, feces, and surface water concentrates), extracted with the kits, and the yields of the nucleic acids were determined by quantitative PCR (qPCR). The MO BIO kit performed the best with the biosolids, which were considered to contain the highest level of inhibitors and provided the most consistent detection of spiked virus from all of the samples. A qPCR inhibition test using an internal control plasmid DNA and a nucleic acid purity test using an absorbance at 230 nm for the nucleic acid extracts demonstrated that the MO BIO kit was able to remove qPCR inhibitors more effectively than the Qiagen and Zymo kits. These results suggest that the MO BIO kit is appropriate for the extraction and purification of viral nucleic acids from environmental and clinical samples that contain high levels of inhibitors.
• Lopez, G. U., Gerba, C. P., Tamimi, A. H., Kitajima, M., Maxwell, S. L., & Rose, J. B. (2013). Transfer efficiency of bacteria and viruses from porous and nonporous fomites to fingers under different relative humidity conditions. Applied and Environmental Microbiology, 79(18), 5728-5734.
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  PMID: 23851098;PMCID: PMC3754157;Abstract: Fomites can serve as routes of transmission for both enteric and respiratory pathogens. The present study examined the effect of low and high relative humidity on fomite-to-finger transfer efficiency of five model organisms from several common inanimate surfaces (fomites). Nine fomites representing porous and nonporous surfaces of different compositions were studied. Escherichia coli, Staphylococcus aureus, Bacillus thuringiensis, MS2 coliphage, and poliovirus 1 were placed on fomites in 10-μl drops and allowed to dry for 30 min under low (15% to 32%) or high (40% to 65%) relative humidity. Fomite-to-finger transfers were performed using 1.0 kg/cm2 of pressure for 10 s. Transfer efficiencies were greater under high relative humidity for both porous and nonporous surfaces. Most organisms on average had greater transfer efficiencies under high relative humidity than under low relative humidity. Nonporous surfaces had a greater transfer efficiency (up to 57%) than porous surfaces (
• Lopez, G. U., Gerba, C. P., Tamimi, A. H., Kitajima, M., Maxwell, S. L., & Rose, J. B. (2013). Transfer efficiency of bacteria and viruses from porous and nonporous fomites to fingers under different relative humidity conditions. Applied and environmental microbiology, 79(18).
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  Fomites can serve as routes of transmission for both enteric and respiratory pathogens. The present study examined the effect of low and high relative humidity on fomite-to-finger transfer efficiency of five model organisms from several common inanimate surfaces (fomites). Nine fomites representing porous and nonporous surfaces of different compositions were studied. Escherichia coli, Staphylococcus aureus, Bacillus thuringiensis, MS2 coliphage, and poliovirus 1 were placed on fomites in 10-μl drops and allowed to dry for 30 min under low (15% to 32%) or high (40% to 65%) relative humidity. Fomite-to-finger transfers were performed using 1.0 kg/cm(2) of pressure for 10 s. Transfer efficiencies were greater under high relative humidity for both porous and nonporous surfaces. Most organisms on average had greater transfer efficiencies under high relative humidity than under low relative humidity. Nonporous surfaces had a greater transfer efficiency (up to 57%) than porous surfaces (
• Manshadi, F. D., Karpiscak, M., & Gerba, C. P. (2013). Enteric bacterial contamination and survival on produce during irrigation with dairy wastewater in the field. J. Water Reuse Desalination, 3(2), 102-116.
• Manshadi, F. D., Karpiscak, M., & Gerba, C. P. (2013). Enteric bacterial contamination and survival on produce during irrigation with dairy wastewater in the field. Journal of Water Reuse and Desalination, 3(2), 102-110.
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  Abstract: The goals of this study were to quantify enteric bacterial contamination and survival on several different types of produce during irrigation with wastewater from a dairy operation. Dairy wastewater was used to irrigate three different types of vegetable crops: lettuce, carrot, and bell pepper. This study was conducted over two consecutive growing seasons. Irrigation water and vegetable samples were examined for Escherichia coli and Clostridium perfringens. In the dairy wastewater, E. coli and C. perfringens concentrations averaged 8.2× 107 MPN/100 mL and 5.0× 104 CFU per 100 mL, respectively. Analysis of variance test results indicated that E. coli and C. perfringens concentrations detected on the three crops after irrigation were statistically different (p < 0.0001). The greatest contamination occurred on the carrots followed by lettuce and bell peppers. E. coli and C. perfringens were recovered from the carrots, bell peppers, and soil 49 days after wastewater irrigation of the plots had ceased. Moisture content of the soil was statistically significantly related to survival of the organisms in the soil. © IWA Publishing 2013.
• Miles, S. L., Sun, W., Gerba, C. P., & Pepper, I. L. (2013). . Survival of infectious prions during anaerobic digestion of municipal sewage sludge and lime stabilization. J. Residual Sci. Technol, 10, 69-75.
• Olyuorni, A., McLain, J. E., Bright, K., Gerba, C. P., & Pepper, I. L. (2013). . Influence of residence time of reclaimed water within distribution systems on water quality.. Journal of Water Reuse and Desalination, 3, 185-196.
• Pepper, I. L., Gerba, C. P., Mclain, J. E., Bright, K. R., Rock, C. M., & Ajibode, O. M. (2013). Influence of residence time of reclaimed water within distribution systems on water quality. JOURNAL OF WATER REUSE AND DESALINATION, 3(3), 185-196. doi:https:/doi.org/10.2166/wrd.2013.088
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  The influence of residence time of reclaimed water within water distribution systems on microbial water quality was evaluated in two wastewater reclamation facilities in southern Arizona over a 15-month period. These utilities differed in age, geographic location, means of treatment, and disinfection (i.e. UV versus chlorine). At both facilities, samples were collected from the point of compliance (POC) directly after disinfection, and at discrete locations with increasing distance from the POC. Following entry into reclaimed water distribution systems, overall microbial water quality decreased rapidly due to microbial regrowth. However, following such regrowth, microbial concentrations remained relatively constant. Water-based opportunistic pathogens (Legionella, Mycobacterium, and Aeromonas) were frequently detected in both reclaimed water systems. In contrast, waterborne indicators such as Escherichia coli and Enterococcus were rarely detected, and only at low concentrations. These dates suggest the need for new indicators of water-based pathogens to be developed. Rechlorination in one of the distribution systems only reduced the concentration of bacteria temporarily due to rapid dissipation of chlorine, and subsequent regrowth of both water-based pathogens and indicators. Amoebic activity was detected in approximately one-third of all samples tested from both utilities, but was not correlated with either water-based pathogens or indicators.
• Sifuentes, L. Y., Gerba, C. P., Weart, I., Engelbrecht, K., & Koenig, D. W. (2013). Microbial contamination of hospital reusable cleaning towels. American Journal of Infection Control, 41(10), 912-915.
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  PMID: 23523522;Abstract: Background: Hospital cleaning practices are critical to the prevention of nosocomial infection transmission. To this end, cloth towels soaked in disinfectants are commonly used to clean and disinfect hospital surfaces. Cloth cleaning towels have been linked to an outbreak of Bacillus cereus and have been shown to reduce the effectiveness of commonly used quaternary ammonium disinfectants. Thus, it is important to determine whether the reuse of cloth towels increases the risk of pathogen transmission in hospitals. Methods: The goal of this project was to determine the effects of laundry and cleaning practices commonly used in hospitals for washing, storage, and disinfection of cloth cleaning towels on their microbial loads. Results: Our results indicate that cloth towels used for cleaning hospital rooms contained high numbers of microbial contaminants. Conclusions: In this case, hospital laundering practices appear insufficient to remove microbial contaminants and may even add contaminants to the towels. Furthermore, it has been previously reported that towels can interfere with the action of common hospital disinfectants. Either independently or in combination, these 2 factors may increase the risk for transmission of pathogens in hospitals. These observations indicate the need to critically reevaluate current hospital cleaning practices associated with reuse of cloth towels. Copyright © 2013 by the Association for Professionals in Infection Control and Epidemiology, Inc.
• Sifuentes, L. Y., Gerba, C. P., Weart, I., Engelbrecht, K., & Koenig, D. W. (2013). Microbial contamination of hospital reusable cleaning towels. American journal of infection control, 41(10).
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  Hospital cleaning practices are critical to the prevention of nosocomial infection transmission. To this end, cloth towels soaked in disinfectants are commonly used to clean and disinfect hospital surfaces. Cloth cleaning towels have been linked to an outbreak of Bacillus cereus and have been shown to reduce the effectiveness of commonly used quaternary ammonium disinfectants. Thus, it is important to determine whether the reuse of cloth towels increases the risk of pathogen transmission in hospitals.
• Yépiz-Gómez, M. S., Gerba, C. P., & Bright, K. R. (2013). Survival of Respiratory Viruses on Fresh Produce. Food and environmental virology.
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  In addition to enteric viruses of fecal origin, emerging zoonotic viruses such as respiratory coronaviruses and influenza viruses may potentially be transmitted via contaminated foods. The goal of this study was to determine the recovery efficiencies and the survival of two respiratory viruses, namely, adenovirus 2 (Ad2) and coronavirus 229E (CoV229E), on fresh produce in comparison to the enteric poliovirus 1 (PV1). Adenovirus was recovered with efficiencies of 56.5, 31.8, and 34.8 % from lettuce, strawberries, and raspberries, respectively. Coronavirus was recovered from lettuce with an efficiency of 19.6 % yet could not be recovered from strawberries. Poliovirus was recovered with efficiencies of 76.7 % from lettuce, but only 0.06 % from strawberries. For comparison purposes, the survival of Ad2, CoV229E, and PV1 was determined for periods up to 10 days on produce. The enteric PV1 survived better than both respiratory viruses on lettuce and strawberries, with only ≤1.03 log10 reductions after 10 days of storage at 4 °C compared to CoV229E not being recovered after 4 days on lettuce and reductions of 1.97 log10 and 2.38 log10 of Ad2 on lettuce and strawberries, respectively, after 10 days. Nevertheless, these respiratory viruses were able to survive for at least several days on produce. There is therefore the potential for transfer to the hands and subsequently to the mucosa via rubbing the eyes or nose. In addition, some respiratory coronaviruses (e.g., severe acute respiratory syndrome coronavirus) and adenoviruses are also capable of replication in the gut and there is thus some potential for acquisition through the consumption of contaminated produce.
• Yépiz-Gómez, M., Gerba, C. P., & Bright, K. R. (2013). Survival of Respiratory Viruses on Fresh Produce. Food and Environmental Virology, 5(3), 150-156.
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  Abstract: In addition to enteric viruses of fecal origin, emerging zoonotic viruses such as respiratory coronaviruses and influenza viruses may potentially be transmitted via contaminated foods. The goal of this study was to determine the recovery efficiencies and the survival of two respiratory viruses, namely, adenovirus 2 (Ad2) and coronavirus 229E (CoV229E), on fresh produce in comparison to the enteric poliovirus 1 (PV1). Adenovirus was recovered with efficiencies of 56.5, 31.8, and 34.8 % from lettuce, strawberries, and raspberries, respectively. Coronavirus was recovered from lettuce with an efficiency of 19.6 % yet could not be recovered from strawberries. Poliovirus was recovered with efficiencies of 76.7 % from lettuce, but only 0.06 % from strawberries. For comparison purposes, the survival of Ad2, CoV229E, and PV1 was determined for periods up to 10 days on produce. The enteric PV1 survived better than both respiratory viruses on lettuce and strawberries, with only ≤1.03 log10 reductions after 10 days of storage at 4 °C compared to CoV229E not being recovered after 4 days on lettuce and reductions of 1.97 log10 and 2.38 log10 of Ad2 on lettuce and strawberries, respectively, after 10 days. Nevertheless, these respiratory viruses were able to survive for at least several days on produce. There is therefore the potential for transfer to the hands and subsequently to the mucosa via rubbing the eyes or nose. In addition, some respiratory coronaviruses (e.g., severe acute respiratory syndrome coronavirus) and adenoviruses are also capable of replication in the gut and there is thus some potential for acquisition through the consumption of contaminated produce. © 2013 Springer Science+Business Media New York.
• Ahmad, F., Pandey, A. K., Herzog, A. B., Rose, J. B., Gerba, C. P., & Hashsham, S. A. (2012). Environmental applications and potential health implications of quantum dots. Journal of Nanoparticle Research, 14(8).
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  Abstract: Quantum dots (QDs) are routinely employed for bioimaging applications and detection of pathogens and toxins. Their use as surrogates to study the fate and transport of non-fluorescent nanoparticles is limited due to high cost, detection of limit issues, and lack of sufficient data related to health effects. Systematic studies on the impact of QDs on environment and health may facilitate its safe use for environmental applications. This review summarizes the studies conducted with QDs with a focus on environmental applications and provides toxicity data important to human health. © 2012 Springer Science+Business Media B.V.
• Bright, K. R., Gerba, C. P., & Ikner, L. A. (2012). Concentration and recovery of viruses from water: a comprehensive review. FOOD AND ENVIRONMENTAL VIROLOGY, 4(2), 41-67. doi:https://doi.org/10.1007/s12560-012-9080-2
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  Enteric viruses are a cause of waterborne disease worldwide, and low numbers in drinking water can present a significant risk of infection. Because the numbers are often quite low, large volumes (100-1,000 L) of water are usually processed. The VIRADEL method using microporous filters is most commonly used today for this purpose. Negatively charged filters require the addition of multivalent salts and acidification of the water sample to effect virus adsorption, which can make large-volume sampling difficult. Positively charged filters require no preconditioning of samples, and are able to concentrate viruses from water over a greater pH range than electronegative filters. The most widely used electropositive filter is the Virosorb 1MDS; however, the Environmental Protection Agency has added the positively charged NanoCeram filters to their proposed Method 1615. Ultrafilters concentrate viruses based on size exclusion rather than electrokinetics, but are impractical for field sampling or processing of turbid water. Elution (recovery) of viruses from filters following concentration is performed with organic (e.g., beef extract) or inorganic solutions (e.g., sodium polyphosphates). Eluates are then reconcentrated to decrease the sample volume to enhance detection methods (e.g., cell culture infectivity assays and molecular detection techniques). While the majority of available filters have demonstrated high virus retention efficiencies, the methods to elute and reconcentrate viruses have met with varying degrees of success due to the biological variability of viruses present in water.
• Gerba, C. P., & Maxwell, S. (2012). Bacterial contamination of shopping carts and approaches to control. Food Protection Trends, 32(12), 747-749.
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  Abstract: Placing children in grocery shopping carts has been implicated recently as a source of infection with Salmonella and Campylobacter in young children. This study was conducted to assess the occurrence total bacteria, coliform bacteria and Escherichia coli on grocery shopping cart handles and seats. A total of 85 shopping carts in parking lots of grocery stores were tested in five major metropolitan areas across the United States. The total numbers of heterotrophic bacteria were as great as 1.1 × 107 on the handle and seat. Coliforms were detected on 72% (62) of the carts. E. coli was identified on 18 of 35 carts (51%) on which coliform identification was conducted. The results of this study suggest the need for improved sanitation of shopping cards/baskets to reduce exposure to pathogens and potential transmission of microbial infections among shoppers. Copyright© 2012, International Association for Food Protection.
• Gerba, C., Nordstrom, J. M., Reynolds, K. A., & Gerba, C. P. (2012). Comparison of bacteria on new, disposable, laundered, and unlaundered hospital scrubs. American journal of infection control, 40(6).
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  As a cost-saving measure, an increasing number of hospitals allow personnel to launder their uniforms, lab coats, and operating room scrubs at home. With rising nosocomial infection rates and increasing levels of multidrug-resistant bacteria in hospital settings, uniform contamination may be an environmental factor in the spread of infection.
• Gerba, C., Reynolds, K. A., Boone, S., Bright, K. R., & Gerba, C. P. (2012). Occurrence of household mold and efficacy of sodium hypochlorite disinfectant. Journal of occupational and environmental hygiene, 9(11).
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  The occurrence and distribution of mold on household surfaces and the efficacy of bleach-based (sodium hypochlorite, NaOCl) disinfectants on mold viability and allergenicity was documented. Household microenvironments prone to increased moisture were specifically targeted. Using the sticky tape method, 1330 samples were collected from non-porous indoor surfaces of 160 homes across the United States, and analyzed for mold. Homes were randomly selected and recruited via phone interviews. Culture and immunoassays were used to measure the viability and reduction of allergenic properties of Aspergillus fumigatus following 2.4% NaOCl treatment. All homes and 72.9% of surfaces tested positive for mold. Windowsills were the most frequently contaminated site (87.5%) and Cladosporium the most commonly identified mold (31.0%). Five-minute exposures to 2.4% NaOCl resulted in a >3 to >6-log₁₀ reduction of culturable mold counts in controlled laboratory studies. Organisms were nonculturable after 5- and 10-min contact times on non-porous and porous ceramic carriers, respectively, and A. fumigatus spore-eluted allergen levels were reduced by an average 95.8% in 30 sec, as indicated by immunoassay. All homes are contaminated with some level of mold, and regrowth is likely in moisture-prone microenvironments. The use of low concentrations (2.4%) of NaOCl for the reduction of culturable indoor mold and related allergens is effective and recommended.
• Gerba, C., Rodríguez, R. A., Gundy, P. M., Rijal, G. K., & Gerba, C. P. (2012). The impact of combined sewage overflows on the viral contamination of receiving waters. Food and environmental virology, 4(1).
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  The contribution of combined sewer overflows (CSO) to the viral contamination of receiving waters was determined. Adenovirus concentrations were determined using the Primary Liver Carcinoma (PLC/PRF/5) cell line and confirmed by Polymerase Chain Reaction (PCR). Norovirus concentration was determined using the Most Probable Number (MPN) and Reverse Transcription-Polymerase Chain Reaction (RT-PCR). Seventy-five water samples were collected during dry weather and 50 samples were collected during wet weather. CSO events significantly increased the concentration of culturable viruses, adenoviruses, and noroviruses in the receiving waters (P < 0.01). During dry weather, 56% of samples were positive for total virus cytopathic effects (CPE), adenoviruses were detected in 41% of the positive cell cultures, and noroviruses in 6% of the concentrates by direct RT-PCR. During wet weather, 100% of the samples were positive by CPE, 84% for adenoviruses, and 40% in the concentrates for norovirus. Our results demonstrate that CSOs can contribute significant viral loading to receiving waters.
• Herzog, A. B., Pandey, A. K., Reyes-Gastelum, D., Gerba, C. P., Rose, J. B., & Hashsham, S. A. (2012). Evaluation of sample recovery efficiency for bacteriophage P22 on fomites. Applied and Environmental Microbiology, 78(22), 7915-7922.
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  PMID: 22941090;PMCID: PMC3485962;Abstract: Fomites are known to play a role in the transmission of pathogens. Quantitative analysis of the parameters that affect sample recovery efficiency (SRE) at the limit of detection of viruses on fomites will aid in improving quantitative microbial risk assessment (QMRA) and infection control. The variability in SRE as a function of fomite type, fomite surface area, sampling time, application media, relative humidity (rH), and wetting agent was evaluated. To quantify the SRE, bacteriophage P22 was applied onto fomites at average surface densities of 0.4±0.2 and 4±2 PFU/cm2. Surface areas of 100 and 1,000 cm2 of nonporous fomites found in indoor environments (acrylic, galvanized steel, and laminate) were evaluated with premoistened antistatic wipes. The parameters with the most effects on the SRE were sampling time, fomite surface area, wetting agent, and rH. At time zero (the initial application of bacteriophage P22), the SRE for the 1,000-cm2 fomite surface area was, on average, 40% lower than that for the 100-cm2 fomite surface area. For both fomite surface areas, the application medium Trypticase soy broth (TSB) and/or the laminate fomite predominantly resulted in a higher SRE. After the applied samples dried on the fomites (20 min), the average SRE was less than 3%. A TSB wetting agent applied on the fomite improved the SRE for all samples at 20 min. In addition, an rH greater than 28% generally resulted in a higher SRE than an rH less than 28%. The parameters impacting SRE at the limit of detection have the potential to enhance sampling strategies and data collection for QMRA models. © 2012, American Society for Microbiology.
• Hewitt, K. M., Gerba, C. P., Maxwell, S. L., & Kelley, S. T. (2012). Office space bacterial abundance and diversity in three metropolitan areas. PLoS ONE, 7(5).
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  PMID: 22666400;PMCID: PMC3364274;Abstract: People in developed countries spend approximately 90% of their lives indoors, yet we know little about the source and diversity of microbes in built environments. In this study, we combined culture-based cell counting and multiplexed pyrosequencing of environmental ribosomal RNA (rRNA) gene sequences to investigate office space bacterial diversity in three metropolitan areas. Five surfaces common to all offices were sampled using sterile double-tipped swabs, one tip for culturing and one for DNA extraction, in 30 different offices per city (90 offices, 450 total samples). 16S rRNA gene sequences were PCR amplified using bar-coded "universal" bacterial primers from 54 of the surfaces (18 per city) and pooled for pyrosequencing. A three-factorial Analysis of Variance (ANOVA) found significant differences in viable bacterial abundance between offices inhabited by men or women, among the various surface types, and among cities. Multiplex pyrosequencing identified more than 500 bacterial genera from 20 different bacterial divisions. The most abundant of these genera tended to be common inhabitants of human skin, nasal, oral or intestinal cavities. Other commonly occurring genera appeared to have environmental origins (e.g., soils). There were no significant differences in the bacterial diversity between offices inhabited by men or women or among surfaces, but the bacterial community diversity of the Tucson samples was clearly distinguishable from that of New York and San Francisco, which were indistinguishable. Overall, our comprehensive molecular analysis of office building microbial diversity shows the potential of these methods for studying patterns and origins of indoor bacterial contamination. "[H]umans move through a sea of microbial life that is seldom perceived except in the context of potential disease and decay." - Feazel. (2009). © 2012 Hewitt et al.
• Ikner, L. A., Gerba, C. P., & Bright, K. R. (2012). Concentration and Recovery of Viruses from Water: A Comprehensive Review. Food and Environmental Virology, 4(2), 41-67.
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  PMID: 23412811;Abstract: Enteric viruses are a cause of waterborne disease worldwide, and low numbers in drinking water can present a significant risk of infection. Because the numbers are often quite low, large volumes (100-1,000 L) of water are usually processed. The VIRADEL method using microporous filters is most commonly used today for this purpose. Negatively charged filters require the addition of multivalent salts and acidification of the water sample to effect virus adsorption, which can make large-volume sampling difficult. Positively charged filters require no preconditioning of samples, and are able to concentrate viruses from water over a greater pH range than electronegative filters. The most widely used electropositive filter is the Virosorb 1MDS; however, the Environmental Protection Agency has added the positively charged NanoCeram filters to their proposed Method 1615. Ultrafilters concentrate viruses based on size exclusion rather than electrokinetics, but are impractical for field sampling or processing of turbid water. Elution (recovery) of viruses from filters following concentration is performed with organic (e. g., beef extract) or inorganic solutions (e. g., sodium polyphosphates). Eluates are then reconcentrated to decrease the sample volume to enhance detection methods (e. g., cell culture infectivity assays and molecular detection techniques). While the majority of available filters have demonstrated high virus retention efficiencies, the methods to elute and reconcentrate viruses have met with varying degrees of success due to the biological variability of viruses present in water. © 2012 Springer Science + Business Media, LLC.
• Nordstrom, J. M., Reynolds, K. A., & Gerba, C. P. (2012). Comparison of bacteria on new, disposable, laundered, and unlaundered hospital scrubs. American Journal of Infection Control, 40(6), 539-543.
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  PMID: 22177668;Abstract: Background: As a cost-saving measure, an increasing number of hospitals allow personnel to launder their uniforms, lab coats, and operating room scrubs at home. With rising nosocomial infection rates and increasing levels of multidrug-resistant bacteria in hospital settings, uniform contamination may be an environmental factor in the spread of infection. Methods: We quantified the number and identity of bacteria found on swatches cut from unwashed operating room, hospital-laundered, home-laundered, new cloth, and new disposable scrubs. Results: Of the 29 unwashed hospital operating room scrub swatches analyzed, 23 (79%) were positive for some type of gram-positive cocci, with 3 (10%) of those classified as Staphylococcus aureus, and 20 (69%) were positive for coliform bacteria, 3 of which were Escherichia coli. Home-laundered scrubs had a significantly higher total bacteria count than hospital-laundered scrubs (P =.016). There was no statistical difference in the bacteria counts between hospital-laundered scrubs and unused new and disposable scrubs. In the home-laundered scrubs 44% (18/41) were positive for coliform bacteria, but no isolates were Escherichia coli. Conclusions: Significantly higher bacteria counts were isolated from home-laundered scrubs and unwashed scrubs than from new, hospital-laundered, and disposable scrubs. Copyright © 2012 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.
• Reynolds, K. A., Boone, S., Bright, K. R., & Gerba, C. P. (2012). Occurrence of household mold and efficacy of sodium hypochlorite disinfectant. Journal of Occupational and Environmental Hygiene, 9(11), 663-669.
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  PMID: 23016564;Abstract: The occurrence and distribution of mold on household surfaces and the efficacy of bleach-based (sodium hypochlorite, NaOCl) disinfectants on mold viability and allergenicity was documented. Household microenvironments prone to increased moisture were specifically targeted. Using the sticky tape method, 1330 samples were collected from non-porous indoor surfaces of 160 homes across the United States, and analyzed for mold. Homes were randomly selected and recruited via phone interviews. Culture and immunoassays were used to measure the viability and reduction of allergenic properties of Aspergillus fumigatus following 2.4% NaOCl treatment. All homes and 72.9% of surfaces tested positive for mold. Windowsills were the most frequently contaminated site (87.5%) and Cladosporium the most commonly identified mold (31.0%). Five-minute exposures to 2.4% NaOCl resulted in a >3 to >6-log10 reduction of culturable mold counts in controlled laboratory studies. Organisms were nonculturable after 5-and 10-min contact times on non-porous and porous ceramic carriers, respectively, and A. fumigatus spore-eluted allergen levels were reduced by an average 95.8% in 30 sec, as indicated by immunoassay. All homes are contaminated with some level of mold, and regrowth is likely in moisture-prone microenvironments. The use of low concentrations (2.4%) of NaOCl for the reduction of culturable indoor mold and related allergens is effective and recommended. Copyright © 2012 JOEH, LLC.
• Rodríguez, R. A., Gundy, P. M., Rijal, G. K., & Gerba, C. P. (2012). The Impact of Combined Sewage Overflows on the Viral Contamination of Receiving Waters. Food and Environmental Virology, 4(1), 34-40.
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  PMID: 23412766;Abstract: The contribution of combined sewer overflows (CSO) to the viral contamination of receiving waters was determined. Adenovirus concentrations were determined using the Primary Liver Carcinoma (PLC/PRF/5) cell line and confirmed by Polymerase Chain Reaction (PCR). Norovirus concentration was determined using the Most Probable Number (MPN) and Reverse Transcription-Polymerase Chain Reaction (RT-PCR). Seventy-five water samples were collected during dry weather and 50 samples were collected during wet weather. CSO events significantly increased the concentration of culturable viruses, adenoviruses, and noroviruses in the receiving waters (P < 0.01). During dry weather, 56% of samples were positive for total virus cytopathic effects (CPE), adenoviruses were detected in 41% of the positive cell cultures, and noroviruses in 6% of the concentrates by direct RT-PCR. During wet weather, 100% of the samples were positive by CPE, 84% for adenoviruses, and 40% in the concentrates for norovirus. Our results demonstrate that CSOs can contribute significant viral loading to receiving waters. © 2012 Springer Science + Business Media, LLC.
• Santamaría, J., Brusseau, M. L., Araujo, J., Orosz-Coghlan, P., Blanford, W. J., & Gerba, C. P. (2012). Transport and retention of Cryptosporidium Parvum oocysts in sandy soils. Journal of Environmental Quality, 41(4), 1246-1252.
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  PMID: 22751068;Abstract: A series of miscible-displacement experiments was conducted to examine the retention and transport behavior of Cryptosporidium parvum oocysts in natural porous media. Th ree soils and a model sand were used that differed in physical and geochemical properties. Transport behavior was examined under various treatment conditions to help evaluate retention mechanisms. Significant retention of Cryptosporidium oocysts was observed for all media despite the fact that conditions were unfavorable for physicochemical interactions with respect to DLVO theory. Th e magnitude of Cryptosporidium retention was not influenced significantly by alterations in solution chemistry (reduction in ionic strength) or soil surface properties (removal of soil organic matter and metal oxides). On the basis of the observed results, it appears that retention by secondary energy minima or geochemical microdomains was minimal for these systems. Th e porous media used for the experiments exhibited large magnitudes of surface roughness, and it is suggested that this surface roughness contributed significantly to oocyst retention. © 2012 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
• Sarkar, P., & Gerba, C. P. (2012). Erratum: Inactivation of Naegleria fowleri by Chlorine and ultraviolet light (Journal - American Water Works Association (2012)). Journal - American Water Works Association, 104(4), 95-.
• Sarkar, P., & Gerba, C. P. (2012). Inactivation of Naegleria fowleri by chlorine and ultraviolet light. Journal - American Water Works Association, 104(3), 51-52.
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  Abstract: Naegleria fowleri is a free-living protozoa that causes the fatal disease primary amoebic meningoencephalitis; the only cases associated with drinking water have occurred in Australia and Arizona. A recent study found N. fowleri in 8% (n = 143) of all municipal untreated drinking water wells tested. The C × T (concentration × exposure time) values for chlorine inactivation of N. fowleri trophozoites and cysts at an average disinfectant concentration of 1 mg/L were determined using the efficiency factor Hom model. The estimated C × T values for N. fowleri cysts are comparable to the published values for Giardia cysts, but are lower than those for Cryptosporidium oocysts. In this study, the ultraviolet light dosage required for the inactivation of the cyst stage of N. fowleri was determined to be greater than that of Cryptosporidium oocysts but less than that of Acanthamoeba cysts.
• Sinclair, R. G., Rose, J. B., Hashsham, S. A., Gerba, C. P., & Haase, C. N. (2012). Criteria for selection of surrogates used to study the sate and control of pathogens in the environment. Applied and Environmental Microbiology, 78(6), 1969-1977.
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  PMID: 22247166;PMCID: PMC3298155;Abstract: This article defines the term surrogate as an organism, particle, or substance used to study the fate of a pathogen in a specific environment. Pathogenic organisms, nonpathogenic organisms, and innocuous particles have been used as surrogates for a variety of purposes, including studies on survival and transport as well as for method development and "indicators" of certain conditions. This article deasvelops a qualitative surrogate attribute prioritization process and allows investigators to select a surrogate by systematically detailing the experimental process and prioritizing attributes. The results are described through the use of case studies of various laboratories that have used this process. This article also discusses the history of surrogate and microbial indicator use and outlines the method by which surrogates can be used when conducting a quantitative microbial risk assessment. The ultimate goal of selecting a sufficiently representative surrogate is to improve public health through a health-based risk assessment framework. Under- or overestimating the resistance, inactivation, or movement may negatively impact risk assessments that, in turn, will impact health assessments and estimated safety levels. Reducing uncertainty in a risk assessment is one of the objectives of using surrogates and the ultimate motive for any experiment investigating potential exposure of a pathogen. © 2012, American Society for Microbiology.
• Vidales-Contreras, J. A., Gerba, C. P., Karpiscak, M. M., Valdez-Cepeda, R. D., & Hernandez-Escareo, J. J. (2012). Transport and removal of coliphage PRD1 in constructed wetlands. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 47(1), 142-148.
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  PMID: 22217092;Abstract: The Convection Dispersion Equation (CDE) was used to calculate PRD1 and Br transport parameters in a subsurface flow constructed wetland. Transport parameters from Br - displacement were applied into the CDE to estimate a 0.96 day -1 first order decay coefficient (k). The PRD1 breakthrough curves were also simulated to obtain effective cross-sectional area (Ac), longitudinal dispersion coefficient (D), convective velocity (v), and k. There was practically no difference between Ac and D for both tracers. However, the estimated convective velocity was higher for PRD1 than for Br -. Further simulations were conducted by taking experimental concentrations from prior research on surface and subsurface flow constructed wetlands. Dispersion number (d) was estimated to be between 0.17 and 0.029 by using PRD1 and Br - transport parameters. These parameters were also used to calculate wetland dimensionless removal (K). An analytical solution for the zero moment of the observed breakthrough curves was applied to estimate PRD1 fraction recoveries in the wetland by using d and K. The results of the present study suggest that this analytical solution may be an alternative design tool for pathogen removal estimation in subsurface flow constructed wetlands. © 2012 Copyright Taylor and Francis Group, LLC.
• Alum, A., Enriquez, C., & Gerba, C. (2011). Impact of drip irrigation method, soil, and virus type on tomato and cucumber contamination. Food Environ. Virol, 3, 78-81.
• Alum, A., Enriquez, C., & Gerba, C. P. (2011). Impact of Drip Irrigation Method, Soil, and Virus Type on Tomato and Cucumber Contamination. Food and Environmental Virology, 3(2), 78-85.
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  Abstract: The goal of this study was to better quantify the degree of viral contamination of tomato and cucumber in relationship to virus type, soil type, and irrigation method. Tomatoes and cucumbers were grown in ten-gallon (37.8 L) buckets filled with Pima clay loam or Brazito sandy loam soils. Plants were irrigated with secondary wastewater effluent using surface drip irrigation or subsurface drip irrigation. At specified time intervals irrigation water was seeded with bacteriophages MS-2 and P22, poliovirus type 1 (PV1), enteric adenovirus 40 (Ead 40), and hepatitis A virus. Surface drip irrigation always resulted in viral contamination of both the above and below ground parts of both crops. The roots showed the greatest level of contamination, followed by leaves and fruits. In contrast, with subsurface drip irrigation no viruses were detected in any of the above ground plant surfaces. It was found that under similar soil type and irrigation method, risk of crop contamination was similar for all of the viruses studied. It can be concluded that method of irrigation is the single most critical factor in the contamination trend of different parts of crop plants. Plant parts can be categorized into three groups (root, stem, and leaf/fruit) based on the risk of viral contamination from irrigation water. © 2011 Springer Science + Business Media, LLC.
• Chattman, M., Maxwell, S. L., & Gerba, C. P. (2011). Occurrence of heterotrophic and coliform bacteria in liquid hand soaps from bulk refillable dispensers in public facilities. Journal of Environmental Health, 73(7), 26-29.
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  PMID: 21413559;Abstract: The goal of the study discussed in this article was to determine the occurrence of heterotrophic and coliform bacteria in liquid soap from bulk refutable dispensers, obtained from restrooms in a variety of public facilities. A total of 541 samples was collected from five U.S. cities. Liquid soap from dispensers in public areas was found to contain heterotrophic and coliform bacterial numbers averaging more than 106 CFLU/mL in 24.8% of the dispensers.
• Chattman, M., Maxwell, S., & Gerba, C. (2011). Occurrence of heterotrophic and coliform bacteria in liquid hand soaps from bulk refillable dispensers in public facilities.
• Gerba, C. P., Tamimi, A. H., Pettigrew, C., Weisbrod, A. V., & Rajagopalan, V. (2011). Sources of microbial pathogens in municipal solid waste landfills in the United States of America. Waste Management and Research, 29(8), 781-790.
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  PMID: 21382871;Abstract: Municipal solid waste (MSW) categories, as specified by United States Environmental Protection Agency (US EPA), were evaluated for their relative contribution of pathogenic viruses, bacteria, and protozoan parasites into MSW landfills from 1960 to 2007. The purpose of this study was to identify trends and quantify the potential contribution of pathogens in MSW as an aid to the assessment of potential public health risks. A review of the literature was conducted to estimate values for the concentrations of faecal indicator bacteria and pathogens in the major categories of MSW. The major sources of MSW contributing enteric pathogens were food waste, pet faeces, absorbent products, and biosolids. During the last 47 years, recycling of glass, metals, plastic, paper and some organic wastes in MSW has increased, resulting in a decreased proportion of these materials in the total landfilled MSW. The relative proportion of remaining waste materials has increased; several of these waste categories contain pathogens. For all potential sources, food waste contributes the greatest number of faecal coliforms (80.62%). The largest contribution of salmonellae (97.27%), human enteroviruses (94.88%) and protozoan parasites (97%) are expected to come from pet faeces. Biosolids from wastewater treatment sludge contribute the greatest number of human noroviruses (99.94%). By comparison, absorbent hygiene products do not appear to contribute significantly to overall pathogen loading for any group of pathogens. This is largely due to the relatively low volume of these pathogen sources in MSW, compared, for example, with food waste at almost 40% of total MSW. © 2011 The Author(s).
• Gerba, C., & HPC, . (2011). Microbial risk assessment as a tool in predicting outcomes of hygiene interventions. HPC and Compendium on Detergency, 2, 4-6.
• Gerba, C., Ross, A., Takizawa, K., & Pepper, I. (2011). Efficiency of the method D4994-89 for recovery of enteric viruses from biosolids. Food Environ. Virol., 3, 43-45.
• Gerba, C., Sexton, J. D., Tanner, B. D., Maxwell, S. L., & Gerba, C. P. (2011). Reduction in the microbial load on high-touch surfaces in hospital rooms by treatment with a portable saturated steam vapor disinfection system. American journal of infection control, 39(8).
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  Recent scientific literature suggests that portable steam vapor systems are capable of rapid, chemical-free surface disinfection in controlled laboratory studies. This study evaluated the efficacy of a portable steam vapor system in a hospital setting.
• Gerba, C., Tamimi, A., Pettigrew, C., Weisbrod, A., & Rajagopalan, V. (2011). Sources of microbial pathogens in municipal solid waste in the United States of America. Waste Management and Research, 29, 781-790.
• Gortares-Moroyoqui, P., Castro-Espinoza, J., Naranjo, M., Karpiscak, R., Frieitas, ., & Gerba, C. (2011). Microbiological quality in a large irrigation system: El Valle del Yaqui, Sonora, Mexico. J. Environ. Sci. Hlth, Part A, 46, 1708-1712.
• Gortáres-Moroyoqui, P., Castro-Espinoza, L., Naranjo, J. E., Karpiscak, M. M., Freitas, R. J., & Gerba, C. P. (2011). Microbiological water quality in a large irrigation system: El valle del yaqui, Sonora México. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 46(14), 1708-1712.
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  PMID: 22175874;Abstract: The primary objective of this study was to determine the microbial water quality of a large irrigation system and how this quality varies with respect to canal size, impact of near-by communities, and the travel distance from the source in the El Valle del Yaqui, Sonora, México. In this arid region, 220,000 hectares are irrigated with 80% of the irrigation water being supplied from an extensive irrigation system including three dams on the Yaqui River watershed. The stored water flows to the irrigated fields through two main canal systems (severing the upper and lower Yaqui Valley) and then through smaller lateral canals that deliver the water to the fields. A total of 146 irrigation water samples were collected from 52 sample sites during three sampling events. Not all sites could be accessed on each occasion. All of the samples contained coliform bacteria ranging from 1,140 to 68,670 MPN/100 mL with an arithmetic mean of 11,416. Ninety-eight percent of the samples contained less than 1,000 MPN/100 mL Escherichia coli, with an arithmetic mean of 291 MPN/100 mL. Coliphage were detected in less than 30% of the samples with an arithmetic average equal to 141 PFU/100 mL. Enteroviruses, Cryptosporidium oocysts, and Giardia cysts were also etected in the canal systems. No significant difference was found in the water quality due to canal system (upper or lower Yaqui Valley), canal-size (main vs. lateral), distance from source, and the vicinity of human habitation (presence of various villages and towns along the length of the canals). There was a significant decrease in coliforms (p < 0.011) and E. coli (
• Medrano-Félix, A., Martínez, C., Campo, N. C., León-Félix, J., Peraza-Garay, F., Gerba, C. P., & Chaidez, C. (2011). Impact of prescribed cleaning and disinfectant use on microbial contamination in the home. Journal of Applied Microbiology, 110(2), 463-471.
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  PMID: 21143709;Abstract: Aims: To identify and quantify the presence of Escherichia coli, Staphylococcus aureus, Salmonella, hepatitis A and norovirus in households and to assess the effect of chlorine and quaternary ammonium-based disinfectants following a prescribed use.Methods and Results: Eleven sites distributed in kitchen, bathroom, pet and children's areas of two groups of 30 homes each: (i) a nonprescribed disinfectant user group and (ii) a disinfectant protocol user group. During the 6-week study, samples were collected once a week except for week one when sample collection occurred immediately before and after disinfectant application to evaluate the disinfectant protocol. The concentration and occurrence of bacteria were less in the households with prescribed use of disinfectants. The greatest reductions were for E. coli (99%) and Staph. aureus (99·9999%), respectively. Only two samples were positive for HAV, while norovirus was absent. Disinfection protocols resulted in a significant (P
• Miles, S., Takizawa, I., Pepper, L., & Gerba, C. (2011). Survival of infectious prions in biosolids. J. Eviron. Sci. Hlth : Part A, 46, 1-7.
• Miles, S., Takizawa, K., Gerba, C., & Pepper, I. (2011). Survival of prions in water. J. Environ. Hlth, 46, 938-943.
• Onyango-Ouma, W., & Gerba, C. (2011). Away-from-home drinking water consumption practices and the microbiological quality of water consumed in rural western Kenya. J. Water Hlth, 9, 628-636.
• Onyango-Ouma, W., & Gerba, C. P. (2011). Away-from-home drinking water consumption practices and the microbiological quality of water consumed in rural western Kenya. Journal of Water and Health, 9(4), 628-636.
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  PMID: 22048422;Abstract: A cross-sectional descriptive study was conducted to examine away-from-home drinking water consumption practices and the microbiological quality of water consumed in rural western Kenya. The study involved adults and schoolchildren. Data were collected using focus group discussions, questionnaire survey, observations, diaries and interviews. The findings suggest that away-from-home drinking water consumption is a common practice in the study area; however, the microbiological quality of the water consumed is poor. While some respondents perceive the water to be safe for drinking mainly because of the clear colour of the water, others are forced by circumstances to drink the water as it is owing to a lack of alternative safe sources. It is concluded that there is a need for new innovative approaches to address away-from-home drinking water consumption in resource-poor settings in order to complement and maximize the benefits of point-of-use water treatment at the household level. © IWA Publishing 2011.
• Rijal, G., Tolson, J. K., Petropoulou, C., Granato, T. C., Glymph, A., Gerba, C., Deflaun, M. F., O'Connor, C., Kollias, L., & Lanyon, R. (2011). Microbial risk assessment for recreational use of the Chicago Area Waterway System. Journal of Water and Health, 9(1), 169-186.
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  PMID: 21301125;Abstract: A microbial risk assessment was conducted to estimate the human health risks from incidental contact recreational activities such as canoeing, boating and fishing in the Chicago Area Waterway System (CAWS) receiving secondary treated, but non-disinfected, effluent from three municipal water reclamation plants. Actual concentrations of the pathogens (pathogenic E. coli [estimated], Giardia, Cryptosporidium, adenovirus, norovirus, enteric virus) detected from the waterway field data collection at locations upstream and downstream of the effluent outfall during dry and wet weather conditions within the recreation season were included in the risk assessment. The results under the current treatment scheme with no disinfection indicated that the total expected gastrointestinal illness (GI) rate per 1000 incidental contact recreational exposure events during combined weather (dry and wet) conditions ranged from 0.10 to 2.78 in the CAWS, which is below the eight illnesses per 1000 swimmers considered tolerable by the United States Environmental Protection Agency. Wet weather conditions contribute to elevated pathogen load to the CAWS; therefore this study determined that disinfecting the effluents of three major WRPs that discharge to the CAWS would result in an extremely small reduction in the aggregate recreation season risk to incidental contact recreators.
• Rijal, G., Tolson, J., Petropoulou, C., Granato, T., Glymph, A., Gerba, C., Deflaun, M., O, C. C., Kollias, L., & Lanyon, R. (2011). Microbial risk assessment for recreational use in the Chicago area waterway system. Water Hlth., 9, 169-186.
• Riley, M. R., Gerba, C. P., & Elimelech, M. (2011). Biological approaches for addressing the grand challenge of providing access to clean drinking water. Journal of Biological Engineering, 5.
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  PMID: 21453515;PMCID: PMC3080283;Abstract: The U.S. National Academy of Engineering (NAE) recently published a document presenting Grand Challenges for Engineering. This list was proposed by leading engineers and scientists from around the world at the request of the U.S. National Science Foundation (NSF). Fourteen topics were selected for these grand challenges, and at least seven can be addressed using the tools and methods of biological engineering. Here we describe how biological engineers can address the challenge of providing access to clean drinking water. This issue must be addressed in part by removing or inactivating microbial and chemical contaminants in order to properly deliver water safe for human consumption. Despite many advances in technologies this challenge is expanding due to increased pressure on fresh water supplies and to new opportunities for growth of potentially pathogenic organisms. © 2011 Riley et al; licensee BioMed Central Ltd.
• Riley, M., Gerba, C., & Elimelech, M. (2011). Biological approaches for addressing the grand challenge of providing access to clean drinking water. J. Biological Engr, 5(2), 1-10.
• Santamaris, J., Quinonez-Diasz, M., LeMond, L., Arnold, R., Quanrud, D., Gerba, C., & Brusseau, M. (2011). Transport of Cryptosporidium parvum oocysts in sandy soil: Impact of length scale. J. Environ. Monitoring, 13, 3481-3484.
• Sexton, J. D., Tanner, B. D., Maxwell, S. L., & Gerba, C. P. (2011). Reduction in the microbial load on high-touch surfaces in hospital rooms by treatment with a portable saturated steam vapor disinfection system. American Journal of Infection Control, 39(8), 655-662.
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  PMID: 21641089;Abstract: Background: Recent scientific literature suggests that portable steam vapor systems are capable of rapid, chemical-free surface disinfection in controlled laboratory studies. This study evaluated the efficacy of a portable steam vapor system in a hospital setting. Methods: The study was carried out in 8 occupied rooms of a long-term care wing of a hospital. Six surfaces per room were swabbed before and after steam treatment and analyzed for heterotrophic plate count (HPC), total coliforms, methicillin-intermediate and -resistant Staphylococcus aureus (MISA and MRSA), and Clostridium difficile. Results: The steam vapor device consistently reduced total microbial and pathogen loads on hospital surfaces, to below detection in most instances. Treatment reduced the presence of total coliforms on surfaces from 83% (40/48) to 13% (6/48). Treatment reduced presumptive MISA (12/48) and MRSA (3/48) to below detection after cleaning, except for 1 posttreatment isolation of MISA (1/48). A single C difficile colony was isolated from a door push panel before treatment, but no C difficile was detected after treatment. Conclusion: The steam vapor system reduced bacterial levels by >90% and reduced pathogen levels on most surfaces to below the detection limit. The steam vapor system provides a means to reduce levels of microorganisms on hospital surfaces without the drawbacks associated with chemicals, and may decrease the risk of cross-contamination. Copyright © 2011 by the Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc. All rights reserved.
• Sexton, J., Tanner, B., Maxwell, S., & Gerba, C. (2011). Reduction in the microbial load on high-touch surfaces in hospital rooms by treatment with a portable saturated steam vapor disinfection system. Am. J. Infect. Control, 39, 655-662.
• Sinclair, R. G., & Gerba, C. P. (2011). Microbial contamination in kitchens and bathrooms of rural Cambodian village households. Letters in Applied Microbiology, 52(2), 144-149.
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  PMID: 21198693;Abstract: Aims: To quantify microbial contamination on kitchen and bathroom surfaces (fomites) in rural Cambodian homes and to compare these concentrations to similar data from the United States and Japan.Methods and Results: This study monitored the numbers of faecal coliforms (i.e. thermotolerant coliforms), total coliforms, Escherichia coli and heterotrophic plate count bacteria on household surfaces in a rural village of Cambodia. Faecal coliform levels in Cambodia were highest on moist locations such as the plastic ladle used for sink water, the toilet seat surface and the cutting board surface with 100-fold higher levels of faecal coliform bacteria than E. coli and 100-fold higher levels of faecal coliforms than the US and Japanese studies.Conclusions: A single public health intervention barrier, such as an improved latrine, is only partially effective for household sanitation. For complete sanitation, multiple environmental barriers may be necessary. These barriers occur in a house constructed with easily washable surfaces, a chlorinated water distribution system, house climate control and cleaning product availability.Significance and Impact of the Study: Results of this study can be used to emphasize the importance of increasing household environmental sanitation barriers. © 2010 The Authors. Letters in Applied Microbiology © 2010 The Society for Applied Microbiology.
• Sinclair, R., & Gerba, C. (2011). Microbial contamination in kitchens and bathrooms of rural Cambodian village homes. Letters in Appl. Microbiol., 52, 144-149.
• Stine, S. W., Song, I., Choi, C. Y., & Gerba, C. P. (2011). Application of Pesticide Sprays to Fresh Produce: A Risk Assessment for Hepatitis A and Salmonella. Food and Environmental Virology, 3(2), 86-91.
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  Abstract: The purpose of this study was to quantify the transfer of viral and bacterial pathogens in water used to dilute pesticides sprayed onto the surfaces of cantaloupe, iceberg lettuce, and bell peppers. The average percent transfer of bacteria was estimated to range from 0.00021 to 9.4%, while average viral transfer ranged from 0.055 to 4.2%, depending on the type of produce. Based on these values the concentrations of hepatitis A virus (HAV) and Salmonella in water necessary to achieve a 1:10,000 annual risk of infection were calculated. Under worst case scenario assumptions, in which a pesticide is applied on the same day that the produce is harvested and when maximum transfer values are used, concentrations of 1.5 × 10-3 CFU Salmonella or 2.7 × 10-7 MPN HAV per 100 ml of the water used for application would result in 1:10,000 annual infection risk to anyone who consumes the fresh produce. If harvesting does not occur until at least 14 days after the application, to produce the same risk of infection, the numbers of Salmonella in 100 ml of water used to dilute the pesticides will be greater by up to five orders of magnitude, while the HAV numbers will have increased by up to two orders of magnitude. Based on the reported concentrations of enteric viruses in surface and ground waters in the United States, a 1:10,000 annual risk of infection could easily be exceeded with some groundwater sources used in the United States. To reduce the risks associated with the consumption of fresh produce, water used to prepare pesticides in spray applications should be evaluated for its microbiological quality. © 2011 Springer Science + Business Media, LLC.
• Stine, S., Song, I., Choi, C., & Gerba, C. (2011). Application of pesticide sprays to fresh produce: a risk assessment for hepatitis A and Salmonella. Food Environ. Virol, 3, 86-91.
• Vidales-Contreras, J., Gerba, C. P., Karpisack, M. M., Rodríguez-Fuentes, H., Chaidez-Quiroz, C., & Olivares-Sáenz, E. (2011). Performance of a surface flow constructed wetland system used to treat secondary effluent and filter backwash water. Tropical and Subtropical Agroecosystems, 14(2), 375-384.
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  Abstract: The performance of a surface flow wetland system used to treat activated sludge effluent and filter backwash water from a tertiary treatment facility was evaluated. Samples were collected before and after vegetation removal from the system which consists of two densely vegetated settling basins (0.35 ha), an artificial stream, and a 3-ha surface flow wetland. Bulrush (Scripus spp.) and cattail (Typha domingensis) were the dominant plant species. The average inflow of chlorinated secondary effluent during the first two months of the actual study was 1.9 m3 min-1 while the inflow for backwash water treatment ranged from 0.21 to 0.42 m3 min-1. The system was able to reduce TSS and BOD5 to tertiary effluent standards; however, monitoring of chloride concentrations revealed that wetland evapotranspiration is probably enriching pollutant concentrations in the wetland outflow. Coliphage removal from the filter backwash was 97 and 35% during 1999 and 2000, respectively. However, when secondary effluent entered the system, coliphage removal averaged 65%. After vegetation removal, pH and coliphage density increased significantly (p
• Williams, D. L., Gerba, C. P., Maxwell, S., & Sinclair, R. G. (2011). Assessment of the potential for cross-contamination of food products by reusable shopping bags. Food Protection Trends, 31(8), 508-513.
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  Abstract: The purpose of this study was to assess the potential for cross-contamination of food products by reusable bags used to carry groceries. Reusable bags were collected at random from consumers as they entered grocery stores in California and Arizona. In interviews, it was found that reusable bags are seldom if ever washed and often used for multiple purposes. Large numbers of bacteria were found in almost all bags and coliform bacteria in half. Escherichia coli were identified in 8% of the bags, as well as a wide range of enteric bacteria, including several opportunistic pathogens. When meat juices were added to bags and stored in the trunks of cars for two hours, the number of bacteria increased 10-fold, indicating the potential for bacterial growth in the bags. Hand or machine washing was found to reduce the bacteria in bags by > 99.9%. These results indicate that reusable bags, if not properly washed on a regular basis, can play a role in the cross-contamination of foods. It is recommended that the public be educated about the proper care of reusable bags by means of printed instructions on the bags or through public service announcements. Copyright© 2011, International Association for Food Protection.
• Williams, D., Gerba, C., Maxwell, S., & Sinclair, R. (2011). Assessment of the potential for cross-contamination of food products by reusable shopping bags. Food Protect Trends, 31, 508-513.
• Zapata, C., Campbell, E., Maxwell, S., Gerba, C., Doyle, M., Arbogast, J., & Macina, D. (2011). Bacterial hand contamination and transfer after use of contaminated bulk-soap-refillable dispensers. Appl. Environ. Microbiol, 77, 2898-2904.
• Zapka, C. A., Campbell, E. J., Maxwell, S. L., Gerba, C. P., Dolan, M. J., Arbogast, J. W., & Macinga, D. R. (2011). Bacterial hand contamination and transfer after use of contaminated bulk-soap-refillable dispensers. Applied and Environmental Microbiology, 77(9), 2898-2904.
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  PMID: 21421792;PMCID: PMC3126420;Abstract: Bulk-soap-refillable dispensers are prone to extrinsic bacterial contamination, and recent studies demonstrated that approximately one in four dispensers in public restrooms are contaminated. The purpose of this study was to quantify bacterial hand contamination and transfer after use of contaminated soap under controlled laboratory and in-use conditions in a community setting. Under laboratory conditions using liquid soap experimentally contaminated with 7.51 log10 CFU/ml of Serratia marcescens, an average of 5.28 log10 CFU remained on each hand after washing, and 2.23 log10 CFU was transferred to an agar surface. In an elementary-school-based field study, Gram-negative bacteria on the hands of students and staff increased by 1.42 log10 CFU per hand (26-fold) after washing with soap from contaminated bulk-soap-refillable dispensers. In contrast, washing with soap from dispensers with sealed refills significantly reduced bacteria on hands by 0.30 log10 CFU per hand (2-fold). Additionally, the mean number of Gram-negative bacteria transferred to surfaces after washing with soap from dispensers with sealed-soap refills (0.06 log10 CFU) was significantly lower than the mean number after washing with contaminated bulk-soap-refillable dispensers (0.74 log10 CFU; P < 0.01). Finally, significantly higher levels of Gram-negative bacteria were recovered from students (2.82 log10 CFU per hand) than were recovered from staff (2.22 log10 CFU per hand) after washing with contaminated bulk soap (P < 0.01). These results demonstrate that washing with contaminated soap from bulk-soaprefillable dispensers can increase the number of opportunistic pathogens on the hands and may play a role in the transmission of bacteria in public settings. © 2011, American Society for Microbiology.
• Boone, S. A., & Gerba, C. P. (2010). The prevalence of human parainfluenza virus 1 on indoor office fomites. Food and Environmental Virology, 2(1), 41-46.
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  Abstract: The objective of this study was to evaluate the potential role of fomites in human parainfluenza virus 1 (HPIV1) transmission by assessing the occurrence of HPIV1 on surfaces in an adult setting (office). In 2004, a total of 328 fomites from 12 different office buildings in five different cities were evaluated for HPIV1 viral RNA. HPIV1 was isolated using reverse transcriptase-polymerase chain reaction (RT-PCR) and detected on 37% of all office fomites. HPIV1 RNA was frequently isolated on desk tops (47%), and infrequently isolated on light switches (19%). Data revealed a statistically significant difference between the percentage of HPIV1 positive fomites in office cubicles and conference rooms (Chi-square P < 0.011, Fisher's Exact P = 0.054). A statistically significantdifference was also found among positive fomites in different buildings (Chi-square P < 0.011). HPIV1 was consistently isolated on various indoor fomites in the 12 office buildings assessed during 2004, a low HPIV incident year. © 2010 Springer Science + Business Media, LLC.
• Bright, K. R., Boone, S. A., & Gerba, C. P. (2010). Occurrence of bacteria and viruses on elementary classroom surfaces and the potential role of classroom hygiene in the spread of infectious diseases. Journal of School Nursing, 26(1), 33-41.
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  PMID: 19903773;Abstract: The presence of microorganisms on common classroom contact surfaces (fomites) was determined to identify the areas most likely to become contaminated. Six elementary classrooms were divided into control and intervention groups (cleaned daily with a quaternary ammonium wipe) and tested for heterotrophic bacteria. Three classrooms were also tested for norovirus and influenza A virus. Frequently used fomites were the most contaminated; water fountain toggles, pencil sharpeners, keyboards, and faucet handles were the most bacterially contaminated; desktops, faucet handles, and paper towel dispensers were the most contaminated with viruses. Influenza A virus was detected on up to 50% and norovirus on up to 22% of surfaces throughout the day. Children in the control classrooms were 2.32 times more likely to report absenteeism due to illness than children in the intervention classrooms and were absent longer (on average). Improved classroom hygiene may reduce the incidence of infection and thus student absenteeism. © 2010 The Author(s).
• Gerba, C. P., Boone, S. A., & Bright, K. R. (2010). Occurrence of bacteria and viruses on elementary classroom surfaces and the potential role of classroom hygiene in the spread of infectious diseases. THE JOURNAL OF SCHOOL NURSING, 26(1), 33-41. doi:https://doi.org/10.1177/1059840509354383
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  The presence of microorganisms on common classroom contact surfaces (fomites) was determined to identify the areas most likely to become contaminated. Six elementary classrooms were divided into control and intervention groups (cleaned daily with a quaternary ammonium wipe) and tested for heterotrophic bacteria. Three classrooms were also tested for norovirus and influenza A virus. Frequently used fomites were the most contaminated; water fountain toggles, pencil sharpeners, keyboards, and faucet handles were the most bacterially contaminated; desktops, faucet handles, and paper towel dispensers were the most contaminated with viruses. Influenza A virus was detected on up to 50% and norovirus on up to 22% of surfaces throughout the day. Children in the control classrooms were 2.32 times more likely to report absenteeism due to illness than children in the intervention classrooms and were absent longer (on average). Improved classroom hygiene may reduce the incidence of infection and thus student absenteeism.
• Gerba, C., Bright, K. R., Boone, S. A., & Gerba, C. P. (2010). Occurrence of bacteria and viruses on elementary classroom surfaces and the potential role of classroom hygiene in the spread of infectious diseases. The Journal of school nursing : the official publication of the National Association of School Nurses, 26(1).
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  The presence of microorganisms on common classroom contact surfaces (fomites) was determined to identify the areas most likely to become contaminated. Six elementary classrooms were divided into control and intervention groups (cleaned daily with a quaternary ammonium wipe) and tested for heterotrophic bacteria. Three classrooms were also tested for norovirus and influenza A virus. Frequently used fomites were the most contaminated; water fountain toggles, pencil sharpeners, keyboards, and faucet handles were the most bacterially contaminated; desktops, faucet handles, and paper towel dispensers were the most contaminated with viruses. Influenza A virus was detected on up to 50% and norovirus on up to 22% of surfaces throughout the day. Children in the control classrooms were 2.32 times more likely to report absenteeism due to illness than children in the intervention classrooms and were absent longer (on average). Improved classroom hygiene may reduce the incidence of infection and thus student absenteeism.
• Kim, M., Gerba, C. P., & Choi, C. Y. (2010). Assessment of physically-based and data-driven models to predict microbial water quality in open channels. Journal of Environmental Sciences, 22(6), 851-857.
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  PMID: 20923096;Abstract: In the present study, a physically-based hydraulic modeling tool and a data-driven approach using artificial neural networks (ANNs) were evaluated for their ability to simulate the fate and transport of microorganisms in a water system. To produce reliable data, a pipe network was constructed and a series of experiments using a fecal coliform indicator (Escherichia coli 15597) was conducted. For the physically-based model, morphological (pipe size, link length, slope, etc.) and hydraulic (flow rate) conditions were used as input variables, and for ANNs, water quality parameters (conductivity, pH, and turbidity) were used. Both approaches accurately described the fate and transport of microorganisms (physically-based model: correlation coeffcient (R) in the range of 0.914 - 0.977 and ANNs: R in the range of 0.949 - 0.980), with the exception of one case at a low flow rate (q = 31.56 cm3/sec). This study also indicated that these approaches could be complementarily utilized to assess the vulnerability of water facilities and to establish emergency plans based on hypothetical scenarios. © 2010 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences.
• Suleiman, W., Gerba, C. P., Tamimi, A. H., Freitas, R. J., Sheraideh, A. A., & Hayek, B. (2010). Management practices of sludge and biosolid treatment and disposal in jordan. Journal of Residuals Science and Technology, 7(1), 63-67.
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  Abstract: The recent expansion of activated sludge treatment of domestic sewage in Jordan has resulted in approximately 85% of the population now served by this treatment process. A survey was conducted to assess the current management practices, volumes of biosolids being generated and the fate of the generated biosolids. Jordan is currently served by 18 wastewater treatment facilities (16 of which have been detailed in this study) generating about 300,000 m 3 of liquid sludge as well as 15,000 m3 of dewatered sludge annually. All wastewater treatment plants use solar drying bedsor/and thickening of sludge/biosolids before being hauled off for disposal. Most of the generated biosolids are disposed of at nearby landfills or stored on-site.Water Authority of Jordan costs to transport biosolids for disposal is slightly more than one million US dollars per year. Recent studies indicate that the biosolids are equivalent in metal and pathogen loads to that of Class B biosolids in the United States. Recent changes in Jordian regulations create the opportunity for beneficial use of these biosolids through land application. © 2010 DEStech Publications, Inc.
• Vidales-Contreras, J. A., Gerba, C. P., Karpiscak, M. M., Fuentes, H. R., Jaime, J., & Chaidez-Quiroz, C. (2010). Performance of a surface flow constructed wetland system used to treat secondary effluent and filter backwash water. International Journal of Agriculture and Biology, 12(6), 821-827.
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  Abstract: The performance of a surface flow wetland used to treat activated sludge effluent and filter backwash water from a tertiary treatment facility was evaluated. Samples were collected before and after vegetation removal from the wetland system, which consisted of two densely vegetated settling basins (0.35 ha), an artificial stream and a 3-ha surface flow wetland. Bulrush (Scripus spp.) and cattail (Typha domingensis) were the dominant plant species. The average inflow of chlorinated secondary effluent during the first two months of the actual study was 1.84 m3 min-1, while the inflow for backwash water treatment ranged from 0.21 to 0.42 m3 min-1. The system was able to reduce TSS and BOD5 to tertiary effluent standards; however, monitoring of chloride concentrations revealed that wetland evapotranspiration is probably enriching pollutant concentrations in the wetland outflow. Coliphage removal from the filter backwash was 97 and 35% during 1999 and 2000, respectively. However, when secondary effluent entered the system, coliphage removal averaged 65%. After vegetation removal, pH and coliphage density increased significantly (p
• Black, S., Thurston, J. A., & Gerba, C. P. (2009). Determination of Ct values for chlorine of resistant enteroviruses. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 44(4), 336-339.
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  PMID: 19184699;Abstract: Information on the required chlorine dose or Ct value (concentration of free chlorine multiplied by contact time) is limited to only a few enteroviruses. In this study the Ct values of some of the reported more chlorine resistant enteroviruses were determined. The Efficiency Hom Model was used to predict the times for 2, 3. and 4 -log inactivation of echovirus 1 and 12, coxsackievirus B5 and poliovirus type 1 at pH 7.5 and 9 at 5°C. Coxsackievirus B5 was the most resistant to chlorine with a Ct requirement of 11.5 mg×min/L at pH 7.5 at 5°C compared to polio with a Ct of 5.3 mg×min/L under the same conditions. All the viruses were more resistant than polio 1 at pH 9.0. Copyright © Taylor & Francis Group, LLC.
• Bright, K. R., Marciano-Cabral, F., & Gerba, C. P. (2009). Occurrence of Naegleria fowleri in Arizona drinking water supply wells. Journal / American Water Works Association, 101(11), 43-50.
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  Abstract: Naegleria fowleri is a protozoan found naturally in hot springs and warm surface waters. It can cause usually lethal primary amoebic meningoencephalitis. The goal of this study was to determine the occurrence of N. fowleri in drinking water supply wells in Arizona. Nested polymerase chain reaction was used to detect trophozoites and cysts, but not to assess viability. A total of 185 samples were collected from 113 wells before disinfection. The presence of N. fowleri deoxyribonucleic acid was confirmed in 10.6% of wells. No correlations were found between the presence of N. fowleri and heterotrophic bacteria, coliforms, Escherichia coli, temperature, specific conductance, or turbidity. N. fowleri was detected in 10.0% of initial and 17.2% of purged well samples, suggesting that N. fowleri may be present in the aquifer or detach from the well casing or pump column during pumping.
• Clasen, T., Naranjo, J., Frauchiger, D., & Gerba, C. (2009). Laboratory assessment of a gravity-fed ultrafiltration water treatment device designed for household use in low-income settings. American Journal of Tropical Medicine and Hygiene, 80(5), 819-823.
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  PMID: 19407130;Abstract: Interventions to improve water quality, particularly when deployed at the household level, are an effective means of preventing endemic diarrheal disease, a leading cause of mortality and morbidity in the developing world. We assessed the microbiologic performance of a novel water treatment device designed for household use in low-income settings. The device employs a backwashable hollow fiber ultrafiltration cartridge and is designed to mechanically remove enteric pathogenic bacteria, viruses, and protozoan cysts from drinking water without water pressure or electric power. In laboratory testing through 20,000 L (̃110% of design life) at moderate turbidity (15 nephelometric turbidity unit [NTU]), the device achieved log 10 reduction values of 6.9 for Escherichia coli, 4.7 for MS2 coliphage (proxy for enteric pathogenic viruses), and 3.6 for Cryptosporidium oocysts, thus exceeding levels established for microbiological water purifiers. With periodic cleaning and backwashing, the device produced treated water at an average rate of 143 mL/min (8.6 L/hour) (range 293 to 80 mL/min) over the course of the evaluation. If these results are validated in field trials, the deployment of the unit on a wide scale among vulnerable populations may make an important contribution to public health efforts to control intractable waterborne diseases. Copyright © 2009 by The American Society of Tropical Medicine and Hygiene.
• Gerba, C. P. (2009). Disinfection. Environmental Microbiology, 539-552.
• Gerba, C. P. (2009). Drinking Water Treatment. Environmental Microbiology, 531-538.
• Gerba, C. P. (2009). Environmentally Transmitted Pathogens. Environmental Microbiology, 445-484.
• Gerba, C. P. (2009). Indicator Microorganisms. Environmental Microbiology, 485-499.
• Gerba, C. P. (2009). Risk Assessment. Environmental Microbiology, 575-587.
• Gerba, C. P. (2009). The Role of Water and Water Testing in Produce Safety. Microbial Safety of Fresh Produce, 129-142.
• Gerba, C. P., & Choi, C. Y. (2009). Water Quality. The Produce Contamination Problem, 105-118.
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  Abstract: Water has always played a key role as a vehicle for the transmission of pathogens transmitted by the fecal-oral route. Several produce outbreaks have been known or suspected to have arisen from contamination in the field, suggesting contamination by irrigation or during handling. The microbial quality of irrigation water depends on the source of the water and contamination as it is transmitted through the distribution system. Contamination of produce may also occur through the use of contaminated water to apply pesticides, fertilizers, washing, hydrocooling, handwashing, and icing. It has been observed that use of contaminated hand wash water, resulting from multiple use by different individuals, can result in hand contamination by enteric bacteria. Furthermore, use of fecally contaminated water for application of pesticides or in wash water may lead to produce contamination. Although the percentage of pathogen transfer from contaminated water to produce by some types of irrigation methods (e.g., drip irrigation) may be low, risks can still be considered significant because of the low numbers of some enteric pathogens, such as viruses, necessary to cause infection. Meaningful standards for indicator bacteria that better assess the risk of produce contamination and risk of infection to the consumer need to be developed. © 2009 Elsevier Inc. All rights reserved.
• Gerba, C. P., Blair, B. L., Sarkar, P., Bright, K. R., MacLean, R. C., & Marciano-Cabral, F. (2009). Occurrence and control of Naegleria fowleri in drinking water wells. Giardia and Cryptosporidium: From Molecules to Diseases, 238-247.
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  Abstract: Naegleria fowleri is a water-based protozoan found naturally in soil and warm waters. The deaths of two children due to N. fowleri in the Phoenix, Arizona, metropolitan area occurred in 2002, and the drinking water obtained from groundwater was found to be the source of the exposure. A survey was conducted of municipal drinking water wells in central and southern Arizona. N. fowleri was identified in 11 of 143 wells tested. The calculated Ct (chlorine concentration × time) for N. fowleri cysts by free chlorine was 31 for a 99% reduction at room temperature, pH 7.5 and trophozoites 6. Chlorination can be used to control N. fowleri transmission via drinking water with appropriate guidance related to proper dosages and contact times. © CAB International 2009. Giardia and Cryptosporidium: From Molecules to Disease.
• Gerba, C. P., Gundy, P. M., Sicairos-Ruelas, E. E., & Bright, K. R. (2009). Assessment of the Antiviral Properties of Zeolites Containing Metal Ions. FOOD AND ENVIRONMENTAL VIROLOGY, 1(1), 37-41. doi:https://doi.org/10.1007/s12560-008-9006-1
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  The antiviral properties of zeolite (sodium aluminosilicate) powders amended with metal ions were assessed using human coronavirus 229E, feline infectious peritonitis virus (FIPV), and feline calicivirus F-9. Zeolites containing silver and silver/copper caused significant reductions of coronavirus 229E after 1 h in suspension. The silver/copper combination yielded a >5.13-log10 reduction within 24 h. It was also the most effective (>3.18-log10) against FIPV after 4 h. Other formulations were ineffective against FIPV. On plastic coupons with incorporated silver/copper-zeolites, >1.7-log10 and >3.8-log10 reductions were achieved for coronavirus 229E and feline calicivirus within 24 h, respectively. Silver/copper zeolite reduced titers of all viruses tested, suggesting that it may be effective against related pathogens of interest [i.e., SARS coronavirus, other coronaviruses, human norovirus (calicivirus)]. Of note, it was effective against both enveloped and nonenveloped viruses. Metal-zeolites could therefore possibly be used in applications to reduce virus contamination of fomites and thus the spread of viral diseases.
• Gerba, C. P., Marciano-Cabral, F., & Bright, K. R. (2009). Occurrence of Naegleria fowleri in Arizona drinking water supply wells. JOURNAL - AMERICAN WATER WORKS ASSOCIATION, 101(11), 43-50. doi:https://doi.org/10.1002/j.1551-8833.2009.tb09989.x
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  Naegleria fowleri is a protozoan found naturally in hot springs and warm surface waters. It can cause usually lethal primary amoebic meningoencephalitis. The goal of this study was to determine the occurrence of N. fowleri in drinking water supply wells in Arizona. Nested polymerase chain reaction was used to detect trophozoites and cysts, but not to assess viability. A total of 185 samples were collected from 113 wells before disinfection. The presence of N. fowleri deoxyribonucleic acid was confirmed in 10.6% of wells. No correlations were found between the presence of N. fowleri and heterotrophic bacteria, coliforms, Escherichia coli, temperature, specific conductance, or turbidity. N. fowleri was detected in 10.0% of initial and 17.2% of purged well samples, suggesting that N. fowleri may be present in the aquifer or detach from the well casing or pump column during pumping.
• Gerba, C., Black, S., Thurston, J. A., & Gerba, C. P. (2009). Determination of Ct values for chlorine of resistant enteroviruses. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 44(4).
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  Information on the required chlorine dose or Ct value (concentration of free chlorine multiplied by contact time) is limited to only a few enteroviruses. In this study the Ct values of some of the reported more chlorine resistant enteroviruses were determined. The Efficiency Hom Model was used to predict the times for 2, 3. and 4 -log inactivation of echovirus 1 and 12, coxsackievirus B5 and poliovirus type 1 at pH 7.5 and 9 at 5 degrees C. Coxsackievirus B5 was the most resistant to chlorine with a Ct requirement of 11.5 mg x min/L at pH 7.5 at 5 degrees C compared to polio with a Ct of 5.3 mg x min/L under the same conditions. All the viruses were more resistant than polio 1 at pH 9.0.
• Gerba, C., Jones, E. L., Gaither, M., Kramer, A., & Gerba, C. P. (2009). An analysis of water quality in the Colorado River, 2003-04; an investigation into recurring outbreaks of norovirus among rafters. Wilderness & environmental medicine, 20(1).
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  Every year over 22 000 people raft the Colorado River through the Grand Canyon in Arizona. Since 1994, over 400 rafters in 6 separate outbreaks have become ill with norovirus while rafting this stretch of the river.
• Gerba, C., Rodríguez, R. A., Pepper, I. L., & Gerba, C. P. (2009). Application of PCR-based methods to assess the infectivity of enteric viruses in environmental samples. Applied and environmental microbiology, 75(2).
• Gerba, C., Sinclair, R. G., Romero-Gomez, P., Choi, C. Y., & Gerba, C. P. (2009). Assessment of MS-2 phage and salt tracers to characterize axial dispersion in water distribution systems. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 44(10).
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  The present study investigates the axial dispersion and retardation patterns of viruses in a pressurized water distribution pipe using MS-2 as a surrogate. The results were obtained by using computational fluid dynamics (CFD), along with a hydraulic and water quality model. These models included the plug flow assumption and were first used to estimate transport mechanisms along a pipe. These prediction-model results were compared to experimental data using sodium chloride as a chemical tracer. Significant axial dispersion and retardation (or tailing) was found to exist under laminar flow conditions with high dispersion coefficients (E) estimated by CFD runs and salt tracer experiments. A similar dispersion pattern was also observed for MS-2, along with a long tailing pattern, which is particularly unique. The commonly used water quality model showed no axial dispersion (E = 0) under any flow regimes; thus, the plug flow assumption could produce significant errors in predicting the transport phenomena of chemical and biological constituents in water distribution systems. On the other hand, the dispersion curves predicted by the plug flow model and CFD are in good agreement with the experimental data in the turbulent flow regime, although using computational methods to predict microbial retardation is intrinsically difficult. Because the MS-2 demonstrated considerable temporal retardation and because its detection limit is much lower than that of the salt tracer, MS-2 should make an excellent tracer for characterizing viral transport in water distribution systems.
• Herzog, A. B., McLennan, S. D., Pandey, A. K., Gerba, C. P., Haas, C. N., Rose, J. B., & Hashsham, S. A. (2009). Implications of limits of detection of various methods for Bacillus anthracis in computing risks to human health. Applied and Environmental Microbiology, 75(19), 6331-6339.
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  PMID: 19648357;PMCID: PMC2753060;Abstract: Used for decades for biological warfare, Bacillus anthracis (category A agent) has proven to be highly stable and lethal. Quantitative risk assessment modeling requires descriptive statistics of the limit of detection to assist in defining the exposure. Furthermore, the sensitivities of various detection methods in environmental matrices are vital information for first responders. A literature review of peer-reviewed journal articles related to methods for detection of B. anthracis was undertaken. Articles focused on the development or evaluation of various detection approaches, such as PCR, real-time PCR, immunoassay, etc. Real-time PCR and PCR were the most sensitive methods for the detection of B. anthracis, with median instrument limits of detection of 430 and 440 cells/ml, respectively. There were very few peer-reviewed articles on the detection methods for B. anthracis in the environment. The most sensitive limits of detection for the environmental samples were 0.1 CFU/g for soil using PCR-enzyme-linked immunosorbent assay (ELISA), 17 CFU/liter for air using an ELISA-biochip system, 1 CFU/liter for water using cultivation, and 1 CFU/cm 2 for stainless steel fomites using cultivation. An exponential dose-response model for the inhalation of B. anthracis estimates of risk at concentrations equal to the environmental limit of detection determined the probability of death if untreated to be as high as 0.520. Though more data on the environmental limit of detection would improve the assumptions made for the risk assessment, this study's quantification of the risk posed by current limitations in the knowledge of detection methods should be considered when employing those methods in environmental monitoring and cleanup strategies. Copyright © 2009, American Society for Microbiology. All Rights Reserved.
• Jones, E. L., Gaither, M., Kramer, A., & Gerba, C. P. (2009). An analysis of water quality in the colorado river, 2003-04; An investigation into recurring outbreaks of norovirus among rafters. Wilderness and Environmental Medicine, 20(1), 6-13.
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  PMID: 19364162;Abstract: Background-Every year over 22 000 people raft the Colorado River through the Grand Canyon in Arizona. Since 1994, over 400 rafters in 6 separate outbreaks have become ill with norovirus while rafting this stretch of the river. Objectives-To assess potential causes of these outbreaks, Colorado River water, water from near by wastewater treatment plants, and a drinking water source were sampled and tested for norovirus and other water quality indicators. Methods-Colorado River water was collected and sampled during the 2004 rafting season. Water from wastewater treatment plants near the Lee's Ferry launch site and drinking water from the Lee's Ferry launch site were also examined during the 2003 and 2004 rafting seasons. Stool samples from ill rafters and composite stool samples from onboard toilet-cans were tested for the presence of norovirus during the 2003 and 2004 outbreaks. Parameters examined included the following: norovirus by reverse transcriptase-polymerase chain reaction, coliforms, Escherichia coli, temperature, turbidity, and pH. Results.-No norovirus was detected in the Colorado River during the 2004 field sampling. Norovirus was detected in the Glen Canyon Dam Wastewater Treatment Plant on one occasion in 2004. Drinking water from the Lee's Ferry launch site was negative for norovirus in 2003, and Colorado River water from the Lee's Ferry launch site was negative for norovirus in 2004. In 2003, 3 of 10 stool samples from ill rafters or onboard toilet-cans were positive for norovirus. Neither of 2 stool samples collected in 2004 was positive for norovirus. Conclusions-Colorado River water tested during nonoutbreak periods was negative for norovirus, indicating that there is not an ongoing high level of norovirus contamination in the river. No source or sources of contamination could be identified from the testing. Potential sources of norovirus outbreaks among rafters include drinking contaminated river water, consuming contaminated foodstuff, rafter importation of the virus and subsequent person-to-person spread, and contaminated fomites, campsites, or equipment. It is likely outbreaks are the result of more than one source of norovirus, and the exact source remains unknown for several outbreaks.
• Kim, M., Boone, S. A., & Gerba, C. P. (2009). Factors that influence the transport of Bacillus cereus spores through sand. Water, Air, and Soil Pollution, 199(1-4), 151-157.
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  Abstract: The goal of this study is to clarify the surface-chemical and microphysical variables that influence bacterial spore transport through soil, thereby defining the factors that may affect spore transport velocity. Bacillus cereus spores were continuously monitored in a soil column under saturated conditions with experimental variations in soil grain size (0.359 and 0.718 mm), pH (7.2 and 8.5), and water flow rate (1.3 and 3.0 mL/min). Increasing soil grain size, flow rate, and pH resulted in enhanced spore movement. Spore transport increased 82% when soil grain size was doubled. An increase in effluent flow rate from 1.3 to 3.0 mL/min increased spore movement by 71%. An increase in pH increased spore transport by 53%. The increase in hydrodynamic forces resulting from the larger grain size soil and higher flow rate functioned to overcome the hydrophobic nature of the spore's coat, and the interparticle bonding forces between the spore and soil particles. © 2008 Springer Science+Business Media B.V.
• L., S., Echevarría-Núñez, L., Riley, K., & Gerba, C. P. (2009). Assessment of disinfectant performance in chicken cages using coliphages. Food and Environmental Virology, 1(3), 155-160.
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  Abstract: To control the spread of avian flu (influenza) and other viruses of concern among commercial flocks, it is essential that proper disinfection procedures be developed along with methods for assessing their performance. Such methods must be rapid and inexpensive. Coliphages were used as indicators to demonstrate the efficacy of quaternary ammonium compounds and chlorine bleach for the inactivation of viruses in chicken cages. The concentration of indigenous coliphages in chicken litter was found to be 104-107 per gram and from 0 to 8,500 per 100 cm2 of floor surface. To assess the effectiveness of the disinfectants, floor samples were collected pre and post disinfection. These results indicated that chlorine bleach was more effective than quaternary ammonium compounds in reducing the amount of indigenous coliphages. To obtain better quantitative data, MS-2 coliphage was sprayed onto cage floors, left overnight to dry, and then the surfaces disinfected. Similar results were obtained with both indigenous coliphages and MS-2. There appears to be no significant difference in coliphage reduction by increasing the contact time from 10 to 30 min. To ensure at least a 99.9% reduction of virus at least 236 ml of household bleach per 3.78 l should be used. © The Visualization Society of Japan 2009.
• Malek, M., Barzilay, E., Kramer, A., Camp, B., Jaykus, L., Escudero-Abarca, B., Derrick, G., White, P., Gerba, C., Higgins, C., Vinje, J., Glass, R., Lynch, M., & Widdowson, M. (2009). Outbreak of norovirus infection among river rafters associated with packaged delicatessen meat, Grand Canyon, 2005. Clinical Infectious Diseases, 48(1), 31-37.
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  PMID: 19025489;Abstract: Background. Norovirus is often transmitted by infected food handlers at the point of service, whereas reports of food contamination before wholesale distribution are rare. In September 2005, we investigated reports of gastroenteritis among rafters who went on unrelated trips on the Colorado River. Methods. We surveyed all companies that launched rafting trips during the period from 14 August through 19 September 2005 to identify trips in which ≥3 rafters became ill. We conducted a case-control study. Case patients were persons who experienced diarrhea or vomiting that commenced ≤72 h after the trip launch; control subjects were persons who did not become ill ≤72 h after launch. We tested stool samples and food specimens for norovirus. We performed a traceback investigation of the suspected food vehicle and inspected the implicated processing plant. Results. Three or more rafters developed gastroenteritis during 13 (14%) of 91 trips, for a total of 137 ill persons. Of the 57 case patients who became ill ≤72 h after trip launch, 55 (96%) reported eating delicatessen meat, compared with 75 (79%) of 95 control subjects (odds ratio, 7.3; 95% confidence interval, 1.7-66.7). All delicatessen meat eaten by case patients came from 1 batch purchased from 1 processing plant and had been sliced, vacuum-packed, and frozen (temperature, -23°C) for 7-28 days. An employee sliced this batch with bare hands 1 day after recovery from gastroenteritis. Identical norovirus sequences were identified in stool specimens obtained from rafters on 3 different trips; 2 of 5 meat packages also tested positive for norovirus by reverse-transcriptase polymerase chain reaction and DNA hybridization. Conclusions. Food handlers can contaminate ready-to-eat meats with norovirus during processing. Meatprocessing practices should include specific measures to prevent contamination with enteric viruses and subsequent widespread outbreaks. © 2008 by the Infectious Diseases Society of America. All rights reserved.
• Marero-Ortiz, R., Riley, K. R., Karpiscak, M. K., & Gerba, C. P. (2009). Groundwater quality of individual wells and small systems in Arizona. Journal / American Water Works Association, 101(9), 89-100+16.
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  Abstract: Approximately half of the waterborne disease outbreaks documented annually in the United States are caused by contaminated groundwater. In 2006, the US Environmental Protection Agency promulgated the final Ground Water Rule to reduce the risk of exposure to fecal contamination that may be present in community and noncommunity public groundwater systems. In most states, private drinking water systems are not regulated by local health and environmental agencies. The goal of the study presented in this article was to assess the microbial, physical, and chemical quality of groundwater in individual wells and small public water systems in Arizona, and it was the first such study in an arid region of the United States. Of the well sites sampled, 43% of the systems were positive for total coliforms, 16% for fecal coliforms, and 4% for Escherichia coli. In addition, 95% of systems exceeded at least one primary and/or secondary drinking water standard, suggesting that better guidance is needed to ensure the water quality of these systems.-NLP.
• Mena, K. D., & Gerba, C. P. (2009). Risk assessment of pseudomonas aeruginosa in water. Reviews of Environmental Contamination and Toxicology, 201, 71-115.
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  PMID: 19484589;Abstract: Pseudomonads are a large group of free-living bacteria that live primarily in soil, seawater, and fresh water. They also colonize plants and animals, and are frequently found in home and clinical settings. Pseudomonads are highly versatile and can adapt to a wide range of habitats, and can even grow in distilled water. This adaptability accounts for their constant presence in the environment. They have an extensive impact on ecology, agriculture, and commerce. They are responsible for food spoilage and degradation of petroleum products and materials. In agriculture, pseudomonads rank among the most important plant pathogens. In normal healthy humans, they are responsible for eye and skin diseases. They also cause serious life-threatening illnesses in burn and surgical patients and in immunocompromised individuals. Contamination of recreational waters and tap water has been associated with outbreaks of Pseudomonas; however, the relative role water plays in the transmission of this bacterium to humans is still unclear. The goal of this review is to assess existing literature on the potential risks associated with waterborne Pseudomonas aeruginosa. © 2009 Springer-Verlag US.
• Mena, K. D., & Gerba, C. P. (2009). Waterborne adenovirus. Reviews of Environmental Contamination and Toxicology, 198, 133-167.
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  PMID: 19253037;Abstract: Adenoviruses are associated with numerous disease outbreaks, particularly those involving d-cares, schools, children's camps, hospitals and other health care centers, and military settings. In addition, adenoviruses have been responsible for many recreational water outbreaks, including a greater number of swimming pool outbreaks than any other waterborne virus (Gerba and Enriquez 1997). Two drinking water outbreaks have been documented for adenovirus (Divizia et al. 2004; Kukkula et al. 1997) but none for food. Of the 51 known adenovirus serotypes, one third are associated with human disease, while other infections are asymptomatic. Human diseases associated with adenovirus infections include gastroenteritis, respiratory infections, eye infections, acute hemorrhagic cystitis, and meningoencephalitis (Table 2). Children and the immunocompromised are more severely impacted by adenovirus infections. Subsequently, adenovirus is included in the EPA's Drinking Water Contaminant Candidate List (CCL), which is a list of unregulated contaminants found in public water systems that may pose a risk to public health (National Research Council 1999). Adenoviruses have been detected in various waters worldwide including wastewater, river water, oceans, and swimming pools (Hurst et al. 1988; Irving and Smith 1981; Pina et al. 1998). Adenoviruses typically outnumber the enteroviruses, when both are detected in surface waters. Chapron et al. (2000) found that 38% of 29 surface water samples were positive for infectious Ad40 and Ad41. Data are lacking, Waterborne Adenovirus 159 regarding the occurrence of adenovirus in water in the US, particularly for groundwater and drinking water. Studies have shown, however, that adenoviruses survive longer in water than enteroviruses and hepatitis A virus (Enriquez et al. 1995), which may be due to their double-stranded DNA. Risk assessments have been conducted on waterborne adenovirus (Crabtree et al. 1997; van Heerden et al. 2005c). Using dose-response data for inhalation from Couch et al. (1966), human health risks of infection, illness and death have been determined for various adenovirus exposures. Crabtree et al. (1997) conclude that, even at an adenovirus concentration of 1 per 1,000 L of drinking water, annual risks of infection exceed the suggested risk recommendation of 1 × 10-4 per yr (Regli et al. 1991) (Table 8). Using the same exposure and dose-response assumptions, van Heerden et al. (2005c) determined annual risks of infection to be 1-1.7 × 10-1 for two drinking water samples from South Africa containing 1.40 and 2.45 adenoviruses per 10,000 L, respectively. This present study estimated annual risks of infection associated with varying levels of adenoviruses per 100 L (Table 9). By assuming a 2 L/d exposure and utilizing the exponential model at r = 0.4172 (Haas et al. 1993), yearly risks exceed the risk recommendation of 1 × 10-4 at every exposure level. There are limited data regarding the removal of adenoviruses by conventional water treatment or other physical-chemical treatment processes, but studies do suggest that adenoviruses are of equal or greater sensitivity to oxidizing disinfectants, when compared to other waterborne viruses (the most resistant to ultraviolet light). Data suggest that the chlorine doses applied to control other waterborne viruses are more effective against adenovirus, resulting in a greater than 4-log10 removal of adenoviruses by conventional treatment and chlorination. If treatment can achieve a 4-log10 removal of adenoviruses, then, based on the risk levels presented in Table 9, surface water concentrations should not exceed 0.5 adenoviruses per 100 L (Fig. 2). More data are needed regarding the occurrence of adenovirus in groundwater and drinking water, the effectiveness of water treatment against adenovirus, and the human-virus dose-response relationship to fully understand the role of adenovirus as a waterborne public health threat. © Springer Science + Business Media, LLC 2008.
• Rijal, G., Petropoulou, C., Tolson, J. K., DeFlaun, M., Gerba, C., Gore, R., Glymph, T., Granato, T., O'Connor, C., Kollias, L., & Lanyon, R. (2009). Dry and wet weather microbial characterization of the Chicago area waterway system. Water Science and Technology, 60(7), 1847-1855.
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  PMID: 19809148;Abstract: The Chicago Area Waterway System (CAWS) is a man-made channel, which serves the Chicago area for the drainage of urban storm water and the conveyance of secondary treated effluent from the Metropolitan Water Reclamation District of Greater Chicago's (District) North Side, Stickney and Calumet water reclamation plants (WRPs). A microbial characterization of the CAWS upstream and downstream of the WRPs and from the WRP outfall was initiated by collecting dry and wet weather samples and analyzing for indicators and pathogens. During dry weather, indicator bacteria (fecal coliform [FC], E. coli [EC], enterococci [EN]) were the most abundant microbial species detected in the CAWS compared to pathogens (Salmonella spp [SA], enteric viruses [EV], adenovirus [AV], norovirus [NV] and Giardia and Cryptosporidium). Pseudomonas aeruginosa [PA] levels in the outfall samples were either lower or equivalent to the CAWS. The wet weather samples had a higher frequency of detection of indicator bacteria and pathogens compared to dry weather samples. Overall, the concentrations of pathogens in the CAWS, representing the weather conditions experienced in a recreational year, were relatively low. The study concluded that the presence of pathogens in the CAWS downstream of the WRPs were due to secondary loading of the waterway under wet weather conditions from combined sewer overflows (CSOs) and other discharges. © IWA Publishing 2009.
• Sinclair, R. G., Jones, E. L., & Gerba, C. P. (2009). Viruses in recreational water-borne disease outbreaks: A review. Journal of Applied Microbiology, 107(6), 1769-1780.
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  PMID: 19486213;Abstract: Viruses are believed to be a significant cause of recreationally associated water-borne disease. However, they have been difficult to document because of the wide variety of illnesses that they cause and the limitations in previous detection methods. Noroviruses are believed to be the single largest cause of outbreaks, which have been documented in the published literature 45% (n = 25), followed by adenovirus (24%), echovirus (18%), hepatitis A virus (7%) and coxsackieviruses (5%). Just under half of the outbreaks occurred in swimming pools (49%), while the second largest outbreak occurred in lakes or ponds (40%). The number of reported outbreaks associated with noroviruses has increased significantly in recent years probably because of better methods for virus detection. Inadequate disinfection was related to 69% (n = 18) of swimming pool outbreaks. A lack of required reporting and nonuniform water quality and chlorination/disinfection standards continues to contribute to water-borne recreational disease outbreaks. © 2009 The Society for Applied Microbiology.
• Sinclair, R. G., Romero-Gomez, P., Choi, C. Y., & Gerba, C. P. (2009). Assessment of MS-2 phage and salt tracers to characterize axial dispersion in water distribution systems. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 44(10), 963-971.
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  PMID: 19827488;Abstract: The present study investigates the axial dispersion and retardation patterns of viruses in a pressurized water distribution pipe using MS-2 as a surrogate. The results were obtained by using computational fluid dynamics (CFD), along with a hydraulic and water quality model. These models included the plug flow assumption and were first used to estimate transport mechanisms along a pipe. These prediction-model results were compared to experimental data using sodium chloride as a chemical tracer. Significant axial dispersion and retardation (or tailing) was found to exist under laminar flow conditions with high dispersion coefficients (E) estimated by CFD runs and salt tracer experiments. A similar dispersion pattern was also observed for MS-2, along with a long tailing pattern, which is particularly unique. The commonly used water quality model showed no axial dispersion (E = 0) under any flow regimes; thus, the plug flow assumption could produce significant errors in predicting the transport phenomena of chemical and biological constituents in water distribution systems. On the other hand, the dispersion curves predicted by the plug flow model and CFD are in good agreement with the experimental data in the turbulent flow regime, although using computational methods to predict microbial retardation is intrinsically difficult. Because the MS-2 demonstrated considerable temporal retardation and because its detection limit is much lower than that of the salt tracer, MS-2 should make an excellent tracer for characterizing viral transport in water distribution systems.
• Ángel, M., Bright, K. R., & Gerba, C. P. (2009). Clostridium difficile hospital infection control. Enfermedades Infecciosas y Microbiologia, 29(3), 117-118.
• Blair, B., Sarkar, P., Bright, K. R., Marciano-Cabral, F., & Gerba, C. P. (2008). Naegleria fowleri in well water. Emerging Infectious Diseases, 14(9), 1499-1501.
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  PMID: 18760036;PMCID: PMC2603111;
• Gerba, C. P., & Rodriguez, R. A. (2008). Adenoviruses. International Encyclopedia of Public Health, 28-33.
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  Abstract: The human adenoviruses consist of 51 serotypes. They cause a wide variety of illnesses including upper respiratory tract infections, conjunctivitis (eye infection), bladder infections, pneumonia, encephalitis, and gastroenteritis. They have also been implicated in heart disease and obesity. Adenovirus infections can be devastating among the immunocompromised (organ transplant, cancer, and AIDS patients), resulting in high mortality rates. Recreational water outbreaks of adenoviruses have been associated with eye, throat, and respiratory infections from pools that lack adequate levels of disinfection. Adenoviruses have been isolated from wastewater, rivers, and drinking water and are capable of prolonged survival in water. © 2008 Copyright © 2008 Elsevier Inc. All rights reserved.
• Gerba, C. P., Marciano-Cabral, F., Bright, K. R., Sarkar, P., & Blair, B. (2008). Naegleria fowleri in well water. EMERGING INFECTIOUS DISEASES, 14(9), 1499-1501. doi:https://doi.org/10.3201/eid1409.071076
• Gerba, C. P., Naranjo, J. E., & Jones, E. L. (2008). Virus removal from water by a portable water treatment device. Wilderness and Environmental Medicine, 19(1), 45-49.
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  PMID: 18333657;Abstract: Objective. - Few portable point-of-use (POU) devices are available for treatment of water by recreational enthusiasts who may obtain water from untreated sources (rivers, lakes, etc.). This study evaluated a POU device containing a structure matrix capable of removing viruses from water without the use of a disinfectant. Methods. - The unit was evaluated for the removal of poliovirus type 1, rotavirus SA-11, human norovirus, and a wide range of different coliphages exhibiting different isoelectric points, sizes, and shapes. Results. - The removal of all virus types tested exceeded 99.99%. Conclusion. - The tested unit complied with the criteria guidelines for virus removal under the US Environmental Protection Agency's "Guide Standard and Protocol for Testing of Microbiological Water Purifiers".
• Gerba, C., Karim, M. R., Glenn, E. P., & Gerba, C. P. (2008). The effect of wetland vegetation on the survival of Escherichia coli, Salmonella typhimurium, bacteriophage MS-2 and polio virus. Journal of water and health, 6(2).
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  A study was conducted to examine the role of aquatic plants used in constructed wetlands on the survival of enteric bacteria and viruses. Four small-scale wetland systems, receiving fresh water and two other wetland systems, receiving secondary unchlorinated sewage were used in this study. Fresh water and secondary sewage without the presence of any aquatic plants were used as controls. Escherichia coli, Salmonella typhimurium, bacteriophage MS-2 and poliovirus were added to the waters collected from the wetlands and controls. The presence of aquatic plants significantly increased the die-off of both bacteria in fresh water and secondary sewage. No significant difference in the die-off of E. coli and S. typhimurium was observed in water from wetlands with different types of plants in freshwater. However, there was a significant difference in the die-off of E. coli in water with aquatic plants when sewage was used. The presence of the plants significantly increased the inactivation of MS-2 and poliovirus. Additional work on the survival of E. coli indicated that the plausible mechanism of bacterial die-off in constructed wetlands is through increased microbial competition or predation.
• Gerba, C., Reynolds, K. A., Mena, K. D., & Gerba, C. P. (2008). Risk of waterborne illness via drinking water in the United States. Reviews of environmental contamination and toxicology, 192.
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  Outbreaks of disease attributable to drinking water are not common in the U.S., but they do still occur and can lead to serious acute, chronic, or sometimes fatal health consequences, particularly in sensitive and immunocompromised populations. From 1971 to 2002, there were 764 documented waterborne outbreaks associated with drinking water, resulting in 575,457 cases of illness and 79 deaths (Blackburn et al. 2004; Calderon 2004); however, the true impact of disease is estimated to be much higher. If properly applied, current protocols in municipal water treatment are effective at eliminating pathogens from water. However, inadequate, interrupted, or intermittent treatment has repeatedly been associated with waterborne disease outbreaks. Contamination is not evenly distributed but rather affected by the number of pathogens in the source water, the age of the distribution system, the quality of the delivered water, and climatic events that can tax treatment plant operations. Private water supplies are not regulated by the USEPA and are generally not treated or monitored, although very few of the municipal systems involved in documented outbreaks exceeded the USEPA's total coliform standard in the preceding 12 mon (Craun et al. 2002). We provide here estimates of waterborne infection and illness risks in the U.S. based on the total number of water systems, source water type, and total populations exposed. Furthermore, we evaluated all possible illnesses associated with the microbial infection and not just gastroenteritis. Our results indicate that 10.7 M infections/yr and 5.4 M illnesses/yr occur in populations served by community groundwater systems; 2.2 M infections/yr and 1.1 M illnesses/yr occur in noncommunity groundwater systems; and 26.0 M infections/yr and 13.0 M illnesses/yr occur in municipal surface water systems. The total estimated number of waterborne illnesses/yr in the U.S. is therefore estimated to be 19.5 M/yr. Others have recently estimated waterborne illness rates of 12M cases/yr (Colford et al. 2006) and 16 M cases/yr (Messner et al. 2006), yet our estimate considers all health outcomes associated with exposure to pathogens in drinking water rather than only gastrointestinal illness. Drinking water outbreaks exemplify known breaches in municipal water treatment and distribution processes and the failure of regulatory requirements to ensure water that is free of human pathogens. Water purification technologies applied at the point-of-use (POU) can be effective for limiting the effects of source water contamination, treatment plant inadequacies, minor intrusions in the distribution system, or deliberate posttreatment acts (i.e., bioterrorism). Epidemiological studies are conflicting on the benefits of POU water treatment. One prospective intervention study found that consumers of reverse-osmosis (POU) filtered water had 20%-35% less gastrointestinal illnesses than those consuming regular tap water, with an excess of 14% of illness due to contaminants introduced in the distribution system (Payment 1991, 1997). Two other studies using randomized, blinded, controlled trials determined that the risks were equal among groups supplied with POU-treated water compared to untreated tap water (Hellard et al. 2001; Colford et al. 2003). For immunocompromised populations, POU water treatment devices are recommended by the CDC and USEPA as one treatment option for reducing risks of Cryptosporidium and other types of infectious agents transmitted by drinking water. Other populations, including those experiencing "normal" life stages such as pregnancy, or those very young or very old, might also benefit from the utilization of additional water treatment options beyond the current multibarrier approach of municipal water treatment.
• Gerba, C., Rodríguez, R. A., Gundy, P. M., & Gerba, C. P. (2008). Comparison of BGM and PLC/PRC/5 cell lines for total culturable viral assay of treated sewage. Applied and environmental microbiology, 74(9).
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  The objective of this study was to compare PLC/PRF/5 and BGM cell lines for use in a total culturable viral assay (TCVA) of treated sewage effluents. Samples were collected before and after chlorination from an activated sludge wastewater treatment plant and from the effluent of a high-rate enhanced flocculation system, followed by UV light disinfection. Cell monolayers were observed for cytopathic effect (CPE) after two passages of 14 days each. Monolayers exhibiting viral CPE were tested for the presence of adenoviruses and enteroviruses by PCR or reverse transcription-PCR. Eight percent of the samples exhibited CPE on BGM cells, and 57% showed CPE on PLC/PRF/5 cells. Only enteroviruses were detected on the BGM cells, while 30% and 52% of the samples were positive for enteroviruses and adenoviruses, respectively, on the PLC/PRF/5 cells. Thirty percent of the samples were positive for both adenoviruses and enteroviruses in chlorinated activated sludge effluent. Thirty percent of the samples were positive for adenoviruses in the UV treatment effluent, but no enteroviruses were detected. In conclusion, the PLC/PRF/5 cells were more susceptible than BGM cells to viruses found in treated sewage. The use of BGM cells for TCVA may underestimate viral concentration in sewage effluent samples. The PLC/PRF/5 cells were more susceptible to adenoviruses, which is important in the evaluation of UV disinfection systems because adenoviruses are highly resistant to UV inactivation.
• Gerba, C., Silvestry-Rodriguez, N., Bright, K. R., Slack, D. C., Uhlmann, D. R., & Gerba, C. P. (2008). Silver as a residual disinfectant to prevent biofilm formation in water distribution systems. Applied and environmental microbiology, 74(5).
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  Biofilms can have deleterious effects on drinking water quality and may harbor pathogens. Experiments were conducted using 100 microg/liter silver to prevent biofilm formation in modified Robbins devices with polyvinyl chloride and stainless steel surfaces. No significant difference was observed on either surface between the silver treatment and the control.
• Gerba, C., Sinclair, R. G., Choi, C. Y., Riley, M. R., & Gerba, C. P. (2008). Pathogen surveillance through monitoring of sewer systems. Advances in applied microbiology, 65.
• Gerba, C., Sinclair, R., Boone, S. A., Greenberg, D., Keim, P., & Gerba, C. P. (2008). Persistence of category A select agents in the environment. Applied and environmental microbiology, 74(3).
• Kim, M., Choi, C. Y., & Gerba, C. P. (2008). Source tracking of microbial intrusion in water systems using artificial neural networks. Water Research, 42(4-5), 1308-1314.
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  PMID: 17988708;Abstract: A "what-if" scenario where biological agents are accidentally or deliberately introduced into a water system was generated, and artificial neural network (ANN) models were applied to identify the pathogenic release location to isolate the contaminated area and minimize its hazards. The spatiotemporal distribution of Escherichia coli 15597 along the water system was employed to locate pollutants by inversely interpreting transport patterns of E. coli using ANNs. Results showed that dispersion patterns of E. coli were positively correlated to pH, turbidity, and conductivity (R2=0.90-0.96), and the ANN models successfully identified the source location of E. coli introduced into a given system with 75% accuracy based on the pre-programmed relationships between E. coli transport patterns and release locations. The findings in this study will enable us to assess the vulnerability of essential water systems, establish the early warning system and protect humans and the environment. © 2007.
• Mena, K. D., Rose, J. B., & Gerba, C. P. (2008). Addressing Microbial Food Safety Issues Quantitatively: A Risk Assessment Approach. Preharvest and Postharvest Food Safety: Contemporary Issues and Future Directions, 415-426.
• Nwachuku, N., & Gerba, C. P. (2008). Occurrence and persistence of Escherichia coli O157:H7 in water. Reviews in Environmental Science and Biotechnology, 7(3), 267-273.
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  Abstract: Escherichia coli O157:H7 has been associated with water related outbreaks. It has been isolated from surface and ground waters. It is capable of survival in water for days to weeks. © 2008 Springer Science+Business Media B.V.
• Reynolds, K. A., Mena, K. D., & Gerba, C. P. (2008). Risk of waterborne illness via drinking water in the United States. Reviews of Environmental Contamination and Toxicology, 192, 117-158.
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  PMID: 18020305;Abstract: The quality of drinking water in the United States is among the best in the world; however, waterborne disease outbreaks continue to occur, and many more cases of endemic illness are estimated. Documented waterborne disease outbreaks are primarily the result of technological failures or failure to treat the water (Craun et al. 2006). Current federal regulations require that all surface waters used for a drinking water supply be treated to reduce the level of pathogens so as to reduce the risk of infection to 1:10,000 per year (Regli et al. 1991). To achieve this goal, water treatment must, at a minimum, reduce infectious viruses by 99.99% and protozoan parasites by 99.9% (Regli et al. 2003). If Cryptosporidium concentrations exceed a certain level in the source water, additional reductions are required. This degree of treatment is usually achieved by a combination of physical processes (coagulation, sedimentation, and filtration) and disinfection (chlorination, ozonation). Filtration is essential for the removal of protozoan parasites due to their resistance to chlorination and ozonation at doses normally used in drinking water treatment (Barbeau et al. 2000; Korich et al. 1990; Rennecker et al. 1999). A variance from filtration is allowed in some cases if the watershed is protected and carefully monitored for protozoan pathogens. © 2008 Springer.
• Rodríguez, R. A., Gundy, P. M., & Gerba, C. P. (2008). Comparison of BGM and PLC/PRC/5 cell lines for total culturable viral assay of treated sewage. Applied and Environmental Microbiology, 74(9), 2583-2587.
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  PMID: 18326686;PMCID: PMC2394896;Abstract: The objective of this study was to compare PLC/PRF/5 and BGM cell lines for use in a total culturable viral assay (TCVA) of treated sewage effluents. Samples were collected before and after chlorination from an activated sludge wastewater treatment plant and from the effluent of a high-rate enhanced flocculation system, followed by UV light disinfection. Cell monolayers were observed for cytopathic effect (CPE) after two passages of 14 days each. Monolayers exhibiting viral CPE were tested for the presence of adenoviruses and enteroviruses by PCR or reverse transcription-PCR. Eight percent of the samples exhibited CPE on BGM cells, and 57% showed CPE on PLC/PRF/5 cells. Only enteroviruses were detected on the BGM cells, while 30% and 52% of the samples were positive for enteroviruses and adenoviruses, respectively, on the PLC/PRF/5 cells. Thirty percent of the samples were positive for both adenoviruses and enteroviruses in chlorinated activated sludge effluent. Thirty percent of the samples were positive for adenoviruses in the UV treatment effluent, but no enteroviruses were detected. In conclusion, the PLC/PRF/5 cells were more susceptible than BGM cells to viruses found in treated sewage. The use of BGM cells for TCVA may underestimate viral concentration in sewage effluent samples. The PLC/PRF/5 cells were more susceptible to adenoviruses, which is important in the evaluation of UV disinfection systems because adenoviruses are highly resistant to UV inactivation. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
• Sinclair, R. G., Choi, C. Y., Riley, M. R., & Gerba, C. P. (2008). Chapter 9 Pathogen Surveillance Through Monitoring of Sewer Systems. Advances in Applied Microbiology, 65, 249-269.
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  PMID: 19026868;
• Sinclair, R., Boone, S. A., Greenberg, D., Keim, P., & Gerba, C. P. (2008). Persistence of category A select agents in the environment. Applied and Environmental Microbiology, 74(3), 555-563.
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  PMID: 18065629;PMCID: PMC2227740;
• Boone, S. A., & Gerba, C. P. (2007). Significance of fomites in the spread of respiratory and enteric viral disease. Applied and Environmental Microbiology, 73(6), 1687-1696.
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  PMID: 17220247;PMCID: PMC1828811;
• Gerba, C. P. (2007). Chapter 5 Virus Occurrence and Survival in the Environmental Waters. Perspectives in Medical Virology, 17, 91-108.
• Gerba, C. P., & Kennedy, D. (2007). Enteric virus survival during household laundering and impact of disinfection with sodium hypochlorite. Applied and Environmental Microbiology, 73(14), 4425-4428.
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  PMID: 17526793;PMCID: PMC1932823;Abstract: This study was conducted to determine whether enteric viruses (adenovirus, rotavirus, and hepatitis A virus) added to cotton cloth swatches survive the wash cycle, the rinse cycle, and a 28-min permanent press drying cycle as commonly practiced in households in the United States. Detergent with and without bleach (sodium hypochlorite) was added to washing machines containing sterile and virus-inoculated 58-cm2 swatches, 3.2 kg of cotton T-shirts and underwear, and a soiled pillowcase designed to simulate the conditions (pH, organic load, etc.) encountered in soiled laundry. The most important factors for the reduction of virus in laundry were passage through the drying cycle and the addition of sodium hypochlorite. Washing with detergent alone was not found to be effective for the removal or inactivation of enteric viruses, as significant concentrations of virus were found on the swatches (reductions of 92 to 99%). It was also demonstrated that viruses are readily transferred from contaminated cloths to uncontaminated clothes. The use of sodium hypochlorite reduced the number of infectious viruses on the swatches after washing and drying by at least 99.99%. Laundering practices in common use in the United States do not eliminate enteric and respiratory viruses from clothes. The use of bleach can further reduce the numbers of enteric viruses in laundry. Copyright © 2007, American Society for Microbiology. All Rights Reserved.
• Gerba, C. P., Blair, B., Sarkar, P., & Bright, K. (2007). Occurrence and control of naegleria fowleri in well water chlorine resistance. American Water Works Association - Water Quality Technology Conference and Exposition 2007: Fast Tracks to Water Quality, 1582-1596.
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  Abstract: The goal of this project was to determine the occurrence of the N. fowleri in well water. The presence of Naegleria fowleri was confirmed in 8.3% of the wells sampled. Re-testing of a subset of wells suggests that some wells are colonized by the organism. Laboratory experiments with N. fowleri cysts and trophozoites indicate that the Ct (concentration of disinfectant X time) for free chlorine is 6 for the trophozoite form and 31 for the cysts at 23 0C. These Ct values for N. fowleri cysts were comparable to published values for Giardia cysts but much greater than those for Cryptosporidium oocysts. © 2007 American Water Works Association.
• Gerba, C., Boone, S. A., & Gerba, C. P. (2007). Significance of fomites in the spread of respiratory and enteric viral disease. Applied and environmental microbiology, 73(6).
• Gerba, C., Jones, E. L., Kramer, A., Gaither, M., & Gerba, C. P. (2007). Role of fomite contamination during an outbreak of norovirus on houseboats. International journal of environmental health research, 17(2).
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  An outbreak of suspected norovirus gastroenteritis among three consecutive groups of houseboaters on a large recreational lake in Arizona was investigated to assess the role of fomite contamination, and to provide recommendations for prevention of future outbreaks. Interior boat surfaces were sampled for norovirus using transport swabs. Onboard toilet reservoirs were swabbed as a surrogate for stool samples from ill participants, since none were available, and onboard potable water supplies were sampled for norovirus. All samples were analyzed using RT-PCR with primers specific for human norovirus. Widespread fomite contamination was documented in the houseboats; 83% (5/6) of bathroom surface samples, 40% (2/5) of kitchen surface samples, and 100% (3/3) of doorknob samples were positive for the presence of norovirus. Samples of onboard potable water supplies were all negative. One of the participants on the first boating trip arrived already displaying symptoms of gastrointestinal illness prior to boarding the boat. This investigation demonstrates the potential role of widespread fomite contamination in outbreaks in confined spaces. To prevent or minimize future outbreaks in confined spaces, the adoption of practices such as surface disinfection and the utilization of methods to identify and exclude those with gastroenteritis from trips or activities in confined spaces, where others may become infected, are recommended.
• Gerba, C., Silvestry-Rodriguez, N., Bright, K. R., Uhlmann, D. R., Slack, D. C., & Gerba, C. P. (2007). Inactivation of Pseudomonas aeruginosa and Aeromonas hydrophila by silver in tap water. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 42(11).
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  This study was conducted to assess the efficacy of silver as a secondary disinfectant to replace or reduce the level of chlorine utilized in water distribution systems. Pseudomonas aeruginosa and Aeromonas hydrophila are opportunistic pathogens present in drinking water and have been associated with waterborne disease. After 8 hours of exposure to 100 microg/L of silver, there was a >6-log10 reduction in P. aeruginosa in tap water at room temperature at pH7 and a 5.55-log10 reduction in the presence of 3 mg/L humic acid. Similar reductions were observed at pH9. At 4 degrees C, reductions greater than 4-log10 were observed after 24 hours. For A. hydrophila, a >6-log10 reduction occurred at both pH7 and pH9 within nine hours. The World Health Organization has determined that this amount of silver could be used for water disinfection without health risks. Furthermore, silver shows promise as a secondary disinfectant, even in the presence of organic matter in concentrations that would reduce the effectiveness of free chlorine.
• Jones, E. L., Kramer, A., Gaither, M., & Gerba, C. P. (2007). Role of fomite contamination during an outbreak of norovirus on houseboats. International Journal of Environmental Health Research, 17(2), 123-131.
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  PMID: 17616868;Abstract: An outbreak of suspected norovirus gastroenteritis among three consecutive groups of houseboaters on a large recreational lake in Arizona was investigated to assess the role of fomite contamination, and to provide recommendations for prevention of future outbreaks. Interior boat surfaces were sampled for norovirus using transport swabs. Onboard toilet reservoirs were swabbed as a surrogate for stool samples from ill participants, since none were available, and onboard potable water supplies were sampled for norovirus. All samples were analyzed using RT-PCR with primers specific for human norovirus. Widespread fomite contamination was documented in the houseboats; 83% (5/6) of bathroom surface samples, 40% (2/5) of kitchen surface samples, and 100% (3/3) of doorknob samples were positive for the presence of norovirus. Samples of onboard potable water supplies were all negative. One of the participants on the first boating trip arrived already displaying symptoms of gastrointestinal illness prior to boarding the boat. This investigation demonstrates the potential role of widespread fomite contamination in outbreaks in confined spaces. To prevent or minimize future outbreaks in confined spaces, the adoption of practices such as surface disinfection and the utilization of methods to identify and exclude those with gastroenteritis from trips or activities in confined spaces, where others may become infected, are recommended. © 2007 Taylor & Francis.
• Silvestry-Rodriguez, N., Sicairos-Ruelas, E. E., Gerba, C. P., & Bright, K. R. (2007). Silver as a disinfectant. Reviews of Environmental Contamination and Toxicology, 191, 23-45.
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  PMID: 17708071;Abstract: The antimicrobial effects of silver (Ag) have been recognized for thousands of years. In ancient times, it was used in water containers (Grier 1983) and to prevent putrefaction of liquids and foods. In ancient times in Mexico, water and milk were kept in silver containers (Davis and Etris 1997). Silver was also mentioned in the Roman pharmacopoeia of 69 b.c. (Davis and Etris 1997). © 2007 Springer.
• Straub, T. M., Höner, K., Orosz-Coghlan, P., Dohnalkova, A., Mayer, B. K., Bartholomew, R. A., Valdez, C. O., Bruckner-Lea, C. J., Gerba, C. P., Abbaszadegan, M. A., & Nickerson, C. A. (2007). In response [2]. Emerging Infectious Diseases, 13(7), 1117-1118.
• Straub, T. M., Höner, K., Orosz-Coghlan, P., Dohnalkova, A., Mayer, B. K., Bartholomew, R. A., Valdez, C. O., Bruckner-Lea, C. J., Gerba, C. P., Abbaszadegan, M., & Nickerson, C. A. (2007). In vitro cell culture infectivity assay for human noroviruses. Emerging Infectious Diseases, 13(3), 396-403.
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  PMID: 17552092;PMCID: PMC2725917;Abstract: Human noroviruses cause severe, self-limiting gastroenteritis that typically lasts 24-48 hours. Because of the lack of suitable tissue culture or animal models, the true nature of norovirus pathogenesis remains unknown. We show, for the first time, that noroviruses can infect and replicate in a physiologically relevant 3-dimensional (3-D), organoid model of human small intestinal epithelium. This level of cellular differentiation was achieved by growing the cells on porous collagen-I coated microcarrier beads under conditions of physiological fluid shear in rotating wall vessel bioreactors. Microscopy, PCR, and fluorescent in situ hybridization provided evidence of norovirus infection. Cytopathic effect and norovirus RNA were detected at each of the 5 cell passages for genogroup I and II viruses. Our results demonstrate that the highly differentiated 3-D cell culture model can support the natural growth of human noroviruses, whereas previous attempts that used differentiated monolayer cultures failed.
• Tamimi, A. H., Gerba, C. P., Hayek, B., Choi, C. Y., & Freitas, R. J. (2007). Characterization of the quality of drying bed treated biosolids in Jordan. Journal of Residuals Science and Technology, 4(3), 113-119.
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  Abstract: Disposal of liquid and dewatered sludge at storage sites and landfills is currently the most widely practiced method dealing with biosolids in Jordan. During 2004 an estimated 260,000 m3 of liquid sludge and 12,000 m3 of dewatered biosolids were generated in Jordan. Little information is available on the quality of biosolids in developing countries. The goal of this study was to assess the quality of biosolids generated after solar drying at two wastewater treatment plants in Jordan. The concentration of metals met requirements for exceptional quality biosolids based upon United States Environmental Protection Agency limits, however, based upon fecal coliform levels they would be consider Class B biosolids. © 2007 DEStech Publications, Inc.
• Al-Hmoud, N., O'Shaughnessy, S., Suleiman, W., Gerba, C. P., & Choi, C. Y. (2006). Disinfection of enteric bacterial pathogens and indicators in biosolids using solar drying in Jordan. Journal of Residuals Science and Technology, 3(4), 185-191.
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  Abstract: This study focuses on the use of solar drying to reduce the density level of enteric pathogens and indicators In biosolids In semi-arid locations. Seasonal solar drying studies were conducted in Wadi Hassan, Jordan by studying the die-off patterns of Salmonella spp. and fecal coliforms in biosolids. Two drying experiments were conducted in Wadi Hassan during warm dry periods and one was completed during a cold wet period. The average fecal coliform inactivation rates (Kd) during the warm dry periods were 0.18 days-1 and 0.19 days-1 during the summer 2004 and spring 2005 seasons, respectively. Class A criteria was met in roughly 20 days for both experiments. The average inactivation rate for fecal coliforms during the winter season was 0.04 days-1. Salmonella spp. densities dropped below Class A levels on Day 14 and on Day 19 In the summer 2004 and in the spring 2005 drying seasons, respectively. During the winter season, the colder temperatures, high relative humidity and rainfall events prevented the biosolids from reaching Class A bacterial levels. In semi-arid regions, during dry periods, open solar drying Is an economically viable and technically feasible method of disinfecting biosolids prior to reuse during warm dry periods. However, during the cold and wet months, open solar drying is not an effective method for disinfecting biosolids. © 2006 DEStech Publications, Inc.
• Gerba, C., Orosz-Coghlan, P. A., Rusin, P. A., Karpiscak, M. M., & Gerba, C. P. (2006). Microbial source tracking of Escherichia coli in a constructed wetland. Water environment research : a research publication of the Water Environment Federation, 78(3).
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  Little information has been gathered on the effect of avian species on the microbial water quality in constructed wetlands. To address this concern, fecal pollution from nonpoint and point sources was evaluated in a constructed wetland in Tolleson, Arizona. Antibiotic resistance profiling and biochemical fingerprinting were performed on 325 Escherichia coli isolates, collected from key points in the wetlands. Multivariate statistical analysis was used to interpret the data for samples collected on October 3 and December 12, 2000, and January 16, 2001. It was found that the passerine population was the major source of the Escherichia coli in the water samples collected in the wetlands on October 3 and December 12, 2000, whereas the regrowth in the treated municipal wastewater was the main source on January 16, 2001. This information is useful in providing data for operators in the monitoring of wetlands created for wastewater treatment and wildlife habitat.
• Nwachuku, N., & Gerba, C. P. (2006). Health risks of enteric viral infections in children. Reviews of Environmental Contamination and Toxicology, 186, 1-56.
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  PMID: 16676900;Abstract: Children are at a greater risk of infections from serious enteric viral illness than adults for a number of reasons. Most important is the immune system, which is needed to control the infection processes.This difference can lead to more serious infections than in adults, who have fully developed immune systems. There are a number of significant physiological and behavioral differences between adults and children that place children at a greater risk of exposure and a greater risk of serious infection from enteric viruses. Although most enteric viruses cause mild or asymptomatic infections, they can cause a wide range of serious and life-threatening illnesses in children. The peak incidence of most enteric viral illnesses is in children
• Orosz-Coghlan, P. A., Rusin, P. A., Karpiscak, M. M., & Gerba, C. P. (2006). Microbial source tracking of Escherichia coli in a constructed wetland. Water Environment Research, 78(3), 227-232.
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  PMID: 16629262;Abstract: Little information has been gathered on the effect of avian species on the microbial water quality in constructed wetlands. To address this concern, fecal pollution from nonpoint and point sources was evaluated in a constructed wetland in Tolleson, Arizona. Antibiotic resistance profiling and biochemical fingerprinting were performed on 325 Escherichia coli isolates, collected from key points in the wetlands. Multivariate statistical analysis was used to interpret the data for samples collected on October 3 and December 12, 2000, and January 16, 2001. It was found that the passerine population was the major source of the Escherichia coli in the water samples collected in the wetlands on October 3 and December 12, 2000, whereas the regrowth in the treated municipal wastewater was the main source on January 16, 2001. This information is useful in providing data for operators in the monitoring of wetlands created for wastewater treatment and wildlife habitat.
• Song, I., Stine, S. W., Choi, C. Y., & Gerba, C. P. (2006). Comparison of crop contamination by microorganisms during subsurface drip and furrow irrigation. Journal of Environmental Engineering, 132(10), 1243-1248.
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  Abstract: This study was conducted to compare subsurface drip irrigation (SDI) with furrow irrigation (FI) in crop contamination with microbial-contaminated water irrigation. Escherichia coli, Clostridium perfringens, and coliphage PRD-1 were added to water used to irrigate cantaloupe, lettuce, and bell pepper. Samples of produce, surface, and subsurface (10cm) soil for each irrigation system were collected on Days 1, 3, 5, 7, 10, and 14 after the application of the study microorganisms. Overall, greater contamination of produce occurred in FI plots than in SDI plots. The microorganisms were detected on the surfaces of cantaloupe and lettuce, but were never recovered on the bell peppers. The greatest amount of contamination occurred with PRD-1 on cantaloupe. The study microorganisms survived longer in the subsurface soil than the soil surface. PRD-1 showed greater persistence than E. coli in soil, while C. perfringens experienced little inactivation during the experiment periods. This study showed that subsurface drip irrigation has great potential to reduce health risks when microbial-contaminated water is used for irrigation water. © 2006 ASCE.
• Vidales-Contreras, J. A., Gerba, C. P., Karpiscak, M. M., Acuna-Askar, K., & Chaidez-Quiroz, C. (2006). Transport of coliphage PRD1 in a surface flow constructed wetland. Water Environment Research, 78(11), 2253-2260.
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  PMID: 17120444;Abstract: A tracer study was conducted in a 3-ha surface flow constructed wetland to analyze transport performance of PRD1, an enteric virus model. The convection-dispersion equation (CDE), including a first-order reaction model, adequately simulated transport performance of PRD1 in the wetland under an average hydraulic loading rate of 82 mm/d. Convective velocity (v) and longitudinal dispersion coefficient (D) were estimated by modeling a conservative tracer (bromide) pulse through the wetland. Both PRD1 and bromide were simultaneously added to the entering secondary treated wastewater effluent. The mass of bromide and PRD1 recovered was 76 and 16%, respectively. The PRD1 decay rate was calculated to be 0.3/day. The findings of this study suggest that -the CDE model and analytical moment equations represent a suitable option to characterize virus transport performance in surface flow constructed wetlands.
• Boone, S. A., & Gerba, C. P. (2005). The occurrence of influenza A virus on household and day care center fomites. Journal of Infection, 51(2), 103-109.
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  PMID: 16038759;Abstract: Objective. The goal of this study was to evaluate the prevalence of influenza A virus on surfaces in day care and home settings to better assess the potential role of fomites in the transmission of influenza. Methods. During two and a half years, 218 fomites were tested from 14 different day care centers. Ten different fomites from bathrooms, kitchens and play areas were sampled. In addition, 92 fomites from eight different homes with children were tested over 6 months. Fourteen different household fomites from bathrooms, kitchens and living areas were sampled. Influenza A viral RNA was detected using reverse transcriptase-polymerase chain reaction. Results. Influenza was detected on 23% of day care fomites sampled during the fall and 53% of fomites sampled during the spring. Spring and fall sample data was determined to be statistically different at the 0.05 α-level by Chi-square analysis P
• Brands, D. A., Inman, A. E., Gerba, C. P., Maré, C. J., Billington, S. J., Saif, L. A., Levine, J. F., & Joens, L. A. (2005). Prevalence of Salmonella spp. in oysters in the United States. Applied and Environmental Microbiology, 71(2), 893-897.
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  PMID: 15691945;PMCID: PMC546685;Abstract: Food-borne diseases such as salmonellosis can be attributed, in part, to the consumption of raw oysters. To determine the prevalence of Salmonella spp. in oysters, oysters harvested from 36 U.S. bays (12 each from the West, East, and Gulf coasts in the summer of 2002, and 12 bays, four per coast, in the winter of 2002-2003) were tested. Salmonella was isolated from oysters from each coast of the United States, and 7.4% of all oysters tested contained Salmonella. Isolation tended to be bay specific, with some bays having a high prevalence of Salmonella, while other bays had none. Differences in the percentage of oysters from which Salmonella was isolated were observed between the summer and winter months, with winter numbers much lower probably due to a variety of weather-related events. The vast majority (78/101) of Salmonella isolates from oysters were Salmonella enterica serovar Newport, a major human pathogen, confirming the human health hazard of raw oyster consumption. Contrary to previous findings, no relationship was found between the isolation of fecal coliforms and Salmonella from oysters, indicating a necessity for specific monitoring for Salmonella and other pathogens rather than the current reliance on fecal coliform testing.
• Brusseau, M. L., Oleen, J. K., Santamaria, J., Cheng, L., Orosz-Coghlan, P., Chetochine, A. S., Blanford, W. J., Rykwalder, P., & Gerba, C. P. (2005). Transport of microsporidium Encephalitozoon intestinales spores in sandy porous media. Water Research, 39(15), 3636-3642.
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  PMID: 16048729;Abstract: The retention and transport of microsporidium Encephalitozoon intestinales spores in two water-saturated sandy porous media was investigated in this study. The initial breakthrough of the spores in the column effluent occurred essentially simultaneously with that of a non-reactive tracer, indicating no significant velocity enhancement. A large fraction (45-73%) of the spores injected into the columns was not recovered in the effluent, indicating removal from solution through colloid retention processes of attachment and/or straining. The relative significance of attachment and straining to total retention was evaluated in additional experiments. An experiment was conducted with a sieved coarse fraction of porous media for which straining is unlikely to be of significance based on the relative diameters of the spores and porous-medium pores. The spore recovery for this experiment was similar to the recoveries obtained for microsporidia transport in the un-sieved parent porous medium. An additional experiment was conducted with a subsample of the coarse fraction that was acid-washed to reduce potential surface attachment sites. Spore recovery was complete for this experiment. These results suggest surface deposition was the primary removal mechanism in our system. This conclusion is supported by the results of an experiment wherein deionized water was flushed through a column that was previously flushed with electrolyte solution. The effluent spore concentrations were observed to increase upon injection of deionized water, indicating re-mobilization of spores upon a change in water chemistry. The measured data were successfully simulated using a mathematical model incorporating colloid filtration. The results of this study suggest that the transport of microspordia in sandy porous media is governed by established colloid-transport processes. © 2005 Elsevier Ltd. All rights reserved.
• Gerba, C. P., & Smith Jr., J. E. (2005). Sources of pathogenic microorganisms and their fate during land application of wastes. Journal of Environmental Quality, 34(1), 42-48.
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  PMID: 15647533;Abstract: The hazards associated with pathogens in land-applied animal and human wastes have long been recognized. Management of these risks requires an understanding of sources, concentrations, and removal by processes that may be used to treat the wastes; survival in the environment; and exposure to sensitive populations. The major sources are animal feeding operations, municipal wastewater treatment plant effluents, biosolids, and on-site treatment systems. More than 150 known enteric pathogens may be present in the untreated wastes, and one new enteric pathogen has been discovered every year over the past decade. There has been increasing demand that risks associated with the land treatment and application be better defined. For risks to be quantified, more data are needed on the concentrations of pathogens in wastes, the effectiveness of treatment processes, standardization of detection methodology, and better quantification of exposure.
• Gerba, C., Boone, S. A., & Gerba, C. P. (2005). The occurrence of influenza A virus on household and day care center fomites. The Journal of infection, 51(2).
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  The goal of this study was to evaluate the prevalence of influenza A virus on surfaces in day care and home settings to better assess the potential role of fomites in the transmission of influenza.
• Gerba, C., Reynolds, K. A., Watt, P. M., Boone, S. A., & Gerba, C. P. (2005). Occurrence of bacteria and biochemical markers on public surfaces. International journal of environmental health research, 15(3).
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  From 1999-2003, the hygiene of 1061 environmental surfaces from shopping, daycare, and office environments, personal items, and miscellaneous activities (i.e., gymnasiums, airports, movie theaters, restaurants, etc.), in four US cities, was monitored. Samples were analyzed for fecal and total coliform bacteria, protein, and biochemical markers. Biochemical markers, i.e., hemoglobin (blood marker), amylase (mucus, saliva, sweat, and urine marker), and urea (urine and sweat marker) were detected on 3% (26/801); 15% (120/801), and 6% (48/801) of the surfaces, respectively. Protein (general hygiene marker) levels > or = 200 microg/10 cm2 were present on 26% (200/801) of the surfaces tested. Surfaces from children's playground equipment and daycare centers were the most frequently contaminated (biochemical markers on 36%; 15/42 and 46%; 25/54, respectively). Surfaces from the shopping, miscellaneous activities, and office environments were positive for biochemical markers with a frequency of 21% (69/333), 21% (66/308), and 11% (12/105), respectively). Sixty samples were analyzed for biochemical markers and bacteria. Total and fecal coliforms were detected on 20% (12/60) and 7% (4/ 60) of the surfaces, respectively. Half and one-third of the sites positive for biochemical markers were also positive for total and fecal coliforms, respectively. Artificial contamination of public surfaces with an invisible fluorescent tracer showed that contamination from outside surfaces was transferred to 86% (30/ 35) of exposed individual's hands and 82% (29/35) tracked the tracer to their home or personal belongings hours later. Results provide information on the relative hygiene of commonly encountered public surfaces and aid in the identification of priority environments where contaminant occurrence and risk of exposure may be greatest. Children's playground equipment is identified as a priority surface for additional research on the occurrence of and potential exposure to infectious disease causing agents.
• Gerba, C., Song, I., Choi, C. Y., O'Shaughnessy, S., & Gerba, C. P. (2005). Effects of temperature and moisture on coliphage PRD-1 survival in soil. Journal of food protection, 68(10).
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  The goal of this study was to quantitatively assess the effects of temperature and soil moisture on the survival of coliphage PRD-1 in soil. PRD-1 was added to sandy loam soil at five different soil moisture levels. The soil seeded with PRD-1 was packed into sterile polyethylene jars and exposed to eight different temperatures in an oven. Samples were collected over 14 to 25 days depending on the temperature. The inactivation rate of PRD-1 increased linearly with increased temperature. The inactivation rate gradually decreased when the soil moisture level decreased from 20.9 to 8.9%. However, the inactivation rate increased when the soil moisture content reached 5.1%, suggesting the existence of an optimal soil moisture condition for PRD-1 survival. It is also possible that there is a threshold soil moisture level below which the inactivation of PRD-1 suddenly increases. Marked reductions in recoveries were observed as the soil moisture approached or fell below 5.0% as a result of evaporation. The increased inactivation of PRD-1 due to strong association with soil particles may have caused rapid reductions in recoveries. The evaporation process appeared to affect PRD-1 survival substantially at higher temperatures whereas little effect was observed at lower temperatures. A model developed from this study predicted PRD-1 survival in subsurface soil in field conditions with an average error of 11.0%.
• Gerba, C., Stine, S. W., Pepper, I. L., & Gerba, C. P. (2005). Contribution of drinking water to the weekly intake of heterotrophic bacteria from diet in the United States. Water research, 39(1).
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  The goal of this study was to assess the relative contribution of heterotrophic bacteria from various sources in the normal diet of an average person in the United States, due to concerns regarding the potential health implications of such bacteria in household tapwater. A literature search was conducted to determine the concentration of heterotrophic plate count (HPC) bacteria in drinking water, as well as foods common to the American diet. Food items were also obtained in Tucson, AZ to further evaluate the consumption of HPC and total coliform bacteria. This was compared to a recent study on HPC bacteria in tapwater with and without POU devices mounted on the tap in Tucson, AZ households. It was determined that only 0.048-4.5% of the average consumer's total heterotrophic bacteria intake is derived from drinking water. Thus, HPC bacteria in drinking water do not represent a significant exposure of total HPC bacteria in the average diet of consumers in the United States.
• Gerba, C., Stine, S. W., Song, I., Choi, C. Y., & Gerba, C. P. (2005). Application of microbial risk assessment to the development of standards for enteric pathogens in water used to irrigate fresh produce. Journal of food protection, 68(5).
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  Microbial contamination of the surfaces of cantaloupe, iceberg lettuce, and bell peppers via contact with irrigation water was investigated to aid in the development of irrigation water quality standards for enteric bacteria and viruses. Furrow and subsurface drip irrigation methods were evaluated with the use of nonpathogenic surrogates, coliphage PRD1, and Escherichia coli ATCC 25922. The concentrations of hepatitis A virus (HAV) and Salmonella in irrigation water necessary to achieve a 1:10,000 annual risk of infection, the acceptable level of risk used for drinking water by the U.S. Environmental Protection Agency, were calculated with a quantitative microbial risk assessment approach. These calculations were based on the transfer of the selected nonpathogenic surrogates to fresh produce via irrigation water, as well as previously determined preharvest inactivation rates of pathogenic microorganisms on the surfaces of fresh produce. The risk of infection was found to be variable depending on type of crop, irrigation method, and days between last irrigation event and harvest. The worst-case scenario, in which produce is harvested and consumed the day after the last irrigation event and maximum exposure is assumed, indicated that concentrations of 2.5 CFU/100 ml of Salmonella and 2.5 x 10(-5) most probable number per 100 ml of HAV in irrigation water would result in an annual risk of 1:10,000 when the crop was consumed. If 14 days elapsed before harvest, allowing for die-off of the pathogens, the concentrations were increased to 5.7 x 10(3) Salmonella per 100 ml and 9.9 x 10(-3) HAV per 100 ml.
• Gerba, C., Stine, S. W., Song, I., Choi, C. Y., & Gerba, C. P. (2005). Effect of relative humidity on preharvest survival of bacterial and viral pathogens on the surface of cantaloupe, lettuce, and bell peppers. Journal of food protection, 68(7).
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  The purpose of this study was to compare the effects of humidity on the preharvest survival of microbial pathogens on cantaloupe, lettuce, and bell peppers. An additional goal was to evaluate Clostridium perfringens as an indicator of fecal contamination on produce. The microorganisms used in this study included Escherichia coli, E. coli O157:H7, Shigella sonnei, Salmonella enterica subsp. enterica, Clostridium perfringens, hepatitis A virus (HAV), feline calicivirus (FCV), and coliphage PRD1. The study took place in a controlled environment chamber that allowed for the control of temperature (18 to 26 degrees C) and relative humidity. Survival rates under high (mean, 85.7 to 90.3%) and low (mean, 45.1 to 48.4%) relative humidity were compared. The surfaces of the edible portion of each plant were inoculated with the study microorganisms. Samples were collected throughout 2 weeks. More microorganisms survived significantly longer (P < 0.05) on cantaloupe than on lettuce and bell peppers. The type of produce on which each organism experienced the highest inactivation rate tended to change with relative humidity. The survival of microorganisms on produce surfaces was not uniformly affected by relative humidity. Of the studied microorganisms, HAV, PRD1, and C. perfringens were found to have the lowest inactivation rates, whereas FCV and E. coli ATCC 25922 tended to become inactivated most rapidly. C. perfringens generally survived longer than all other bacteria and FCV in all experiments. This trend suggests that C. perfringens may be an acceptable indicator of bacterial contamination and survival in various environments and on different types of crops.
• Gerba, C., Stine, S. W., Vladich, F. D., Pepper, I. L., & Gerba, C. P. (2005). Development of a method for the concentration and recovery of microsporidia from tap water. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 40(5).
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  Microsporidia are obligate intracellular parasites. Microsporidian spores infect a wide variety of hosts, including humans. The spores may be found in infected hosts' urine and feces, thus waterborne transmission is possible. This study details method development for the detection of microsporidia in tap water. In this study, filtration, centrifugation, purification, and detection parameters were optimized for the detection of microsporidia. The Pall-Gelman Envirocheck sampling capsule (Pall Gelman, Ann Arbor, MI) was chosen as the filter element. Optimal centrifugal force for spore recovery was 1500 x g. Additionally, it was determined that eluting microsporidia spores in a detergent elution buffer solution had a detrimental effect on spore recovery. A direct examination of the concentrate resulted in a greater recovery with less variability than subjecting the sample concentrate to a Percoll-sucrose density gradient purification step. The staining method employed for the detection spores was Calcofluor white (Sigma, St. Louis, MO). Percent recoveries for 10 L tap water samples (n = 5) using the Envirocheck sampling capsule without a density gradient purification step were 26.1+/-13.4 compared to 25+/-13.8 for samples subjected to a density gradient purification step.
• Haas, C. N., Marie, J. R., Rose, J. B., & Gerba, C. P. (2005). Assessment of benefits from use of antimicrobial hand products: Reduction in risk from handling ground beef. International Journal of Hygiene and Environmental Health, 208(6), 461-466.
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  PMID: 16325555;Abstract: Quantitative microbial risk assessment (QMRA) has been used to estimate the benefits resulting from the use of hand cleansing products (e.g., soaps) containing anti-microbial ingredients. This was done by developing a model for the scenario of hand contact with ground beef during food preparation, considering transference of bacteria to the hands, removal and inactivation by handwashing, and subsequent transference from the hands to the mouth. Organisms of interest in this case study were pathogenic Escherichia coli and the particular strain E. coli O157:H7. It was found that QMRA could be applied to this problem, and that the antimicrobials provided some quantifiable benefit (i.e., reduced the risk of infection and illness). Benefits from the use of triclosan-containing products were less than from the use of products in which alcohols or chlorhexidine were active ingredients. © 2005 Elsevier GmbH. All rights reserved.
• John, D. E., Haas, C. N., Nwachuku, N., & Gerba, C. P. (2005). Chlorine and ozone disinfection of Encephalitozoon intestinalis spores. Water Research, 39(11), 2369-2375.
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  PMID: 15921720;Abstract: Microsporidia are intracellular eukaryotic parasites which have the potential for zoonotic and environmental, including waterborne, transmission. Encephalitozoon intestinalis is a microsporidian pathogen of humans and animals and has been detected in surface water. It is also on the Contaminant Candidate List of potential emerging waterborne pathogens for the US EPA. We performed disinfection studies using chlorine and ozone on E. intestinalis spores with a cell-culture most-probable-number assay to determine infectivity. Chlorine experiments were performed at 5°C at pH of 6, 7, and 8 with 1 mg/L initial chlorine concentrations, while ozone experiments were performed at 5°C and pH 7 with initial ozone doses of 1 and 0.5 mg/L, both in buffered water. A derivation of Hom's model for disinfection kinetics under dynamic disinfectant concentrations was used to fit observed data and calculate concentration-time product (C*t) values. Chlorine C*t values varied with pH such that 99% (2-log10) C*t ranged from 12.8 at pH 6 to 68.8 at pH 8 (mg min/L). Ozone C*t values were approximately an order of magnitude less at 0.59-0.84 mg min/L, depending on initial concentration. © 2005 Elsevier Ltd. All rights reserved.
• Nwachuku, N., Gerba, C. P., Oswald, A., & Mashadi, F. D. (2005). Comparative inactivation of adenovirus serotypes by UV light disinfection. Applied and Environmental Microbiology, 71(9), 5633-5636.
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  PMID: 16151167;PMCID: PMC1214670;Abstract: The results of this study confirm that adenoviruses are the most resistant enteric viruses to inactivation by UV light and that adenovirus 40 appears to be the most resistant. The effect of freeze-thawing and storage in water may affect the sensitivity of some adenoviruses to inactivation by UV light. Copyright © 2005, American Society for Microbiology. All Rights Reserved.
• Reynolds, K. A., Watt, P. M., Boone, S. A., & Gerba, C. P. (2005). Occurrence of bacteria and biochemical markers on public surfaces. International Journal of Environmental Health Research, 15(3), 225-234.
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  PMID: 16134485;Abstract: From 1999-2003, the hygiene of 1061 environmental surfaces from shopping, daycare, and office environments, personal items, and miscellaneous activities (i.e., gymnasiums, airports, movie theaters, restaurants., etc.), in four US cities, was monitored. Samples were analyzed for fecal and total coliform bacteria, protein, and biochemical markers. Biochemical markers, i.e., hemoglobin (blood marker), amylase (mucus, saliva, sweat, and urine marker), and urea (urine and sweat marker) were detected on 3% (26/801); 15% (120/801), and 6% (48/801) of the surfaces, respectively. Protein (general hygiene marker) levels ≥ 200 μg/10 cm2 were present on 26% (200/801) of the surfaces tested. Surfaces from children's playground equipment and daycare centers were the most frequently contaminated (biochemical markers on 36%; 15/42 and 46%; 25/54, respectively). Surfaces from the shopping, miscellaneous activities, and office environments were positive for biochemical markers with a frequency of 21% (69/333), 21% (66/308), and 11% (12/105), respectively). Sixty samples were analyzed for biochemical markers and bacteria. Total and fecal coliforms were detected on 20% (12/60) and 7% (4/60) of the surfaces, respectively. Half and one-third of the sites positive for biochemical markers were also positive for total and fecal coliforms, respectively. Artificial contamination of public surfaces with an invisible fluorescent tracer showed that contamination from outside surfaces was transferred to 86% (30/35) of exposed individual's hands and 82% (29/35) tracked the tracer to their home or personal belongings hours later. Results provide information on the relative hygiene of commonly encountered public surfaces and aid in the identification of priority environments where contaminant occurrence and risk of exposure may be greatest. Children's playground equipment is identified as a priority surface for additional research on the occurrence of and potential exposure to infectious disease causing agents. © 2005 Taylor & Francis Group Ltd.
• Song, I., Choi, C. Y., O'Shaughnessy, S., & Gerba, C. P. (2005). Effects of temperature and moisture on coliphage PRD-1 survival in soil. Journal of Food Protection, 68(10), 2118-2122.
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  PMID: 16245716;Abstract: The goal of this study was to quantitatively assess the effects of temperature and soil moisture on the survival of coliphage PRD-1 in soil. PRD-1 was added to sandy loam soil at five different soil moisture levels. The soil seeded with PRD-1 was packed into sterile polyethylene jars and exposed to eight different temperatures in an oven. Samples were collected over 14 to 25 days depending on the temperature. The inactivation rate of PRD-1 increased linearly with increased temperature. The inactivation rate gradually decreased when the soil moisture level decreased from 20.9 to 8.9%. However, the inactivation rate increased when the soil moisture content reached 5.1%, suggesting the existence of an optimal soil moisture condition for PRD-1 survival. It is also possible that there is a threshold soil moisture level below which the inactivation of PRD-1 suddenly increases. Marked reductions in recoveries were observed as the soil moisture approached or fell below 5.0% as a result of evaporation. The increased inactivation of PRD-1 due to strong association with soil particles may have caused rapid reductions in recoveries. The evaporation process appeared to affect PRD-1 survival substantially at higher temperatures whereas little effect was observed at lower temperatures. A model developed from this study predicted PRD-1 survival in subsurface soil in field conditions with an average error of 11.0%. Copyright ©, International Association for Food Protection.
• Stine, S. W., Song, I., Choi, C. Y., & Gerba, C. P. (2005). Application of microbial risk assessment to the development of standards for enteric pathogens in water used to irrigate fresh produce. Journal of Food Protection, 68(5), 913-918.
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  PMID: 15895721;Abstract: Microbial contamination of the surfaces of cantaloupe, iceberg lettuce, and bell peppers via contact with irrigation water was investigated to aid in the development of irrigation water quality standards for enteric bacteria and viruses. Furrow and subsurface drip irrigation methods were evaluated with the use of nonpathogenic surrogates, coliphage PRD1, and Escherichia coli ATCC 25922. The concentrations of hepatitis A virus (HAV) and Salmonella in irrigation water necessary to achieve a 1:10,000 annual risk of infection, the acceptable level of risk used for drinking water by the U.S. Environmental Protection Agency, were calculated with a quantitative microbial risk assessment approach. These calculations were based on the transfer of the selected nonpathogenic surrogates to fresh produce via irrigation water, as well as previously determined preharvest inactivation rates of pathogenic microorganisms on the surfaces of fresh produce. The risk of infection was found to be variable depending on type of crop, irrigation method, and days between last irrigation event and harvest. The worst-case scenario, in which produce is harvested and consumed the day after the last irrigation event and maximum exposure is assumed, indicated that concentrations of 2.5 CFU/100 ml of Salmonella and 2.5 × 10-5 most probable number per 100 ml of HAV in irrigation water would result in an annual risk of 1:10,000 when the crop was consumed. If 14 days elapsed before harvest, allowing for die-off of the pathogens, the concentrations were increased to 5.7 × 103 Salmonella per 100 ml and 9.9 × 10-3 HAV per 100 ml. Copyright ©, International Association for Food Protection.
• Stine, S. W., Song, I., Choi, C. Y., & Gerba, C. P. (2005). Effect of relative humidity on preharvest survival of bacterial and viral pathogens on the surface of cantaloupe, lettuce, and bell peppers. Journal of Food Protection, 68(7), 1352-1358.
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  PMID: 16013370;Abstract: The purpose of this study was to compare the effects of humidity on the preharvest survival of microbial pathogens on cantaloupe, lettuce, and bell peppers. An additional goal was to evaluate Clostridium perfringens as an indicator of fecal contamination on produce. The microorganisms used in this study included Escherichia coli, E. coli O157:H7, Shigella sonnei, Salmonella enterica subsp. enterica, Clostridium perfringens, hepatitis A virus (HAV), feline calicivirus (FCV), and coliphage PRD1. The study took place in a controlled environment chamber that allowed for the control of temperature (18 to 26°C) and relative humidity. Survival rates under high (mean, 85.7 to 90.3%) and low (mean, 45.1 to 48.4%) relative humidity were compared. The surfaces of the edible portion of each plant were inoculated with the study microorganisms. Samples were collected throughout 2 weeks. More microorganisms survived significantly longer (P < 0.05) on cantaloupe than on lettuce and bell peppers. The type of produce on which each organism experienced the highest inactivation rate tended to change with relative humidity. The survival of microorganisms on produce surfaces was not uniformly affected by relative humidity. Of the studied microorganisms, HAV, PRD1, and C. perfringens were found to have the lowest inactivation rates, whereas FCV and E. coli ATCC 25922 tended to become inactivated most rapidly. C. perfringens generally survived longer than all other bacteria and FCV in all experiments. This trend suggests that C. perfringens may be an acceptable indicator of bacterial contamination and survival in various environments and on different types of crops. Copyright ©, International Association for Food Protection.
• Thurston-Enriquez, J. A., Haas, C. N., Jacangelo, J., & Gerba, C. P. (2005). Inactivation of enteric adenovirus and feline calicivirus by chlorine dioxide. Applied and Environmental Microbiology, 71(6), 3100-3105.
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  PMID: 15933007;PMCID: PMC1151811;Abstract: Chlorine dioxide (ClO2) inactivation experiments were conducted with adenovirus type 40 (AD40) and feline calicivirus (FCV). Experiments were carried out in buffered, disinfectant demand-free water under high- and low-pH and -temperature conditions. Ct values (the concentration of ClO2 multiplied by contact time with the virus) were calculated directly from bench-scale experiments and from application of the efficiency factor Hom (EFH) model. AD40 Ct ranges for 4-log inactivation (Ct99.99%) at 5°C were >0.77 to 0.80 to 0.49 to 4.20 to
• Thurston-Enriquez, J. A., Haas, C. N., Jacangelo, J., & Gerba, C. P. (2005). Inactivation of enteric adenovirus and feline calicivirus by ozone. Water Research, 39(15), 3650-3656.
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  PMID: 16061270;Abstract: Little information is available regarding the effectiveness of ozone on the inactivation of caliciviruses and enteric adenoviruses. Inactivation experiments were conducted with feline calicivirus (FCV), closely related to the human caliciviruses based on nucleic acid organization and capsid architecture, and adenovirus type 40 (AD40). Experiments were carried out in buffered disinfectant demand free water at pH 7 and 5°C. Ct values; concentration of ozone multiplied by contact time with virus; were determined from application of the efficiency factor hom (EFH) model. Ct values for 4-log (99.99%) ozone inactivation at 5°C and pH 7 ranged from 0.07 to 0.60 mg/l min for AD40 and
• Chaidez, C., & Gerba, C. P. (2004). Comparison of the microbiologic quality of point-of-use (POU)-treated water and tap water. International Journal of Environmental Health Research, 14(4), 253-260.
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  PMID: 15369990;Abstract: Activated carbon filtration devices placed on household faucets are used to improve the taste and odour of tap water. However, there has been a concern that the growth of bacteria capable of causing opportunistic infections in these devices might present a public health risk. The water quality from point-of-use (POU) water activated carbon treatment devices and that of tap water with POU-connections and tap water without POU devices were compared. Heterotrophic plate count (HPC) bacteria, total and faecal coliforms, and acid-fast organisms (Mycobacteria spp.), as well as, the opportunistic bacterial pathogens Aeromonas hydrophila, Plesiomonas shigelloides, and Pseudomonas aeruginosa were enumerated. The highest concentration of bacteria was found in POU-treated water. P. aeruginosa, acid-fast organisms, and total coliforms were present in 38.5, 43.8, and 82.4% of the samples, respectively. HPC bacteria were present in all of the POU-treated water samples, with concentrations ranging from 10 2 to 107 colony forming units/mL. Neither faecal coliforms nor P. shigelloides were recovered from any samples. Tap water with a POU-connection also had higher numbers of bacteria than tap water samples. It was concluded that tap water without POU devices had lower numbers of A. hydrophila, acid-fast organisms, HPC bacteria, P. aeruginosa and coliforms than POU-treated water, and tap water with a POU-connection. The use of POU-devices may amplify the numbers of bacteria present in the tapwater by promoting biofilm formation. Based on a daily ingestion of two liters of POU treated water, A. hydrophila and P. aeruginosa had a probability of less than 10-6 of colonizing the gut; however, annual risks could be as much as 100-fold greater.
• Choi, C., Song, I., Stine, S., Pimentel, J., & Gerba, C. (2004). Role of irrigation and wastewater reuse: Comparison of subsurface irrigation and furrow irrigation. Water Science and Technology, 50(2), 61-68.
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  PMID: 15344774;Abstract: Two different irrigation systems, subsurface drip irrigation and furrow irrigation, are tested to investigate the level of viral contamination and survival when tertiary effluent is used in and and semi-arid regions. The effluent was injected with bacteriophages of PRD1 and MS2. A greater number of PRD1 and MS2 were recovered from the lettuce in the subsurface drip-irrigated plots as compared to those in the furrow-irrigated plots. Shallow drip tape installation and preferential water paths through cracks on the soil surface appeared to be the main causes of high viral contamination in subsurface drip irrigation plots, which led to the direct contact of the lettuce stems with the irrigation water which penetrated the soil surface. The water use efficiency of the subsurface drip irrigation system was higher than that of the furrow irrigation system. Thus, subsurface drip irrigation is an efficient irrigation method for vegetable crops in arid and semi- arid regions if viral contamination can be reduced. Deeper installation of drip tapes, frequent irrigations, and timely harvests based on cumulative heat units may further reduce health risks by ensuring viral die-off under various field conditions. © IWA Publishing 2004.
• Gerba, C., Karim, M. R., Manshadi, F. D., Karpiscak, M. M., & Gerba, C. P. (2004). The persistence and removal of enteric pathogens in constructed wetlands. Water research, 38(7).
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  Sedimentation is thought to be one of the mechanisms of microbial reduction from wetlands used for wastewater treatment. This study compared the occurrence and survival of enteric indicator microorganisms and pathogens in the water column and sediments of two constructed surface flow wetlands in Arizona. On a volume/wet weight basis the concentration of fecal coliforms and coliphage in the water column and sediment was similar. However, on a volume/dry weight basis the numbers were one to two orders of magnitude higher in the sediment. Giardia cyst and Cryptosporidium oocyst concentrations were one to three orders of magnitude greater in the sediment compared to the water column. The die-off rates of all the bacteria and coliphage were greater in the water column than the sediment. The die-off rates of fecal coliforms in the water and sediment were 0.256log(10)day(-1) and 0.151log(10)day(-1), respectively. The die-off rates of Salmonella typhimurium in the water and sediment were 0.345log(10)day(-1) and 0.312log(10)day(-1), respectively. The die-off rates of naturally occurring coliphage in water column and sediment were 0.397log(10)day(-1) and 0.107log(10)day(-1), respectively, and the die-off rates of and PRD-1 in water and sediment were 0.198log(10)day(-1) and 0.054log(10)day(-1), respectively. In contrast Giardia die-off in the sediment was greater compared to the water column. The die-off rates of Giardia in water and sediment were 0.029log(10)day(-1) and 0.37log(10)day(-1), respectively. Coliphage survived the longest of any group of organisms in the sediment and the least in the water column. In contrast Giardia survived best in the water column and least in the sediment.
• Gerba, C., Pantoja, C. R., Navarro, S. A., Naranjo, J., Lightner, D. V., & Gerba, C. P. (2004). Nonsusceptibility of primate cells to Taura syndrome virus. Emerging infectious diseases, 10(12).
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  Taura syndrome virus (TSV), a pathogen of penaeid shrimp and member of the family Dicistroviridae, was recently reported to have the ability to infect primate cells. We independently retested this hypothesis. Three lines of primate cells FRhK-4, MA-104, and BGMK, which are highly susceptible to infection by human picornaviruses, were challenged with TSV. Viral replication was assayed by real-time reverse transcription-polymerase chain reaction using cell media samples collected on days 0, 4, and 7 postchallenge. By day 7, genome copy numbers had decreased 25%-99%. No cytopathic effect was observed after 7 days. An in situ hybridization assay, with gene probes specific for detection of TSV, was negative for TSV in challenged cells. The infectivity of residual virus in the cell culture media at day 7 was confirmed by bioassay using TSV-free indicator shrimp (Litopenaeus vannamei). TSV did not infect the primate cells tested, and no evidence of zoonotic potential was found.
• Karim, M. R., Manshadi, F. D., Karpiscak, M. M., & Gerba, C. P. (2004). The persistence and removal of enteric pathogens in constructed wetlands. Water Research, 38(7), 1831-1837.
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  PMID: 15026238;Abstract: Sedimentation is thought to be one of the mechanisms of microbial reduction from wetlands used for wastewater treatment. This study compared the occurrence and survival of enteric indicator microorganisms and pathogens in the water column and sediments of two constructed surface flow wetlands in Arizona. On a volume/wet weight basis the concentration of fecal coliforms and coliphage in the water column and sediment was similar. However, on a volume/ dry weight basis the numbers were one to two orders of magnitude higher in the sediment. Giardia cyst and Cryptosporidium oocyst concentrations were one to three orders of magnitude greater in the sediment compared to the water column. The die-off rates of all the bacteria and coliphage were greater in the water column than the sediment. The die-off rates of fecal coliforms in the water and sediment were 0.256log10day-1 and 0.151log 10day-1, respectively. The die-off rates of Salmonella typhimurium in the water and sediment were 0.345log10day -1 and 0.312log10day-1, respectively. The die-off rates of naturally occurring coliphage in water column and sediment were 0.397log10day-1 and 0.107log10day -1, respectively, and the die-off rates of and PRD-1 in water and sediment were 0.198log10day-1 and 0.054log 10day-1, respectively. In contrast Giardia die-off in the sediment was greater compared to the water column. The die-off rates of Giardia in water and sediment were 0.029log10day-1 and 0.37log10day-1, respectively. Coliphage survived the longest of any group of organisms in the sediment and the least in the water column. In contrast Giardia survived best in the water column and least in the sediment. © 2004 Elsevier Ltd. All rights reserved.
• Nwachcuku, N., & Gerba, C. P. (2004). Emerging waterborne pathogens: Can we kill them all?. Current Opinion in Biotechnology, 15(3), 175-180.
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  PMID: 15193323;Abstract: The rapid emergence of Cryptosporidium parvum and Escherichia coli 0157:H7 have created a threat to the drinking water industry and there is a growing need to develop a strategy for recognizing potential emerging waterborne pathogens. Globalization of trade, changing population demographics and changes in treatment technology have been driving factors in the emergence of these new pathogens. An understanding of disinfectant action and microbial resistance to treatment processes is needed to better identify those pathogens likely to be of greatest concern. Recent research on microbial resistance to treatment and disinfection demonstrates that the microbial surface structure and composition and the nature of the genome are key to determining the potential for waterborne transmission of emerging pathogens.
• Nwachuku, N., & Gerba, C. P. (2004). Health effects of Acanthamoeba spp. and its potential for waterborne transmission.. Reviews of environmental contamination and toxicology, 180, 93-131.
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  PMID: 14561077;Abstract: Risk from Acanthamoeba keratitis is complex, depending upon the virulence of the particular strain, exposure, trauma, or other stress to the eye, and host immune response. Bacterial endosymbionts may also play a factor in the pathogenicity of Acanthamoeba. Which factor(s) may be the most important is not clear. The ability of the host to produce IgA antibodies in tears may be a significant factor. The immune response of the host is a significant risk factor for GAE infection. If so, then a certain subpopulation with an inability to produce IgA in the tears may be at greatest risk. There was no sufficient data on the occurrence or types of Acanthamoeba in tapwater in the U.S. Published work on amoebal presence in tapwater does not provide information on the type of treatment the water received or the level of residual chlorine. Assessment of the pathogenicity by cell culture and molecular methods of Acanthamoeba in tapwater would also be useful in the risk assessment process for drinking water. The possibility that Acanthamoeba spp. might serve as vectors for bacterial infections from water sources also should be explored. The bacterial endosymbionts include an interesting array of pathogens such as Vibrio cholerae and Legionella pneumophila, both of which are well recognized waterborne/water-based pathogens. Work is needed to determine if control of Acanthamoeba spp. is needed to control water-based pathogens in water supplies.
• Nwachuku, N., & Gerba, C. P. (2004). Microbial risk assessment: Don't forget the children. Current Opinion in Microbiology, 7(3), 206-209.
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  PMID: 15196486;Abstract: Quantitative microbial risk assessment is a rapidly developing field with a purpose to quantify risks of infection, disease and mortality from the environmental exposure of pathogens. It is currently being applied to the development of standards for drinking water, wastewater re-use and foods. A growing body of evidence indicates that the greatest risk of infection for enteric pathogens is for persons less than 19 years of age. Children are more likely to become ill from consumption of contaminated drinking water and recreational activities. These increased risks may be because immunological, neurological and digestive systems are still developing. In addition, children are more environmentally exposed to pathogens. For some enteric pathogens children may be the greatest at risk population.
• Tanner, B. D., Kuwahara, S., Gerba, C. P., & Reynolds, K. A. (2004). Evaluation of electrochemically generated ozone for the disinfection of water and wastewater. Water Science and Technology, 50(1), 19-25.
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  PMID: 15318481;Abstract: Effective wastewater treatment is critical to public health and well-being. This is especially true in developing countries, where disinfection of wastewater is frequently inadequate. People who live in these areas may benefit from wastewater disinfection using ozone. This study evaluated the ability of a new electrochemical process of ozone generation, which produced ozone continuously at high pressure and concentration by the electrolysis of water, to disinfect tap water and secondarily treated wastewater. Inactivation of Klebsiella terrigena, Escherichia coli, MS2 bacteriophage and poliovirus 1 was evaluated first in reverse osmosis (RO) treated water. Inactivation of K. terrigena (6-log), E. coli (6-log), MS2 (6-log) and poliovirus 1 (>3-log) was observed after 1 min of ozonation in a 1L batch reactor. Experiments were then performed to assess the microbiological impact of disinfection using ozone on secondarily treated municipal wastewater. The effect of ozonation on wastewater was determined for total and faecal coliforms, bacteriophages and heterotrophic plate count (HPC) bacteria. Electrochemical ozone generators provided an effective, rapid and low-cost method of wastewater disinfection. Based on the results of this research, electrochemically generated ozone would be well suited to remote, small-scale, disinfection operations and may provide a feasible means of wastewater disinfection in developing countries. © IWA Publishing 2004.
• Abbaszadegan, M., Lechevallier, M., & Gerba, C. (2003). Occurrence of Viruses in US groundwaters. Journal / American Water Works Association, 95(9), 107-120+12.
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  Abstract: In a study that may affect the upcoming Ground Water Rule, the authors of this article determined that because of the widespread occurrence of virus in groundwater, most well water supplies should be disinfected before distribution. Scientific data were needed to support the upcoming rule, and this study provides a snapshot of viral contamination of groundwater at the nation al level. This article looks at information regarding the occurrence of pathogens and microbial indicators in source waters and their relationships with different abiotic parameters such as water quality, geologic formation of groundwater sites, and other factors. Sites were selected based on their geological characteristics to match the national profile for groundwater sources. Two different microbial methods were used to detect viruses in groundwater sources, and during the study a new microbial detection methodology was field-tested. Results indicate that when a well tested positive once for any of the biological assays, it was likely to test positive in future samplings. This article also offers a strategy to predict the vulnerability of groundwater supplies to fecal contamination.
• Enriquez, C., Alum, A., Suarez-Rey, E. M., Choi, C. Y., Oron, G., & Gerba, C. P. (2003). Bacteriophages MS2 and PRD1 in turfgrass by subsurface drip irrigation. Journal of Environmental Engineering, 129(9), 852-857.
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  Abstract: The contamination of turfgrass by bacteriophages MS-2 and PRD-1 was assessed in the field under sprinkler irrigation (SI) and subsurface drip irrigation (SDI). No contamination of turfgrass by MS-2 was observed using SDI in the summer or winter seasons. In the summer, PRD-1 was detected in low numbers in SDI turfgrass; however, at significantly lower numbers than in SI turfgrass (p
• Gerba, C. P., & Kayed, D. (2003). Caliciviruses: A major cause of foodborne illness. Journal of Food Science, 68(4), 1136-1142.
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  Abstract: The public health impact of infections by human caliciviruses (HuCVs) is increasingly being recognized. The Norwalk-like viruses (NLV) are the most common cause of outbreaks of nonbacterial gastroenteritis and the most recognized foodborne viral etiologic agents. Factors that contribute to their high burden of infection are low infectious dose, stability in the environment, the diversity of strains, and the lack of long-term immunity to infection or illness. The recent development of sensitive molecular techniques for diagnosis, quantification, and characterization of these agents has led to the recognition of the importance of NLV infection. Future applications of these approaches to understanding modes of transmission and the effectiveness of control measures holds promise for improved understanding of the epidemiology of HuCVs, as well as important control measures for foodborne transmission. This report reviews what is currently known and understood about human caliciviruses regarding foodborne transmission.
• Gerba, C. P., & Rose, J. B. (2003). International guidelines for water recycling: Microbiological considerations. Water Science and Technology: Water Supply, 3(4), 311-316.
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  Abstract: The World Health Organization and others have proposed international guidelines for the safe reuse of domestic wastewater. Treatment and microbial standards have been suggested with varying microbial water quality targets to suit local circumstances of affordability and health risks. However, it is important to recognize that universal application of bacterial standards for water quality assessment will not yield the same risks from microbial pathogens in reclaimed wastewater around the world. The concentration and types of pathogens in raw wastewater varies from one region of the world to another depending on the incidence in the community. This is influenced by the general hygiene, season, and per capita water use. Also, different treatment processes may be more effective in removing indicator bacteria and certain groups of pathogens than others. Proposed guidelines have also neglected the importance of water in the transmission of viral and bacterial diseases in developed countries and their impact on morbidity and mortality. Additional research is needed to better reduce the uncertainly of proposed guidelines for water recycling and to better define the risks associated to the exposed populations.
• Gerba, C. P., Nwachuku, N., & Riley, K. R. (2003). Disinfection resistance of waterborne pathogens on the United States Environmental Protection Agency's Contaminant Candidate List (CCL). Journal of Water Supply: Research and Technology - AQUA, 52(2), 81-94.
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  Abstract: In 1999, the United States Environmental Protection Agency developed a list of emerging waterborne microbial pathogens that may pose a risk in drinking water. This review deals with the disinfection resistance of microorganisms on the Contaminate Candidate List or CCL. Current disinfection practices in the United States appear to be capable of dealing with most of the microorganisms on the CCL, with the exception of Mycobacterium avium and adenoviruses. Mycobacterium avium is more resistant to most disinfectants than other waterborne bacteria and adenoviruses are the most resistant waterborne microorganisms to inactivation by ultraviolet disinfection. The microsporidium, Encephalitozoon intestinalis, shows significant resistance to inactivation by chemical disinfectants and further research on additional species of microsporidia appears to be warranted.
• Gerba, C. P., Riley, K. R., Nwachuku, N., Ryu, H., & Abbaszadegan, M. (2003). Removal of encephalitozoon intestinalis, calicivirus, and coliphages by conventional drinking water treatment. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 38(7), 1259-1268.
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  PMID: 12916850;Abstract: The removal of the Microsporidia, Encephalitozoon intestinalis, feline calicivirus and coliphages MS-2, PRD-1, and Fr were evaluated during conventional drinking water treatment in a pilot plant. The treatment consisted of coagulation, sedimentation, and mixed media filtration. Fr coliphage was removed the most (3.21 log), followed by feline calicivirus (3.05 log), E. coli (2.67 log), E. intestinalis (2.47 log), MS-2 (2.51 log), and PRD-1 (1.85 log). With the exception of PRD-1 the greatest removal of the viruses occurred during the flocculation step of the water treatment process.
• Kuwahara, S., Cuello, J., Reynolds, K., & Gerba, C. (2003). Synergistic UV-ozone effects on the treatment of pathogens in secondary effluent. SAE Technical Papers.
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  Abstract: Ozone and ultraviolet (UV) light have been shown to be effective in treating emerging pathogens that are not affected by the current standard treatment of chlorine. The hypothesis of this study was that a combined treatment of UV light and ozone would result in greater pathogen reduction than a large dose of either one individually. In the one-way studies for ozone and UV light, the ozone treatments took at least twice as long as the UV treatments to achieve the same extent of reduction in the microbial population. Specifically, 60 min for ozone and 30 min for UV light for a 4-log reduction in Heterotrophic plate counts (HPC's); 10 min for ozone and 3 min for UV light for a 3-log reduction in total coliforms and fecal coliforms; and, 6 min for ozone and 3 min for UV light for a 2-log reduction in coliphage. The ozone treatments, however, unlike the UV treatments, resulted in no positive re-growth in bacteria after treatment. Ozone and UV light acting simultaneously exhibited not merely additive, but synergistic effects, in reducing the microbial populations, with the exception of when low levels (2 min UV and 1 min ozone) of both factors were used. Specifically, the following treatment combinations yielded the maximum microbial reductions: low level of UV (1 min) and high level of ozone (4 min) for HPC's; high level of UV (2 min) and high level of ozone (4 min) for total Coliforms and fecal coliforms; and either one of the foregoing treatments for the overall microbial population. The synergistic effects between UV light and ozone allowed for lower UV and ozone levels to achieve the same extent of microbial reduction achieved by either factor acting separately. Thus, 2 min of ozone and 2 min of UV light applied simultaneously was just as effective as 6-8 min of ozone only or 2.5 min of UV light only. This synergistic effect should lead to reduced energy consumption while maintaining the level of disinfection required. If UV light and ozone were to be applied successively, the most effective sequence of application would be ozone first followed by UV light. Copyright © 2003 SAE International.
• Mena, K. D., Gerba, C. P., Haas, C. N., & Rose, J. B. (2003). Risk assessment of waterborne coxsackievirus. Journal / American Water Works Association, 95(7), 122-131+12.
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  Abstract: Coxsackieviruses are the most common nonpolio enteroviruses found in domestic wastewater and in contaminated surface water, groundwater, and drinking water. These viruses can cause vomiting, fever, headache, rash, and diarrhea and result in such serious outcomes as aseptic meningitis, myocarditis, respiratory illness, encephalitis, and insulin-dependent diabetes mellitus. Previous research investigating enteroviruses in water samples treated the enteroviruses as a group and did not focus on specific viruses. This article describes a risk assessment approach to evaluate the potential public health effects associated with drinking water and recreational waters contaminated by coxsackievirus. An exponential model developed from human dose-response studies was used to describe the infectivity of coxsackievirus type B and estimate daily and yearly risks of infection, morbidity, and mortality. The stability of coxsackievirus in the environment, its resistance to water treatment and its association with a range of serious illnesses underscore the importance of maintaining reliable and effective treatment of wastewater and drinking water. Additional research is needed on the occurrence of coxsackievirus in water supplies, with viral testing focusing on identification of specific viruses rather than viral groups. The resulting data will lead to a more complete database that can assist in the decision-making process for water treatment and watershed protection programs. - MPM.
• Nokes, R. L., Gerba, C. P., & Karpiscak, M. M. (2003). Microbial water quality improvement by small scale on-site subsurface wetland treatment. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 38(9), 1849-1855.
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  PMID: 12940486;Abstract: It has been demonstrated that large constructed wetlands used for domestic wastewater treatment are useful in the reduction of enteric microorganisms. This study evaluated the ability of three small-scale, on-site subsurface wetlands with different vegetation densities to remove total coliforms, fecal coliforms, coliphage, Giardia and Cryptosporidium. These wetlands were found to be equally efficient in the removal of enteric bacteria and coliphage as larger constructed wetlands. Giardia and Cryptosporidium were usually undetectable after passage of the wastewater through the subsurface wetlands. Coliphage removal increased with increasing vegetation density.
• Rusin, P., Bright, K., & Gerba, C. (2003). Rapid reduction of Legionella pneumophila on stainless steel with zeolite coatings containing silver and zinc ions. Letters in Applied Microbiology, 36(2), 69-72.
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  PMID: 12535123;Abstract: Aims: To determine the rate of reduction of Legionella pneumophila by stainless steel surfaces with zeolite ceramic coatings containing 2.5% (w/w) silver (Ag) and 14% zinc (Zn) ions. Methods and Results: Stainless steel pans with and without Ag/Zn coatings were inoculated with solutions of Leg. pneumophila ATCC 33155 and incubated at 37°C. Survival was monitored using the spread-plate technique on selective buffered charcoal yeast extract agar. Significant reductions of Leg. pneumophila were effected by the Ag/Zn zeolite coatings within 2 h of exposure. Conclusions, Significance and Impact of the Study: Zeolite ceramic Ag/Zn coatings impart significant anti-Legionella properties to stainless steel surfaces. Coated stainless steel could be used in the manufacture of air ducts, condensation pans and intake and exhaust vents. These products have the potential to reduce numbers of Legionella in air-handling systems.
• Thurston-Enriquez, J. A., Haas, C. N., Jacangelo, J., & Gerba, C. P. (2003). Chlorine inactivation of adenovirus type 40 and feline calicivirus. Applied and Environmental Microbiology, 69(7), 3979-3985.
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  PMID: 12839771;PMCID: PMC165174;Abstract: Ct values, the concentration of free chlorine multiplied by time of contact with virus, were determined for free-chlorine inactivation experiments carried out with chloroform-extracted (dispersed) and non-chloroform-extracted (aggregated) feline calicivirus (FCV), adenovirus type 40 (AD40), and polio virus type 1 (PV-1). Experiments were carried out with high and low pH and temperature conditions. Ct values were calculated directly from bench-scale free-chlorine inactivation experiments and from application of the efficiency factor Hom model. For each experimental condition, Ct values were higher at pH 8 than at pH 6, higher at 5°C than at 15°C, and higher for dispersed AD40 (dAD40) than for dispersed FCV (dFCV). dFCV and dAD40 were more sensitive to free chlorine than dispersed PV-1 (dPV-1). Cts for 2 log inactivation of aggregated FCV (aFCV) and aggregated PV-1 (aPV-1) were 31.0 and 2.8 orders of magnitude higher than those calculated from experiments carried out with dispersed virus. Cts for 2 log inactivation of dFCV and dAD40 in treated groundwater at 15°C were 1.2 and 13.7 times greater than in buffered-demand-free (BDF) water experiments at 5°C. Ct values listed in the U.S. Environmental Protection Agency (EPA) Guidance Manual were close to, or lower than, Ct values generated for experiments conducted with dispersed and aggregated viruses suspended in BDF water and for dispersed viruses suspended in treated groundwater. Since the state of viruses in water is most likely to be aggregated and associated with organic or inorganic matter, reevaluation of the EPA Guidance Manual Ct values is necessary, since they would not be useful for ensuring inactivation of viruses in these states. Under the tested conditions, dAD40, dFCV, aFCV, dPV-1, and aPV-1 particles would be inactivated by commonly used free chlorine concentrations (1 mg/liter) and contact times (60 to 237 min) applied for drinking water treatment in the United States.
• Thurston-Enriquez, J. A., Haas, C. N., Jacangelo, J., Riley, K., & Gerba, C. P. (2003). Inactivation of feline calicivirus and adenovirus type 40 by UV radiation. Applied and Environmental Microbiology, 69(1), 577-582.
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  PMID: 12514044;PMCID: PMC152434;Abstract: Little information regarding the effectiveness of UV radiation on the inactivation of caliciviruses and enteric adenoviruses is available. Analysis of human calicivirus resistance to disinfectants is hampered by the lack of animal or cell culture methods that can determine the viruses' infectivity. The inactivation kinetics of enteric adenovirus type 40 (AD40), coliphage MS-2, and feline calicivirus (FCV), closely related to the human caliciviruses based on nucleic acid organization and capsid architecture, were determined after exposure to low-pressure UV radiation in buffered demand-free (BDF) water at room temperature. In addition, UV disinfection experiments were also carried out in treated groundwater with FCV and AD40. AD40 was more resistant than either FCV or coliphage MS-2 in both BDF water and groundwater. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in BDF water were 109, 55, and 16 mJ/cm2, respectively. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in groundwater were slightly lower than those in BDF water. FCV was inactivated by 99% by 13 mJ/cm2 in treated groundwater. A dose of 103 mJ/cm2 was required for 99% inactivation of AD40 in treated groundwater. The results of this study indicate that if FCV is an adequate surrogate for human caliciviruses, then their inactivation by UV radiation is similar to those of other single-stranded RNA enteric viruses, such as poliovirus. In addition, AD40 appears to be more resistant to UV disinfection than previously reported.
• Vidales, J. A., Gerba, C. P., & Karpiscak, M. M. (2003). Virus removal from wastewater in a multispecies subsurface-flow constructed wetland. Water Environment Research, 75(3), 238-245.
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  PMID: 12837030;Abstract: Virus removal was studied in a multispecies subsurface-flow constructed wetland. Tracer studies and a virus survival test were conducted using bromide and bacteriophage PRD1 that were simultaneously added into a 6-year-old gravel-filled wetland. The estimated dimensionless variance and the observed bromide breakthrough curve suggest a plug-flow reactor with some dispersion. Most of the PRD1 was removed during the first 4 days; however, the PRD1 background concentration was not reached by the end of the study. Average bacteriophage removal was 98.8%, whereas bromide mass recovery was 75%. The removal rate of PRD1 was estimated to be -1.17 d -1; in contrast, its inactivation rate in situ for a 12.4-day period was -0.16 d -1. Apparently, virus removal is governed by an initial irreversible attachment followed by a comparatively long inactivation period. This study suggests that a subsurface-flow wetland can decrease the virus load by approximately 99% with a 5.5-day detention time.
• Bright, K. R., Gerba, C. P., & Rusin, P. A. (2002). Rapid reduction of Staphylococcus aureus populations on stainless steel surfaces by zeolite ceramic coatings containing silver and zinc ions. Journal of Hospital Infection, 52(4), 307-309.
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  PMID: 12473478;Abstract: This study demonstrates the anti- Staphylococcus aureus properties of stainless steel surfaces coated with zeolite containing 2.5% silver and 14% zinc ions. Stainless steel panels with and without the heavy-metal-containing coatings were inoculated with S. aureus and incubated at room temperature. Survival of S. aureus was significantly reduced by the silver/zinc coatings within 1 h. Many hospital surfaces could be constructed of stainless steel with silver/zinc zeolite coatings. Such measures may reduce rates of hospital-acquired S. aureus infection. © 2002 The Hospital Infection Society.
• Falabi, J. A., Gerba, C. P., & Karpiscak, M. M. (2002). Giardia and Cryptosporidium removal from waste-water by a duckweed (Lemna gibba L.) covered pond. Letters in Applied Microbiology, 34(5), 384-387.
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  PMID: 11967063;Abstract: Aims: To determine the ability of duckweed ponds used to treat domestic waste-water to remove Giardia and Cryptosporidium. Methods and Results: The influent and effluent of a pond covered with duckweed with a 6 day retention time was tested for Giardia cysts, Cryptosporidium oocysts, faecal coliforms and coliphage. Giardia cysts and Cryptosporidium oocysts were reduced by 98 and 89%, respectively, total coliforms by 61%, faecal coliforms by 62% and coliphage by 40%. There was a significant correlation between the removal of Giardia cysts and Cryptospordium oocysts by the pond (P < 0.001). Influent turbidity and parasite removal were also significantly correlated (Cryptosporidium and turbidity, P = 0.05; Giardia and turbidity, P = 0.01). Conclusions: The larger organisms (parasites) probably settled to the bottom of the pond, while removal of smaller bacteria and coliphages in the pond was not as effective. Significance and Impact of the Study: Duckweed ponds may play an important role in wetland systems for reduction of Giardia and Cryptosporidium.
• Gerba, C. P., Gramos, D. M., & Nwachuku, N. (2002). Comparative inactivation of enteroviruses and adenovirus 2 by UV light. Applied and Environmental Microbiology, 68(10), 5167-5169.
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  PMID: 12324370;PMCID: PMC126408;Abstract: The doses of UV irradiation necessary to inactivate selected enteric viruses on the U.S. Environmental Protection Agency Contaminant Candidate List were determined. Three-log reductions of echovirus 1, echo-virus 11, coxsackievirus B3, coxsackievirus B5, poliovirus 1, and human adenovirus type 2 were effected by doses of 25, 20.5, 24.5, 27, 23, and 119 mW/cm2, respectively. Human adenovirus type 2 is the most UV light-resistant enteric virus reported to date.
• Gerba, C. P., Perencevich, E., Wong, M. T., & Harris, A. (2002). Benefits of antibacterial products well documented [3] (multiple letters). American Journal of Infection Control, 30(4), 257-258.
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  PMID: 12032506;
• Gerba, C., Watt, P. M., Johnson, D. C., & Gerba, C. P. (2002). Improved method for concentration of Giardia, Cryptosporidium, and poliovirus from water. Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering, 37(3).
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  Methods for the concentration of enteric viruses and the protozoan parasites, Giardia and Cryptosporidium, from drinking water currently require the use of two different types of filters. Electropositive or electronegative microporous filters (0.2-0.45 microm nominal porosity) are used for the collection of enteroviruses, while polypropylene spun-fiber filters (1 microm porosity) and small pleated cartridge filters are used for the collection of protozoan parasites from water. Since the filter mechanically traps the protozoa by size exclusion, a microporous filter with an appropriately small nominal porosity could possibly be used for co-collection of both protozoa and enteroviruses. This study compared the concentration efficiencies of a polypropylene fiber cartridge (DPPPY) filter and two different microporous filters (Filterite and IMDS) with poliovirus (type 1), with respect to their ability to concentrate Giardia and Cryptosporidium from water. Giardia cysts and Cryptosporidium oocysts were added to 4001 of either tap water or tertiary treated wastewater and passed through the test filter. The protozoa were eluted from the polypropylene filter by hand-washing in a detergent solution. Viruses and protozoa were eluted from the microporous filter by two consecutive back-washes with a 1.5% beef extract, 0.1% Tween 80 solution. The eluent was then centrifuged to remove the parasites and the supernatant assayed for viruses. The overall efficiency was greater for the Filterite filter (40.4% for Giardia; 36.6% for Cryptosporidium) when compared to the spun fiber filter (10.1% for Giardia; 16.0% for Cryptosporidium). The Filterite filters were easier and faster to process than the polypropylene spun fiber filters. There was no significant difference in the recovery of protozoa from 1MDS and DPPPY filters. Co-collection of viruses and protozoan parasites from water onto the same filter is possible and can reduce the time and cost of routine water monitoring.
• Gibson, L. L., Rose, J. B., Haas, C. N., Gerba, C. P., & Rusin, P. A. (2002). Quantitative assessment of risk reduction from hand washing with antibacterial soaps. Journal of Applied Microbiology Symposium Supplement, 92(1), 136S-143S.
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  PMID: 12000622;Abstract: The Centers for Disease Control and Prevention have estimated that there are 3 713 000 cases of infectious disease associated with day care facilities each year. The objective of this study was to examine the risk reduction achieved from using different soap formulations after diaper changing using a microbial quantitative risk assessment approach. To achieve this, a probability of infection model and an exposure assessment based on micro-organism transfer were used to evaluate the efficacy of different soap formulations in reducing the probability of disease following hand contact with an enteric pathogen. Based on this model, it was determined that the probability of infection ranged from 24/100 to 91/100 for those changing diapers of babies with symptomatic shigellosis who used a control product (soap without an antibacterial ingredient), 22/100 to 91/100 for those who used an antibacterial soap (chlorohexadine 4%), and 15/100 to 90/100 for those who used a triclosan (1.5%) antibacterial soap. Those with asymptomatic shigellosis who used a non-antibacterial control soap had a risk between 49/1 000 00 and 53/100, those who used the 4% chlorohexadine-containing soap had a risk between 43/100 000 and 51/100, and for those who used a 1.5% triclosan soap had a risk between 21/100 000 and 43/100. The adequate washing of hands after diapering reduces risk and can be further reduced by a factor of 20% by the use of an antibacterial soap. Quantitative risk assessment is a valuable tool in the evaluation of household sanitizing agents and low risk outcomes.
• Gibson, L. L., Rose, J. B., Haas, C. N., Gerba, C. P., & Rusin, P. A. (2002). Quantitative assessment of risk reduction from hand washing with antibacterial soaps.. Symposium series (Society for Applied Microbiology), 136S-143S.
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  PMID: 12481838;Abstract: The Centers for Disease Control and Prevention have estimated that there are 3,713,000 cases of infectious disease associated with day care facilities each year. The objective of this study was to examine the risk reduction achieved from using different soap formulations after diaper changing using a microbial quantitative risk assessment approach. To achieve this, a probability of infection model and an exposure assessment based on micro-organism transfer were used to evaluate the efficacy of different soap formulations in reducing the probability of disease following hand contact with an enteric pathogen. Based on this model, it was determined that the probability of infection ranged from 24/100 to 91/100 for those changing diapers of babies with symptomatic shigellosis who used a control product (soap without an antibacterial ingredient), 22/100 to 91/100 for those who used an antibacterial soap (chlorohexadine 4%), and 15/100 to 90/100 for those who used a triclosan (1.5%) antibacterial soap. Those with asymptomatic shigellosis who used a non-antibacterial control soap had a risk between 49/100,000 and 53/100, those who used the 4% chlorohexadine-containing soap had a risk between 43/100,000 and 51/100, and for those who used a 1.5% triclosan soap had a risk between 21/100,000 and 43/100. The adequate washing of hands after diapering reduces risk and can be further reduced by a factor of 20% by the use of an antibacterial soap. Quantitative risk assessment is a valuable tool in the evaluation of household sanitizing agents and low risk outcomes.
• Hirotani, H., Naranjo, J., Moroyoqui, P. G., & Gerba, C. P. (2002). Demonstration of indicator microorganisms on surface of vegetables on the market in the United States and Mexico. Journal of Food Science, 67(5), 1847-1850.
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  Abstract: Presence of indicator microorganisms of fecal pollution on the surface of vegetables sold in retail markets is demonstrated. Vegetables were obtained from local markets in the U.S.A. and Mexico. At least 1 of the indicators, among coliphages, fecal streptococci, total coliforms, and fecal coliforms, was detected in every sample tested. Relatively small amounts of indicators were recovered from the U.S.A. samples. Fecal streptococci showed significant correlations with all other indicators. However, some U.S.A. samples low in fecal streptococci were found to harbor certain levels of other indicators. Upon introduction of an indicator system to detect the fecal contamination of agriculture crops, it is recommended that multiple indicator microorganisms be measured.
• Rusin, P. A., Gerba, C. P., & Bright, K. R. (2002). Rapid reduction of Staphylococcus aureus populations on stainless steel surfaces by zeolite ceramic coatings containing silver and zinc ions. THE JOURNAL OF HOSPITAL INFECTION, 52(4), 307-9. doi:https://doi.org/10.1053/jhin.2002.1317
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  This study demonstrates the anti-Staphylococcus aureus properties of stainless steel surfaces coated with zeolite containing 2.5% silver and 14% zinc ions. Stainless steel panels with and without the heavy-metal-containing coatings were inoculated with S. aureus and incubated at room temperature. Survival of S. aureus was significantly reduced by the silver/zinc coatings within 1 h. Many hospital surfaces could be constructed of stainless steel with silver/zinc zeolite coatings. Such measures may reduce rates of hospital-acquired S. aureus infection.
• Rusin, P., Maxwell, S., & Gerba, C. (2002). Comparative surface-to-hand and fingertip-to-mouth transfer efficiency of gram-positive bacteria, gram-negative bacteria, and phage. Journal of Applied Microbiology, 93(4), 585-592.
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  PMID: 12234341;Abstract: Aims: To determine the transfer efficiency of micro-organisms from fomites to hands and the subsequent transfer from the fingertip to the lip. Methods and Results: Volunteers hands were sampled after the normal usage of fomites seeded with a pooled culture of a Gram-positive bacterium (Micrococcus luteus), a Gram-negative bacterium (Serratia rubidea) and phage PRD-1 (Period A). Activities included wringing out a dishcloth/sponge, turning on/off a kitchen faucet, cutting up a carrot, making hamburger patties, holding a phone receiver, and removing laundry from the washing machine. Transfer efficiencies were 38.47% to 65.80% and 27.59% to 40.03% for the phone receiver and faucet, respectively. Transfer efficiencies from porous fomites were
• Stewart, M. H., Yates, M. V., Anderson, M. A., Gerba, C. P., Rose, J. B., Leon, R. D., & Wolfe, R. L. (2002). Predicted public health consequences of body-contact recreation on a potable water reservoir. Journal / American Water Works Association, 94(5), 84-97.
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  Abstract: A modeling-based risk assessment study was performed to assess the potential public health consequences to downstream potable water users consuming water from a drinking water reservoir. The occurrence of high-loading pathogen events associated with body contact (BC) recreation was observed to increase the daily risk of waterborne illness to downstream consumer. Results showed a three time increase in the annual risk of waterborne illness despite conventional treatment.
• Watt, P. M., Johnson, D. C., & Gerba, C. P. (2002). Improved method for concentration of Giardia, Cryptosporidium, and poliovirus from water. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 37(3), 321-330.
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  PMID: 11929071;Abstract: Methods for the concentration of enteric viruses and the protozoan parasites, Giardia and Cryptosporidium, from drinking water currently require the use of two different types of filters. Electropositive or electronegative microporous filters (0.2-0.45 μm nominal porosity) are used for the collection of enteroviruses, while polypropylene spun-fiber filters (1 μm porosity) and small pleated cartridge filters are used for the collection of protozoan parasites from water. Since the filter mechanically traps the protozoa by size exclusion, a microporous filter with an appropriately small nominal porosity could possibly be used for co-collection of both protozoa and enteroviruses. This study compared the concentration efficiencies of a polypropylene fiber cartridge (DPPPY) filter and two different microporous filters (Filterite and 1MDS) with poliovirus (type 1), with respect to their ability to concentrate Giardia and Cryptosporidium from water. Giardia cysts and Cryptosporidium oocysts were added to 4001 of either tap water or tertiary treated wastewater and passed through the test filter. The protozoa were eluted from the polypropylene filter by hand-washing in a detergent solution. Viruses and protozoa were eluted from the microporous filter by two consecutive back-washes with a 1.5% beef extract, 0.1% Tween 80 solution. The eluent was then centrifuged to remove the parasites and the supernatant assayed for viruses. The overall efficiency was greater for the Filterite filter (40.4% for Giardia; 36.6% for Cryptosporidium) when compared to the spun fiber filter (10.1% for Giardia; 16.0% for Cryptosporidium). The Filterite filters were easier and faster to process than the polypropylene spun fiber filters. There was no significant difference in the recovery of protozoa from 1MDS and DPPPY filters. Co-collection of viruses and protozoan parasites from water onto the same filter is possible and can reduce the time and cost of routine water monitoring.
• Casanova, L. M., Gerba, C. P., & Karpiscak, M. (2001). Chemical and microbial characterization of household graywater. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 36(4), 395-401.
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  PMID: 11413826;Abstract: In arid areas, the search for efficient methods to conserve water is of paramount importance. One of the methods of water conservation available today is graywater recycling - the reuse of water from the sinks, showers, washing machine, and dishwasher in a home. The purpose of this project was to characterize the chemical and microbial quality of graywater from a single-family home with two adults. Water samples from a graywater holding tank were analyzed over a seven-month period for total coliforms, fecal coliforms, fecal streptococci, Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa), and coliphages. The pH, turbidity, biological oxygen demand (BOD), suspended solids (SS), electrical conductivity (EC), sulfates (SO4), and chlorides (Cl) were also measured. The mean numbers of total coliforms, fecal coliforms, fecal streptococci, and P. aeruginosa were 8.03 × 107, 5.63 × 105, 2.38 × 102, and 1.99 × 104 CFU/100 mL, respectively. S. aureus and coliphages were not detected. In the chemical analysis, mean values of 7.47 for pH, 43 nephelometric turbidity units (NTU) for turbidity, 64.85 mg/L for BOD, 35.09 mg/L for SS, 0.43 mS/cm for EC, 59.59 mg/L for SO4, and 20.54 mg/L for Cl were measured. These data were compared to data taken in 1986 and 1987, when two adults and one child lived in the household. Analysis showed no statistically significant difference in levels of total coliforms and suspended solids between the two data sets. There were statistically significant differences in levels of fecal coliforms, pH, turbidity, chlorides, sulfates, and BOD between the two households. Fecal coliforms, turbidity, and BOD were higher in the household with two adults and one child. Levels of Cl, SO4, and pH were higher in the household with two adults.
• Casanova, L. M., Little, V., Frye, R. J., & Gerba, C. P. (2001). A survey of the microbial quality of recycled household graywater. Journal of the American Water Resources Association, 37(5), 1313-1319.
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  Abstract: In arid regions where populations are expanding and water is scarce, people are searching for ways to conserve and reuse water. One way homeowners can conserve water is by recycling graywater - wastewater from household sinks, showers, bathtubs, and washing machines. Graywater is used mostly for landscape irrigation. Since graywater is wastewater, reusing it raises concerns about disease transmission, either by contact with the water or the irrigated soil. The purpose of this study was to assess how factors such as number and age of household occupants, types of graywater storage, and sources of graywater used affect the microbial quality of graywater and soil irrigated with graywater. Sampies were collected over twelve months from eleven Tucson, Arizona households recycling graywater. Samples of graywater, soil irrigated by graywater, and soil irrigated by potable water were collected. We found that graywater irrigation causes a statistically significant increase in levels of fecal coliforms in soil when compared to soil irrigated with potable water. Graywater from the kitchen sink significantly increases levels of these bacteria in water and soil. Children also cause a statistically significant increase in fecal coliform levels in graywater and soil, possibly introducing a small amount of additional risk in graywater reuse.
• De, M., Karpiscak, M. M., Ellman, E. D., & Gerba, C. P. (2001). Removal of pathogenic and indicator microorganisms by a constructed wetland receiving untreated domestic wastewater. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 36(7), 1311-1320.
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  PMID: 11545355;Abstract: Wetlands containing floating, emergent and submergent aquatic plants, and other water-tolerant species have been found to economically provide a mechanism of enhancing the quality of domestic wastewater. The use of constructed wetlands for the removal of indicator bacteria (total and fecal coliforms), coliphages, protozoan parasites (Giardia and Cryptosporidium) and enteric viruses was investigated. A pilot scale constructed wetland consisting of two cells, one planted with bulrush and the other unplanted bare sand, were used to compare their efficiency in removing pathogens from raw sewage. Overall more than 90 percent of all microorganisms studied were removed by either of the two systems with a 1 to 2 day retention time. Removal of all mentioned microorganisms was greater from the surface flow in the unplanted cell than in the planted cell, except for Giardia and Cryptosporidium, although the differences were not statistically significant. Enteric viruses, coliphages and indicator bacteria were found to penetrate 2 m below the surface, although concentrations were reduced by greater than 99 percent in both cells. Less virus penetration into the sand occurred in the planted wetland versus the unplanted wetland. Water temperature was found to be the most important factor in the removal of enteric bacteria and viruses, while turbidity reduction was related to Giardia removal. These results demonstrate that significant reductions of pathogenic microorganisms can occur in constructed wetlands receiving untreated domestic wastewater with only a 1-2 day retention time.
• Enriquez, C., Nwachuku, N., & Gerba, C. P. (2001). Direct exposure to animal enteric pathogens. Reviews on Environmental Health, 16(2), 117-131.
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  PMID: 11512628;Abstract: Humans have very close interactions with working, food-producing, and companion animals. According to the American Veterinary Medical Association, there are more than one hundred million cat and dog pets in the United States. Furthermore, non-traditional pets like reptiles and exotic birds are not unusual companion animals in households. In addition to sharing with animals our living and/or working space and time, we also share, unfortunately, many disease causing microorganisms. In the past few years, we have become aware that several enteric pathogens that were thought to be mostly restricted to animals are a major cause of human disease. Examples of such pathogens include the protozoan parasite Cryptosporidium parvum and bacteria such as Campylobacter spp. This review will examine the characteristics of zoonotic enteric pathogens including bacterial (Helicobacter spp., Campylobacter spp., Salmonella spp., and verotoxin-producing Escherichia coli); parasitic (Toxoplasma gondii, Giardia spp., Cryptosporidium spp.); and viral (rotavirus, norwalk-like virus, hepatitis E virus), and the status of our knowledge with regard to the impact of such pathogens on human health.
• Gerba, C. P. (2001). Application of quantitative risk assessment for formulating hygiene policy in the domestic setting. Journal of Infection, 43(1), 92-98.
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  PMID: 11597169;
• Karpiscak, M. M., Sanchez, L. R., Freitas, R. J., & Gerba, C. P. (2001). Removal of bacterial indicators and pathogens from dairy wastewater by a multi-component treatment system. Water Science and Technology, 44(11-12), 183-190.
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  PMID: 11804092;Abstract: Microbial removal by a multi-component treatment system for dairy and municipal wastewater is being studied in Arizona, USA. The system consists of paired solids separators, anaerobic lagoons, aerobic ponds and constructed wetlands cells. The organisms under study include: total coliform, fecal coliform, enterovirus, Listeria monocytogenes, Clostridium perfringens, coliphage, Giardia lamblia and Cryptosporidium parvum. Organism removal rates from dairy wastewater varied from 13.2 per cent for fecal coliform to 94.9 per cent for coliphage. It appears that the much higher turbidity of the dairy wastewater, nearly 1,300 NTU, decreased the treatment systems' ability to remove some microbial indicators and pathogens. Information from this study can be used to determine the adequacy of multi-component treatment systems for the control of wastewater-borne pathogens, both in municipal treatment systems as well as in confined animal feeding operations (CAFO). This information also can assist municipalities and the CAFO industry in the implementation of rational and efficient treatment strategies for appropriate reuse of wastewaters.
• Oron, G., Armon, R., Mandelbaum, R., Manor, Y., Campos, C., Gillerman, L., Salgot, M., Gerba, C., Klein, I., & Enriquez, C. (2001). Secondary wastewater disposal for crop irrigation with minimal risks. Water Science and Technology, 43(10), 139-146.
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  PMID: 11436773;Abstract: A critical objective for any wastewater reuse program is to close the gap between supply of and demand for water and to minimize health and environmental hazards. Thus, the effects of treated effluent on crops, soils and community health must be considered carefully. When applying wastewater to soil-plant systems, it is to be noted that the passage of water through the soil reduces considerably the number of microorganisms carried out by the reclaimed wastewater. Nevertheless, there is a need to study the real rate of organism decay subject to water quality, soil and vegetable characteristics, and irrigation method. The aim of this work is to determine the fate of the fecal coliforms, coliphages F+ and CN13, and helminth eggs survival during the application of reclaimed wastewater in a vineyard orchard near the City of Arad (Israel) via onsurface and subsurface drip irrigation systems. Wastewater obtained from a stabilization pond, and soil samples were tested and an important decrease of microorganisms was reached in both cases, with the better values obtained with the sub-surface drip irrigation system.
• Rusin, P., & Gerba, C. (2001). Association of chlorination and UV irradiation to increasing antibiotic resistance in bacteria. Reviews of Environmental Contamination and Toxicology, 171, 1-52.
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  Abstract: In spite of widespread concern, there is no evidence in the scientific literature that warrants concluding that the use of chlorine or UV irradiation in industry or in the home has resulted in the emergence of mutant bacterial populations resistant to these disinfectants. At working concentrations, these disinfectants remain highly effective. The use of chlorine continues to result in significant reductions of pathogens in industry and in the home. The appropriate use of UV irradiation still results in significant decreases of bacterial pathogens in both the water treatment and medical industries. In addition, neither chlorination nor UV disinfection has been shown to result in the emergence of significant antibioticresistant bacterial populations in the home or in industry. Disinfection practices that result in significant reductions of pathogenic microbial populations reduce the risk of disease and, hence, reduce reliance upon antibiotics. This effect is very important as the trend of increasing antibiotic resistance is thought to be due to the overuse of antibiotics in both human and animals as well as noncompliance by patients suffering from infectious diseases. Although both chlorine and UV light are quite efficacious, the mode(s) of action are quite different. Chlorine is a multitarget disinfectant that affects several cellular constituents. Hence, single mutations are unlikely to result in a significant increase in resistance in a microorganism. Tolerance to chlorine is usually mechanical in nature and has never been demonstrated to be transferred on a plasmid. UV radiation used for disinfection purposes is in the UV-C range, which damages cells primarily by causing the formation of pyrimidine dimers in DNA and RNA. Nature has been using both means of killing bacteria for millions of years. Chlorine as hypochlorous acid has been used for countless years by white blood cells for disinfection purposes. Although UV-C radiation does not reach the earth's surface, sunlight also owes part of its disinfecting power to the formation of pyrimidine dimers. Bacteria have been exposed to sunlight for millions of years but sunlight still has considerable disinfecting power. © Springer-Verlag 2001.
• Thurston, J. A., Gerba, C. P., Foster, K. E., & Karpiscak, M. M. (2001). Fate of indicator microorganisms, giardia and cryptosporidium in subsurface flow constructed wetlands. Water Research, 35(6), 1547-1551.
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  PMID: 11317902;Abstract: Limited information is available on the ability of subsurface flow wetlands to remove enteric pathogens. Two multi-species wetlands, one receiving secondary sewage effluent and the other potable (disinfected) groundwater were studied from February 1995 to August 1996, at the Pima County Constructed Ecosystems Research Facility in Tucson, Arizona. Each wetland had a retention time of approximately 4 days. The objectives of this study were (1) to evaluate the ability of multi-species subsurface wetlands to physically remove Giardia cysts; Cryptosporidium oocysts, total and fecal coliforms, and coliphages; and (2) to determine the likely impact of local wildlife on the occurrence of these indicators and pathogens. In the wetland receiving secondary sewage effluent, total coliforms were reduced by an average of 98.8% and fecal coliforms by 98.2%. Coliphage were reduced by an average of 95.2%. Both Giardia cysts and Cryptosporidium oocysts were reduced by an average of 87.8 and 64.2%, respectively. In the wetland receiving disinfected groundwater, an average of 1.3×102 total coliforms/100mL and 22.3 fecal coliforms/100mL were most likely contributed by both flora and fauna. No parasites or coliphages were detected. Copyright © 2001 Elsevier Science Ltd.
• Gerba, C. P. (2000). Assessment of enteric pathogen shedding by bathers during recreational activity and its impact on water quality. Quantitative Microbiology, 2(1), 55-68.
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  Abstract: An assessment was made to determine the potential loading of enteric pathogenic protozoa and viruses into drinking water supply reservoirs by body contact recreation. These and other organisms of fecal origin are shed from the body during bathing. A literature review was conducted on the concentration of selected enteric viruses and protozoa during infection, the incidence of these infections, and duration of excretion. In addition, from existing literature, the amount of fecal material released during bathing was estimated from the shedding of fecal coliforms by bathers. The mean amount of fecal material shed per bather was estimated at 0.14 gram. The concentration of protozoan parasites (Giardia or Cryptosporidium) in feces of infected persons can range from 105 to 107 per gram and enteric viruses (enteroviruses, adenoviruses, rotavirus) from 105 to 1012 per gram. From this information, the concentration of enteric pathogens, shed into the water, could be calculated for a group of bathers. This information can be used to model the impact of body contact recreation on water quality in reservoirs used for drinking water supplies. Such information is useful in assessing the required treatment of the water to meet water quality regulations.
• Gerba, C. P., & Naranjo, J. E. (2000). Microbiological water purification without the use of chemical disinfection. Wilderness and Environmental Medicine, 11(1), 12-16.
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  PMID: 10731901;Abstract: Objectives. - Point-of-use (POU) water treatment systems are self- contained units that can be used by recreational enthusiasts who normally obtain drinking water from untreated sources (ie, rivers, lakes, etc). Microbiological water purifier units are capable of removing all waterborne pathogens. The purpose of this study was to evaluate a new technology (Structured Matrix) capable of microbiologically purifying the water without the use of chemical disinfectants or an external power requirement. Methods. - Each of 3 identical portable water filtration units were evaluated for their ability to remove Klebsiella terrigena, poliovirus type 1, rotavirus SA-11, and Cryptosporidium parvum oocysts. Units were operated according to the manufacturer's instructions to process 378 L of water. Each unit was challenged with test organisms after 0, 94, 190, 227, 284, 340, and 378 L had passed through it. For the 227-L and 284-L challenges, a 'worst- case' water quality (4°C, pH 9, and turbidity 30 NTU) was used that contained 1500 mg/L dissolved solids and 10 mg/L humid acid. At 340-L and 378-L challenges, worst-case water quality was adjusted to pH 5.0. Units were tested after stagnation for 48 hours following passage of 190, 340, and 378 L of water. Results. - The geometric average removal exceeded 99.9999% for bacteria, 99.99% for viruses, and 99.9% for Cryptosporidium parvum oocysts. Conclusion. - These units comply with the criteria guidelines for microbial removal under the United States Environmental Protection Agency's 'Guide Standard and Protocol for Testing Microbiological Water Purifiers'.
• Haas, C. N., Thayyar-Madabusi, A., Rose, J. B., & Gerba, C. P. (2000). Development of a dose-response relationship for Escherichia coli O157:H7. International Journal of Food Microbiology, 56(2-3), 153-159.
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  PMID: 10857541;Abstract: E. coli O157:H7 is an emerging food and waterborne pathogen. The development of acceptable guidelines for exposure to this organism based on quantitative microbial risk assessment requires a dose response curve. In this study, a prior animal study was used to develop a dose response relationship. The data was adequately fit by the beta-Poisson dose response relationship. This relationship was validated with reference to two outbreaks of this organism. It was found that the low dose extrapolation of the animal data using the beta-Poisson relationship provided estimates of risk concordant with those noted in the outbreaks. The fitted dose response relationship in conjunction with population estimates of the prevalence of E. coli O157:H7 illness indicates that the overall exposure is quite low in the US. Copyright (C) 2000 Elsevier Science B.V.
• Abbaszadegan, M., Stewart, P., Gerba, C., & LeChevallier, M. (1999). Erratum: A strategy for detection of viruses in groundwater by PCR (Applied and Environmental Microbiology (1999) 65:2 (444-449)). Applied and Environmental Microbiology, 65(11), 5192-.
• Chaidez, C., Candil-Ruiz, A., & Gerba, C. P. (1999). Microbiological survey of private roof water tanks in Culiacan, Mexico. Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering, 34(10), 1967-1978.
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  Abstract: A survey was conducted in Culiacan, Mexico on the water quality of private roof water tanks (PRWT). Heterotrophic bacteria, total and fecal coliforms, Pseudomonas aeruginosa, enteroviruses, and protozoan parasites (Cryptosporidium oocysts and Giardia cyst) were enumerated in 25 PRWT samples. Physico-chemical parameters such as pH, temperature, turbidity, and residual chlorine were also examined. P. aeruginosa was found in 28% of the samples; 32% also contained total coliforms, and 20% Escherichia coli. Heterotrophic plate count (HPC) bacteria were found in all of the samples with concentrations between 102 and 105 CFU/mL. No enteroviruses or protozoan parasites were detected suggesting adequate protection from human or large animal contamination.
• Chaidez, C., Rusin, P., Naranjo, J., & Gerba, C. P. (1999). Microbiological quality of water vending machines. International Journal of Environmental Health Research, 9(3), 197-206.
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  Abstract: Consumption of water from vending machines has recently increased in the United States. However, studies describing the bacteriological quality of water from these machines are scarce. In this study, bacteriological analyses were performed on samples from 30 water vending machines (WVMs), three of which were sampled weekly for 3 weeks. Bacteriological analyses were also conducted on the nozzle dispensers and the drains of 15 WVMs. Heterotrophic bacteria, total and fecal coliforms, and Pseudomonas aeruginosa were enumerated. Physico-chemical parameters such as pH, temperature, turbidity and residual chlorine were also examined. P. aeruginosa was found in 23% of the water samples and coliform bacteria in 20%. Heterotrophic plate count (HPC) bacteria were found in all samples and 73% had numbers greater than 500 colony forming units (CFU) ml-1. The HPC bacteria ranged from 9 to 48,000 CFU per sampled area on the dispensing nozzle. Total coliforms and Escherichia coli were detected in the drain samples with HPC bacterial concentrations from 1000 to 56,000 CFU per sampled area. No significant correlations were found between the physico-chemical and bacteriological parameters.
• Gerba, C. P. (1999). Virus Survival and Transport in Groundwater. Journal of Industrial Microbiology and Biotechnology, 22(4-5), 535-539.
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  Abstract: Almost half of all documented outbreaks of water-borne disease in the United States result from contaminated groundwater. Many of these outbreaks are known to be caused by viral agents. An understanding of factors that control virus migration through subsurface soil systems is necessary for the management of septic tank and wastewater land-treatment systems. The effectiveness of virus removal during land application of wastes is determined by their survival in the subsurface and their retention by soil particles. Both survival and retention are largely determined by (1) climate; (2) nature of the soil; and (3) nature of the microorganisms. Climate influences subsurface temperature which is probably the single most important factor in survival of viruses. Viruses are removed from groundwater by adsorption which is controlled by various characteristics of soil and the type and strain of virus. Both electrostatic and hydrophobic effects are now believed to be involved in virus adsorption.
• Gerba, C. P., Thurston, J. A., Falabi, J. A., Watt, P. M., & Karpiscak, M. M. (1999). Optimization of artificial wetland design for removal of indicator microorganisms and pathogenic protozoa. Water Science and Technology, 40(4-5), 363-368.
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  Abstract: The enhancement of water quality by artificial wetland systems is increasingly being employed throughout the world. Three wetlands were studied in Tucson, AZ to evaluate their individual performance in the removal of indicator bacteria (coliforms), coliphage, and enteric pathogens (Giardia and Cryptosporidium). A duckweed-covered pond, a multi-species subsurface flow (SSF) and a multi-species surface flow (SF) wetland were studied. Removal of the larger microorganisms, Giardia and Cryptosporidium, was the greatest in the duckweed pond at 98 and 89 percent, respectively. The lowest removal occurred in the SF wetland, 73 percent for Giardia and 58 percent removal for Cryptosporidium. In contrast, the greatest removal of coliphage, total and fecal coliforms occurred in the SSF wetland, 95, 99, and 98 percent respectively, whereas the pond had the lowest removals (40, 62,and 61 percent, respectively). Sedimentation may be the primary removal mechanism within the duckweed pond since the removal was related to size, removal of the largest organisms being the greatest. However, the smaller microorganisms were removed more efficiently in the SSF wetland, which may be related to the large surface area available for adsorption and filtration. This study suggests that in order to achieve the highest treatment level of secondary unchlorinated wastewater, a combination of aquatic ponds and subsurface flow wetlands may be necessary.
• Governal, R. A., & Gerba, C. P. (1999). Removal of MS-2 and PRD-1 bacteriophages from an ultrapure water system. Journal of Industrial Microbiology and Biotechnology, 23(3), 166-172.
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  Abstract: Viruses must be removed from the ultrapure water environment, as they have the potential to deposit on microelectronic devices and generate killer defects. Controlled and well-defined challenges by MS-2 and PRD-1 bacteriophages were treated in a pilot-scale ultrapure water system using ultraviolet radiation (UV), ozone, mixed bed ion exchange adsorption, and reverse osmosis filtration technologies typical of those used in industrial systems. ApplyIng a first order kinetic model to the data generated rate constants for MS-2 removal by UV-185, 50 mg L-1 ozone, mixed bed ion exchange or reverse osmosis filtration of 15.5, 12.9, 3.9, and 10.4 min-1, respectively, and PRD-1 removal of 13.8, 15.5, 8.2, and 11.9 min-1, respectively. In all cases, removal of viruses by oxidative mechanisms such as ozone and UV were far superior to adsorption and filtration mechanisms. A theoretical viral population balance was generated to model the removal of the bacteriophages by these unit operations. This model relates the inlet time-dependent profile of viruses to the output, destruction, and accumulation profiles; it also relates these profiles to the unit operation's treatment mechanisms including oxidation, adsorption, and filtration. This model is the first step in generating a site-independent theoretical model to project the persistence of viruses in ultrapure water systems.
• Karpiscak, M. M., Freitas, R. J., Gerba, C. P., Sanchez, L. R., & Shamir, E. (1999). Management of dairy waste in the Sonoran desert using constructed wetland technology. Water Science and Technology, 40(3), 57-65.
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  Abstract: An integrated wastewater treatment facility, consisting of upper (solids separators, anaerobic lagoons, and aerobic ponds) and lower (wetland cells) subsystems, has been built to replace the lagoon at a dairy in Arizona, USA. The collection sump of the new waste treatment facility collects all dairy wastewater outflow. Wastewater is then pumped to solids separators, and flows by gravity to anaerobic ponds and aerobic ponds. The upper subsystem is expected to treat the water sufficiently so that the wetland cells may achieve further pollutant reductions. The lower subsystem, comprised of 8 surface wetland cells with an approximate surface area of 5000 m2, receives outflow from the ponds. The cells are planted with cattail (Typha domingensis), soft-stem bulrush (Scirpus validus), and reed (Phragmites australis). After treatment is completed via the lagoons and ponds followed by the wetland cells, the wastewater can be reused to flush barns or to irrigate crops. Performance of the overall system is evaluated by measuring physical, chemical and biological parameters in water samples taken from selected locations along the treatment system. Chemical parameters studied include biochemical oxygen demand, pH, total suspended solids, nitrogen species. Biological monitoring included coliforms (total and fecal) and Listeria monocytogenes.
• Abbaszadegan, M., Emami, B., Farid, R., & Gerba, C. (1998). Occurrence of viruses and protozoan parasites in surface, ground and treated water in the city of Mashhad, Iran. Medical Journal of the Islamic Republic of Iran, 12(1), 41-45.
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  Abstract: A research plan was developed to evaluate the occurrence of enteroviruses, giardia cysts and cryptosporidium oocysts in thirty-five different sites in the city of Mashhad, Iran. The occurrence of these pathogenic microorganisms was evaluated to investigate a possible health risk in the communities. For the detection of enteroviruses in water samples, the conventional method of cell culture, using Buffalo Green Monkey (BGM) cell line, was used. The minimum sample volume for viruses was 500 liters, collected using a positively charged MK cartridge filter, eluted with beef extract and concentrated by organic flocculation. The method of detection for cysts and oocysts relied on microscopic observation of water samples by the immunofluorescence assay (IFA). For this study, water samples were collected using a cartridge filter, eluted by washing the filter using a detergent-based medium, concentrated by centrifugation, clarified by a percoll-sucrose density gradient, stained by an indirect fluorescent antibody, and examined by epifluorescence microscopy. A total of seventy surface, ground or treated water samples were collected from 35 different sites in the metropolitan city of Mashhad. Thirty-five samples were assayed for the presence of enteroviruses by cell culture and 35 samples were assayed by IFA technique for the detection of cysts and oocysts. Two surface water samples tested positive for virus presence and three surface water samples tested positive for giardia cysts. Based on the results of this research project, no microbial contamination of finished water was documented, suggesting proper treatment of surface water at the time of sampling.
• Anderson, M. A., Stewart, M. H., Yates, M. V., & Gerba, C. P. (1998). Modeling the impact of body-contact recreation on pathogen concentrations in a source drinking water reservoir. Water Research, 32(11), 3293-3306.
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  Abstract: A modeling study was conducted to evaluate the impact of body-contact recreation (e.g., water skiing, jet skiing, swimming) on pathogen concentrations in a source drinking water reservoir under construction in eastern Riverside County in Southern California. A hybridized Monte Carlo-finite segment model was used to predict pathogen concentrations in the reservoir resulting from pathogen inputs associated with shed fecal material and accidental fecal releases (AFRs). Monte Carlo techniques were incorporated into the finite segment model to define characteristics about individual recreators which affect pathogen loading to the reservoir (e.g., infection, pathogen shedding rate, location). Results of simulations are provided in the form of cumulative distribution and probability density functions derived from uncertainty analyses. The model predicted considerable spatial and temporal variability in pathogen concentrations within the reservoir, with elevated levels of Cryptosporidium, rotavirus, and poliovirus in the epilimnion during periods of high recreational use. Predicted Giardia concentrations were lower than the other pathogens. Hypolimnetic concentrations of all pathogens were generally 1-3 orders of magnitude lower than the overlying epilimnetic concentrations. Model results also suggest that field sampling will underestimate the mean, range and variance of pathogen concentrations in the reservoir. The model was further modified to include a particle tracking scheme to allow for transport of aggregated fecal material. Results from simulations using this approach demonstrate a potential for high pathogen loads due to body-contact recreation periodically reaching treatment plants.
• Rusin, P., Orosz-Coughlin, P., & Gerba, C. (1998). Reduction of faecal coliform, coliform and heterotrophic plate count bacteria in the household kitchen and bathroom by disinfection with hypochlorite cleaners. Journal of Applied Microbiology, 85(5), 819-828.
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  PMID: 9830117;Abstract: Fourteen sites evenly divided between the household kitchen and bathroom were monitored on a weekly basis for numbers of faecal coliforms, total coliforms and heterotrophic plate count bacteria. The first 10 weeks comprised the control period, hypochlorite cleaning products were introduced into the household during the second 10 weeks, and a strict cleaning regimen using hypochlorite products was implemented during the last 10 weeks. The kitchen was more heavily contaminated than the bathroom, with the toilet seat being the least contaminated site. The highest concentrations of all three classes of bacteria were found on sites that were moist environments and/or were frequently touched; these included the sponge/dishcloth, the kitchen sink drain area, the bath sink drain area, and the kitchen faucet handle(s). The implementation of a cleaning regimen with common household hypochlorite products resulted in the significant reduction of all three classes of bacteria at these four sites and other household sites.
• Abbaszadegan, M., Hasan, M. N., Gerba, C. P., Roessler, P. F., Wilson, B. R., Kuennen, R., & Dellen, E. V. (1997). The disinfection efficacy of a point-of-use water treatment system against bacterial, viral and protozoan waterborne pathogens. Water Research, 31(3), 574-582.
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  Abstract: A point-of-use (POU) water treatment system (WTS), comprised of a pressed activated carbon block filter followed by an ultraviolet (UV) light reactor, was evaluated for microbial disinfection efficacy following the general guidelines of the United States Environmental Protection Agency Guide Standard and Protocol for Testing Microbiological Water Purifiers. The POU WTS was challenged against bacterial, viral and protozoan waterborne pathogens including Vibrio cholerae, Shigella dysenteriae serotype 2, Escherichia coli 0157:H7, Salmonella typhi, hepatitis A virus strain HM 175, poliovirus type 1 strain Lsc2ab, simian rotavirus SA11, Cryptosporidium parvum oocysts, Giardia lamblia cysts and coliphage MS2. The POU WTS was tested for the removal/inactivation of each challenge organism in separate 16- to 20-day test periods under various conditions of water quality, at the system's maximum recommended flow rate and at 70% of the lamps normal UV intensity. For each organism tested, microbial challenges were conducted over the course of the test period at 0, 50, 100 and 150% of the system manufacturer's rated water treatment capacity. Each microbial challenge consisted of 30 L of influent water containing approximately 105 bacterial cfu/mL, 104 viral pfu/mL or 103 protozoan cysts/mL. Inffluent and effluent water samples were taken during the challenges and assayed for the particular pathogen and the percent reduction calculated. Effluent water samples were also taken and assayed for the possible presence of the pathogens following two 60-h stagnation periods. The POU WTS was found to effectively remove and/or inactivate greater than 99.9999% of the bacterial pathogens, greater than 99.99% of the viruses and greater than 99.9% of the protozoan cysts and oocysts tested to 150% of the water treatment capacity of the POU WTS. These findings suggest that a properly designed and operated POU WTS may be a practical approach to removing microbiological waterborne pathogens from drinking water.
• Asthana, S., Rusin, P., & Gerba, C. P. (1997). Influence of hydrocarbons on the virulence and antibiotic sensitivity associated with Pseudomonas aeruginosa. International Journal of Environmental Health Research, 7(4), 277-287.
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  Abstract: The bacterium, Pseudomonas aeruginosa has the potential for use in bioremediation. However, this organism is an opportunistic pathogen and is highly resistant to disinfectants and antibiotics. P. aeruginosa has been known to cause a wide variety of infections in humans, especially in immunocompromised persons. The purpose of this study was to assess the influence of hydrocarbons on the virulence of P. aeruginosa as it degrades these hydrocarbons. The expression of virulence factors associated with 12 different hydrocarbon-degrading strains of P. aeruginosa was evaluated. Virulence factors including hemolytic activity, antibiotic sensitivity, cell adherence, and exopolysaccharide capsule formation were tested in the presence of 0.1% glucose and the appropriate hydrocarbon. No differences were found in hemolytic activity or antibiotic resistance in the presence of glucose or hydrocarbon. Growth on glucose significantly enhanced adherence, while growth on a hydrocarbon enhanced capsule formation. The results of this study indicate that, overall, growth in the presence of hydrocarbons such as hexadecane does not enhance the virulence characteristics of P. aeruginosa.
• Crabtree, K. D., Gerba, C. P., Rose, J. B., & Haas, C. N. (1997). Waterborne adenovirus: A risk assessment. Water Science and Technology, 35(11-12), 1-6.
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  Abstract: Adenoviruses have been detected in raw sewage throughout the world and are associated with a number of human illnesses but their occurrence and pathogenicity have not been well studied. A risk assessment approach was used to determine their significance as a waterborne pathogen. There are 47 types of adenoviruses and the diseases resulting from infections include conjunctivitis, pharyngitis, pneumonia; acute and chronic appendicitis, exanthematous disease, bronchiolitis, acute respiratory disease, and gastroenteritis (types 40 and 41). Adenovirus is considered to be only second to rotavirus in terms of its significance as a pathogen of childhood gastroenteritis. Adenovirus infections are usually acute and self-limiting with a greater severity of illness occurring in the immunocompromised (e.g. AIDS patients and transplant recipients). They are reported to be more resistant to inactivation by UV than enteroviruses and are sometimes detected at higher levels in polluted waters. There are documented outbreaks of conjunctivitis due to adenovirus types 3 and 4 associated with swimming in contaminated recreational waters. Based on the data obtained from human dose-response studies, the exponential model [P(i)= 1 -exp(-rN); r = 0.4172] was chosen for this risk assessment. Annual risks of infection in drinking water for adenovirus at average levels of 1/1000L to 1/100L ranged from 8.3/10,000 to 8.3/1000, respectively. Using monitoring data from a recreational water, risks were calculated to be as high as 1/1000 for a single exposure.
• Gerba, C. P., Johnson, D. C., & Hasan, M. N. (1997). Efficacy of iodine water purification tablets against Cryptosporidium oocysts and Giardia cysts. Wilderness and Environmental Medicine, 8(2), 96-100.
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  PMID: 11990150;Abstract: The ability to control water-borne diseases is critical for soldiers, hikers, and others who may need to drink directly from an outdoor source. Water-borne protozoan parasites that are specifically of concern are Giardia and Cryptosporidium because of their resistance to halogen disinfection. The purpose of this study was to determine the effectiveness of iodine tablets against Giardia and Cryptosporidium under general- and worst-case water conditions that might be found in the field. Giardia cysts and Cryptosporidium oocysts were exposed to iodine according to manufacturer's instructions (two tablets/L = 13-18 mg/L for 20 minutes). This dose inactivated 3-log10 of Giardia in general-case water and pH 9. In worst-case water, however, only about 35% of cysts were inactivated at pH 5. Fifty minutes were required to achieve a 3-log10 reduction at pH 5. Cryptosporidium oocysts were more difficult to inactivate. Only 10% were inactivated after a 20-minute exposure to iodine according to manufacturer's instructions; even after 240 minutes of exposure to iodine only 66-81% oocysts were inactivated. These data strongly suggest that iodine disinfection is not effective in inactivating Cryptosporidium oocysts in water. Because this organism is common in all surface waters, it is recommended that another method of treatment be used before ingestion.
• Gerba, C. P., Naranjo, J. E., & Hansan, M. N. (1997). Evaluation of a combined portable reverse osmosis and iodine resin drinking water treatment system for control of enteric waterborne pathogens. Journal of Environmental Science and Health - Part A Environmental Science and Engineering and Toxic and Hazardous Substance Control, 32(8), 2337-2354.
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  Abstract: Three identical portable reverse osmosis-iodine resin drinking water treatment systems were evaluated for their ability to inactivate/remove Klebsiella terrigena, poliovirus type 1. rotavirus SA-11. and Cryptosporidium oocysts. The units were operated according in the manufacture's instructions for 500 hours of operation. The units were challenged with the test microorganisms after 0. 125, 250, 300, 375, 450, and 500 hours of operation. Worst case water quality challenges were done at the 60% (300 hours) and 75% (375 hours), lifetime challenge. This 'worst case' consisted of 1500 mg/l dissolved solids, 10 mg/l organic matter, a turbidity of 30 NTU, and a pH of 9.0 at 4°C. At the 90% (450 hours) and 100% (500 hours) lifetime test the 'worst case' water quality adjusted to pH 5.0 was used. The units were also tested after stagnation for 48 hours at 50%, 75%, and 100% lifetime challenges. The geometric average removals exceeded 99.9999% for the bacteria, 99.99% for the viruses, and 99.9% for the Cryptosporidium oocysts. However, on occasion, all test organisms were observed in the reverse osmosis (RO) permeate, especially when low turbidity water was processed. This demonstrated that the small rated pore size of RO membrane cannot be relied upon as an absolute guarantee of complete microorganism removal. The iodine provided additional assurance of microbial inactivation and prevention of colonization by pathogenic bacteria. The results indicate that these portable units would comply with the criteria guidelines for microbial removals under the U.S. Environmental Protection Agency's Guide Standard and Protocol for Testing Microbiological Water Purifiers.
• Governal, R. A., & Gerba, C. P. (1997). Persistence of MS-2 and PRD- 1 bacteriophages in an ultrapure water system. Journal of Industrial Microbiology and Biotechnology, 18(5), 297-301.
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  PMID: 9218359;Abstract: The persistence of bacteriophages MS-2 and PRD-1 was evaluated in tap water, in reverse osmosis (RO) permeate, and in three locations within an ultrapure water system; ultrapure samples included pre- and post-UV sterilization and post-mixed bed ion exchange tank. The inactivation rates for MS-2 were calculated as log10 reduction per hour and per day: k= - (log10 C(t)C(o))/t. PRD-1 was found to persist with no significant loss of infectivity in all water purity environments evaluated. Inactivation of MS-2 was dependent on water quality and pH. Short-term inactivation rates for chlorinated tap water, post-RO, pre-UV, post-UV and post-ion exchange sample locations were 0.028, 0.455, 0.231, 0.191 and 0.168 log10 h-1, respectively. Long-term inactivation rates for chlorinated tap water, post-RO, pre-UV, post-UV and post-ion exchange sample locations were 0.485, 0.911, 0.605, 0.632 and 0.684 log10 day-1, respectively. Since phages were found to remain intact as well as to lyse in the ultrapure water environment, the phages have the potential to contaminate the ultrapure water environments of the microelectronics, pharmaceutical and power generation industries in both colloidal and dissolved form. Further work is proceeding to generate standardized and cost-effective methods to detect viruses in water environments.
• Haas, C. N., Rose, J. B., Gerba, C. P., & Crockett, C. S. (1997). What predictive food microbiology can learn from water microbiology. Food Technology, 51(4), 91-94.
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  Abstract: Methods used for the assessment and control of microbial risks from drinking water can be applied to food risks as well, but a substantial database is needed.
• Naranjo, J. E., Chaidez, C., Quiñonez, M., Gerba, C. P., Olson, J., & Dekko, J. (1997). Evaluation of a portable water purification system for the removal of enteric pathogens. Water Science and Technology, 35(11-12), 55-58.
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  Abstract: The need for personal and potable water treatment devices has evolved from consumer interest in improving and ensuring the quality of drinking water. Such devices are especially useful to hikers and campers who often must use available surface water supplies. A portable iodinated water purification system was evaluated for the ability to inactivate/remove Klebsiella terrigena, poliovirus type 1, rotavirus SA-11 and Cryptosporidium oocysts under a variety of different water quality conditions:
• Rusin, P. A., Rose, J. B., & Gerba, C. P. (1997). Health significance of pigmented bacteria in drinking water. Water Science and Technology, 35(11-12), 21-27.
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  Abstract: The purpose of this study was to determine the relative health risks of pigmented bacteria found in drinking water samples. These pigmented bacteria include opportunistic pathogens such as Flavobacterium, Pseudomonas, Corynebacterium, Nocardia, Mycobacterium, Erwinia, Enterobacter, Serratia, and Micrococcus. Flavobacterium, meningosepticum is the most clinically important of the flavobacteria but causes < 0.08% of meningitis cases in the US. Pseudomonas aeruginosa is an important opportunistic pathogen causing > 10% of nosocomial infections. Human feeding tests show that oral doses of 106 to 108 CFU results in colonisation of the gastrointestinal (GI) tract but do not produce any morbidity in healthy volunteers. Corynebacteria rarely cause disease except for toxigenic C. diphtheriae which is non-pigmented on R2A agar. The most important member of Nocardia is N. asteroides which is an opportunistic pathogen for certain immunocompromised population segments. National surveys show that only 9.2-19.2% of mycobacterial clinical isolates are pigmented with M. kansasii being the most frequent (4-10%). This bacterium is associated with disease but would not be detected as part of the HPC bacteria using a 7d incubation period. Pigmented strains of Erwinia, Enterobacter, Serratia, and Micrococcus can cause disease but they are relatively unimportant compared to other pathogenic bacteria as shown in ranking studies.
• Rusin, P. A., Rose, J. B., Haas, C. N., & Gerba, C. P. (1997). Risk assessment of opportunistic bacterial pathogens in drinking water.. Reviews of environmental contamination and toxicology, 152, 57-83.
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  PMID: 9297985;Abstract: This study was undertaken to examine quantitatively the risks to human health posed by heterotrophic plate count (HPC) bacteria found naturally in ambient and potable waters. There is no clear-cut evidence that the HPC bacteria as a whole pose a public health risk. Only certain members are opportunistic pathogens. Using the four-tiered approach for risk assessment from the National Academy of Sciences, hazard identification, dose-response modeling, and exposure through ingestion of drinking water were evaluated to develop a risk characterization, which estimates the probability of infection for individuals consuming various levels of specific HPC bacteria. HPC bacteria in drinking water often include isolates from the following genera: Pseudomonas, Acinetobacter, Moraxella, Aeromonas, and Xanthomonas. Other bacteria that are commonly found are Legionella and Mycobacterium. All these genera contain species that are opportunistic pathogens which may cause serious diseases. For example, the three nonfermentative gram-negative rods most frequently isolated in the clinical laboratory are (1) Pseudomonas aeruginosa, (2) Acinetobacter, and (3) Xanthomonas maltophilia. P. aeruginosa is a major cause of hospital-acquired infections with a high mortality rate. Aeromonas is sometimes associated with wound infections and suspected to be a causative agent of diarrhea. Legionella pneumophila causes 4%-20% of cases of community-acquired pneumonia and has been ranked as the second or third most frequent cause of pneumonia requiring hospitalization. The number of cases of pulmonary disease associated with Mycobacterium avian is rapidly increasing and is approaching the incidence of M. tuberculosis in some areas. Moraxella can cause infections of the eye and upper respiratory tract. The oral infectious doses are as follows in animal and human test subjects: P. aeruginosa, 10(8)-10(9); A, hydrophila, > 10(10); M. avium, 10(4)-10(7); and X. maltophilia, 10(6)-10(9). The infectious dose for an opportunistic pathogen is lower for immunocompromised subjects or those on antibiotic treatment. These bacteria have been found in drinking water at the following frequencies: P. aeruginosa, < 1%-24%; Acinetobacter, 5%-38%; X. maltophilia, < 1%-2%; Aeromonas, 1%-27%; Moraxella, 10%-80%; M. avium, < 1%-50%; and L. pneumophila, 3%-33%. These data suggest that drinking water could be a source of infection for some of these bacteria. The risk characterization showed that risks of infection from oral ingestion ranged from a low of 7.3 x 10(-9) (7.3/billion) for low exposures to Aeromonas to higher risks predicted at high levels of exposure to Pseudomonas of 9 x 10(-2) (98/100). This higher risk was only predicted for individuals on antibiotics. Overall, the evidence suggests that specific members of HPC bacteria found in drinking water may be causative agents of both hospital- and community-acquired infections. However, the case numbers may be very low and the risks represent levels generally less than 1/10,000 for a single exposure to the bacterial agent. Future research needs include (1) determining the seasonal concentrations of these bacteria in drinking water, (2) conducting adequate dose-response studies in animal subjects or human volunteers, (3) determining the health risks for an individual with multiple exposures to the opportunistic pathogens, and (4) evaluating the increase in host susceptibility conferred by antibiotic use or immunosuppression.
• Brown, R., Craun, G., Dufour, A., Eisenberg, J., Foran, J., Gauntt, C., Gerba, C., Haas, C., Highsmith, A., Irbe, R., Julkunen, P., Juranek, D., LeChevallier, M., Levine, M., Macler, B., Murphy, P., Payment, P., Pfaender, F., Regli, S., , Roberson, A., et al. (1996). A conceptual framework to assess the risks of human disease following exposure to pathogens. Risk Analysis, 16(6), 841-848.
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  PMID: 8972112;Abstract: Currently, risk assessments of the potential human health effects associated with exposure to pathogens are utilizing the conceptual framework that was developed to assess risks associated with chemical exposures. However, the applicability of the chemical framework is problematic due to many issues that are unique to assessing risks associated with pathogens. These include, but are not limited to, an assessment of pathogen/host interactions, consideration of secondary spread, consideration of short- and long-term immunity, and an assessment of conditions that allow the microorganism to propagate. To address this concern, a working group was convened to develop a conceptual framework to assess the risks of human disease associated with exposure to pathogenic microorganisms. The framework that was developed consists of three phases: problem formulation, analysis (which includes characterization of exposure and human health effects), and risk characterization. The framework emphasizes the dynamic and iterative nature of the risk assessment process, and allows wide latitude for planning and conducting risk assessments in diverse situations, each based on the common principles discussed in the framework.
• Crockett, C. S., Haas, C. N., Fazil, A., Rose, J. B., & Gerba, C. P. (1996). Prevalence of shigellosis: In the U.S. consistency with dose-response information. International Journal of Food Microbiology, 30(1-2), 87-99.
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  PMID: 8856376;Abstract: Every year there are estimated 300 000 cases of Shigella in the United States. A beta-poisson model was fit to human dose-response information ion pathogenic Shigella using the Maximum Likelihood Estimation technique. Pooled and separate data sets for the Shigella species were fit to the beta-Poisson model and 95% confidence limits and regions were calculated. Shigella dysentariae and Shigella flexneri confidence regions and limits overlapped with each other and with the pooled data set, suggesting that this model can describe Shigella in general. The pooled Shigella model as well as the upper and lower confidence limits of the three data sets showed average exposures based on the estimated U.S. caseload of pathogenic Shigella of 0.01 to 0.014 organisms (confidence limits 0.001-0.05) for a 7-day per annum period of exposure and ranges from 0.07 to 0.1 organisms (confidence limits 0.006-0.4). for a 1-day per annum period of exposure. The plausibility of the pooled dose-response model was then evaluated by comparison with two known-cruise ship outbreaks. The pooled model estimated that the two outbreaks studied could have been due to ingestion of 344 (confidence limits 72-915) Shigella cells per meal and 10.5-12 (confidence limits 1-44) Shigella cells per glass of water by passengers.
• Gerba, C. P., Rose, J. B., & Haas, C. N. (1996). Sensitive populations: Who is at the greatest risk?. International Journal of Food Microbiology, 30(1-2), 113-123.
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  PMID: 8856378;Abstract: The purpose of this article was to review the existing literature to define those groups of individuals who would be at the greatest risk of serious illness and mortality from water and foodborne enteric microorganisms. This group was found to include the very young, the elderly, pregnant women, and the immunocompromised. This segment of the population currently represents almost 20% of the population in the United States and is expected to increase significantly by the beginning of the next century, because of increases in life-span and the number of immunocompromised individuals. More than half of documented deaths from gastroenteritis and hepatitis A illness occur in the elderly in developed countries. The overall case fatality ratio for foodborne bacterial gastroenteritis outbreaks in nursing homes is 10 times greater than the general population. Pregnant mothers suffer from a case fatality ratio from hepatitis E infections ten times greater than the general population during waterborne disease outbreaks. Enteric diseases are most common and devastating among the immunocompromised. Cryptosporidium is a serious problem among patients with acquired immuno-deficiency syndrome (AIDS). Cancer patients undergoing chemotherapy and transplant patients, are also at significantly greater risk of dying from enteric viral infections than the general population. This review indicates the need for consideration of enhanced protection for certain segments of the population who will suffer the most from food and waterborne pathogens.
• Gerba, C. P., Rose, J. B., Haas, C. N., & Crabtree, K. D. (1996). Waterborne rotavirus: A risk assessment. Water Research, 30(12), 2929-2940.
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  Abstract: A risk assessment approach was used to estimate the public health impacts from exposure to human rotavirus in drinking and recreational waters. Rotavirus is the major cause of viral gastroenteritis worldwide and several waterborne outbreaks have been documented. This results in a significant economic impact on society in terms of direct medical costs, loss of work, quality of life and mortality. The virus is common in domestic wastewater and polluted surface waters. Dose-response data in human adult volunteers indicate that it is the most infective of all the enteric viruses, and this was used to develop a microbial risk assessment model to estimate daily and yearly risks of infection, morbidity and mortality for exposure via drinking and recreational waters using existing information on the occurrence of rotavirus. The disease is most severe for the very young, the elderly, and the immunocompromised. Case fatality rates in the United States are 0.01% in the general population, 1% in the elderly, and up to 50% in the immunocompromised. Analysis indicates that significant risks of disease (5 x 10-1-2.45 x 10-3)) could result for drinking and recreational waters in which rotavirus has been detected. The major limitation in assessing the risks of waterborne rotaviral infections at present is the lack of data on its occurrence in water and the potential for human exposure.
• Haas, C. N., Crockett, C. S., Rose, J. B., Gerba, C. P., & Fazil, A. M. (1996). Assessing the rick posed by oocysts in drinking water. Journal / American Water Works Association, 88(9), 131-136.
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  Abstract: A recent study of infection and illness in human volunteers subjected to controlled exposure to oocysts of Cryptosporidium parvum provided a suitable data base for dose-response analysis. The authors analyzed the study data, and using exponential and beta-poisson dose-response models, arrived at an estimate of the waterborne concentrations associated with various risk levels.
• Hinsby, K., McKay, L. D., Jørgensen, P., Lenczewski, M., & Gerba, C. P. (1996). Fracture Aperture Measurements and Migration of Solutes, Viruses, and Immiscible Creosote in a Column of Clay-Rich Till. Ground Water, 34(6), 1065-1075.
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  Abstract: A series of ground-water flow and tracer experiments were performed on an undisturbed column of fractured clay-rich till, 0.5 m diameter by 0.5 m long, in a pressure-controlled cell. The measured hydraulic conductivity of the sample was 1.0 to 1.2 × 10-6 m/sec and the average hydraulic gradient during the tracer experiments ranged from 0.45 to 0.49. The experiments clearly show that ground-water flow and contaminant migration through the sample is primarily controlled by fractures and root holes. Tracer experiments using a solute (chloride), colloid-sized bacteriophage (PRD-1 and MS-2) and uncharged latex microspheres, indicated very fast transport rates of 4 to 360 m/day. These rates are similar to fracture flow velocities calculated on the basis of the measured bulk hydraulic conductivity of the column, and measured fracture spacing, using the cubic law for flow through parallel-walled fractures. Fracture aperture values calculated from the ground-water flow data (35 to 56 μm) are of the same magnitude as values calculated from the breakthrough of tracers (13 to 120 μm). Aperture values calculated for fractures (1 to 94 μm) and root holes (2 to 188 μm), on the basis of measured immiscible creosote entry pressures, are also comparable with these values. The injected creosote, a DNAPL, penetrated most of the visible and a few invisible fractures and root holes, indicating that, for this till, fractures and root holes are important conduits for the transport of DNAPL's.
• Karpiscak, M. M., Gerba, C. P., Watt, P. M., Foster, K. E., & Falabi, J. A. (1996). Multi-species plant systems for wastewater quality improvements and habitat enhancement. Water Science and Technology, 33(10-11), 231-236.
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  Abstract: The use of macrophytic plants for the treatment of municipal wastewater is growing rapidly. The Constructed Ecosystems Research Facility (CERF) is a joint project of the Pima County Wastewater Management Department and The University of Arizona's Office of Arid Lands Studies. The facility consists of five 30-mil-hyperlon-lined raceways measuring 61 m long, 8.2 m wide, and 1.4 m deep and one slightly larger raceway. Research has been and is being conducted with aquatic plants such as water hyacinth (Eichhornia crassipes), duckweed (Lemna spp.), giant reed (Arundo donax), bulrush (Scirpus olneyi), black willow (Salix nigra), and cottonwood (Populus fremontii). Composite water samplers are used to collect refrigerated samples from incoming secondary wastewater from Pima County's Sewage Treatment Facility and from the effluent leaving each raceway. Water samples have been analyzed for parameters such as pH, RODS, and total nitrogen. Microbiological studies have concentrated on the removal of indicator coliform bacteria, as well as Giardia, Cryptosporidium and viruses from the wastewater. Data from the water quality studies indicate that these constructed ecosystems reduce BOD5 consistently to below the 10 mg/L BOD5, tertiary standard, remove nitrogen as well as decrease the concentration of pathogens significantly.
• Meng, Q. S., & Gerba, C. P. (1996). Comparative inactivation of enteric adenoviruses, poliovirus and coliphages by ultraviolet irradiation. Water Research, 30(11), 2665-2668.
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  Abstract: The inactivation of enteric adenoviruses 40 and 41 by ultraviolet (UV) radiation was investigated and compared with poliovirus type 1 (strain LSc-2ab) and coliphages MS-2 and PRD-1. Purified stocks of the viruses were exposed to collimated ultraviolet radiation in a stirred reactor for a total dose of up to 140 mW s/cm2. The doses of UV to achieve a 90% inactivation of adenovirus 40, adenovirus 41, coliphages MS-2 and PRD-1 and poliovirus type 1 were 30, 23.6, 14, 8.7 and 4.1 mW s/cm2, respectively. Adenovirus 40 was significantly more resistant than coliphage MS-2 to UV irradiation (P < 0.01). Adenovirus 41 appeared slightly more sensitive than adenovirus 40, but the difference was not significant (P > 0.05). The resistance of PRD-1 was less than MS-2 (P < 0.01), but greater than poliovirus type 1 (P < 0.01). Adenoviruses 40 and 41 were more resistant than Bacillus subtilis spores, often suggested as an indicator of UV light performance. The double-stranded DNA adenoviruses appear to be the most resistant of all potentially water-borne enteric viruses to UV light disinfection.
• Cassells, J. M., Yahya, M. T., Gerba, C. P., & Rose, J. B. (1995). Efficacy of a combined system of copper and silver and free chlorine for inactivation of Naegleria fowleri amoebas in water. Water Science and Technology, 31(5-6), 119-122.
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  Abstract: Electrolytically generated copper and silver ions (400:40 and 800:80 μg/l) were evaluated separately and combined with 1.0 mg/l free chlorine, for their efficacy in reducing the viable numbers of Naegleria fowleri amoebas in water (pH 7.3 and 23-250C). Inactivation rates (k = log10 reduction/min) and T99 values (exposure time required to achieve a 99% or a 2 log10 reduction) of the disinfectants were determined. Copper and silver alone, at ratio of 400:40 to 800:80 μg/l caused no significant inactivation of N. fowleri even after 72 hours of exposure (k = 0.00017 and 0.00013, respectively). Addition of 1.0 mg/l free chlorine to water which contained 400:40 or 800:80 μg/l copper and silver resulted in enhanced inactivation rates (k = 0.458 and 0.515, respectively) compared to either chlorine alone (k = 0.33) or the metals alone. Water containing 800:80 μg/l copper and silver with 1.0 mg/l chlorine showed a T99 value of 3.9 minutes, while chlorine alone showed a T99 of 6.1 minutes. Enhanced inactivation of N. fowleri by a combined system of free chlorine and copper and silver may be attributed to the different mechanism that each disinfectant utilizes in inactivating the amoebas, and may suggest a synergistic effect.
• Enriquez, C. E., & Gerba, C. P. (1995). Concentration of enteric adenovirus 40 from tap, sea and waste water. Water Research, 29(11), 2554-2560.
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  Abstract: The enteric adenovirus types 40 (Ead 40) and 41 (Ead 41) are the second most common cause of viral gastroenteritis in children. Since their occurrence in the aquatic environment is unknown, their role as waterborne pathogens has not been determined. This study evaluated the ability of electronegative microporous filters to recover Ead 40 from tap water, secondary treated sewage, and artificial and natural sea waters, and the ability of electropositive microporous filters to recover Ead 40 from tap water. The efficiency of organic flocculation and PEG precipitation to reconcentrate Ead 40 from beef extract eluents was also assessed. Viral assays were conducted by the TCID50 method in PLC/PRF/5 cells. With electronegative filters, recovery efficiencies of 36, 38, and 22% were obtained from 113-1. volumes of tap, sea water, and secondary sewage, respectively, using electropositive filters Ead 40 was recovered from tap water, with an efficiency of 26.5%. No significant difference was observed, by paired t-test analysis, when comparing the concentration efficiencies between organic flocculation (38.6%), and PEG precipitation (40%). These results show that Ead 40 can be concentrated from water samples, with efficiencies comparable to other enteric viruses. © 1995.
• Enriquez, C. E., Hurst, C. J., & Gerba, C. P. (1995). Survival of the enteric adenoviruses 40 and 41 in tap, sea, and waste water. Water Research, 29(11), 2548-2553.
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  Abstract: The enteric adenoviruses types 40 (Ead 40) and 41 (Ead 41) have emerged as a leading cause of viral gastroenteritis in children, second in importance only to the rotaviruses. The role of the enteric adenoviruses as waterborne pathogens has not been evaluated. This study compared the survival of these agents with poliovirus type 1 (polio 1) and the hepatitis A virus (HAV) in tap water at 4°C, and at room temperature, with polio 1 in primary and secondary wastewater at 4, and 15°C, and in sea water at 15°C. Assays were conducted at regular intervals by the TCID50 method in PLC/PRF/5 cells. The survival of Ead 40 and Ead 41 in primary and secondary wastewater was slightly greater than that of polio 1. However, in tap, and sea water, the enteric adenoviruses were substantially more stable than either polio 1 or HAV. These results suggest that the enteric adenoviruses may survive for prolonged periods in water, representing a potential route of transmission. © 1995.
• Gerba, C. P., Huber, M. S., Naranjo, J., Rose, J. B., & Bradford, S. (1995). Occurrence of enteric pathogens in composted domestic solid waste containing disposable diapers. Waste Management and Research, 13(4), 315-324.
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  Abstract: Information has not been previously available on the occurrence of enteric pathogenic viruses and protozoan parasites in composted municipal domestic solid waste. A potential source of these pathogens in domestic solid waste is disposal diapers. The occurrence of enteroviruses, Giardia cysts, Cryptosporidium oocysts and Salmonella were determined in municipal composted domestic solid waste, and solid waste to which extra diapers had been added to increase their concentration 2-4 fold (6.6-7.7% by weight) above that found normally in municipal solid waste before composting. The compost was tested at various periods of time during aging (101-203 days). No enteroviruses or protozoan cysts or oocysts were detected in any of the samples collected during this period. One sample out of 19 collected (after 175 days aging) was positive for Salmonella. These results suggest that enteric pathogens were destroyed during the composting process, or were present in numbers below the detection method (i.e. one organism per 40-50g of compost) used in this study. © 1995.
• Gerba, C. P., Straub, T. M., Rose, J. B., Karpiscak, M. M., Foster, K. E., & Brittain, R. G. (1995). Water quality study of graywater treatment systems. Water Resources Bulletin, 31(1), 109-116.
• Straub, T. M., Gerba, C. P., Zhou, X., Price, R., & Yahya, M. T. (1995). Synergistic inactivation of Escherichia coli and MS-2 coliphage by chloramine and cupric chloride. Water Research, 29(3), 811-818.
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  Abstract: Reaction of free chlorine with organic compounds in water during drinking water treatment may lead to the formation of potentially carcinogenic compounds known as trihalomethanes (THMs). Monochloramine and metals have been investigated as alternative disinfectants. However, the action of either disinfectant alone requires greater concentrations and longer contact times compared to free chlorine. This experiment evaluated the efficacy of combining monochloramine (1-2.5 mg/l) and copper in the form of cupric chloride (0.1-0.8 mg/l) to determine if inactivation of MS-2 coliphage and Escherichia coli was synergistic and thereby decreasing the concentration and contact time for adequate inactivation of these organisms. Combination of 5 mg/l monochloramine and 0.1-0.4 mg/l cupric chloride was sufficient to produce a 3 log10 inactivation of MS-2 coliphage after 10 min. Nearly 120 min was required for the same log10 inactivation of MS-2 using 5 mg/l monochloramine alone and less than a 0.5 log10 reduction was observed after 120 min using 0.4 mg/l cupric chloride alone. A 6 log10 reduction of E. coli was observed after 10- and 20-min exposures to 2.5 mg/l monochloramine and 0.8 or 0.4 mg/l cupric chloride, respectively. To achieve the same inactivation of E. coli using monochloramine alone, a concentration and contact time of 5 mg/l for 60 min was required. No inactivation of E. coli was observed after exposure to 0.4 or 0.8 mg/l cupric chloride after 60 min. Synergism was demonstrated in the inactivation of both organisms using the combined chloramine copper system. © 1995.
• Wilson, L. G., Amy, G. L., Gerba, C. P., Gordon, H., Johnson, B., & Miller, J. (1995). Water quality changes during soil aquifer treatment of tertiary effluent. Water Environment Research, 67(3), 371-376.
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  Abstract: This paper summarizes the results of field studies in Tucson, Arizona, to estimate the soil aquifer treatment (SAT) effectiveness of a 5.7-ha (14- acre) water spreading facility, the Sweetwater Underground Storage and Recovery Facility. Groundwater samples collected from the facility during 1989 to 1990 were analyzed for pathogens. A specific basin was selected during the 1990 to 1991, 1991 to 1992, and 1992 to 1993 recharge seasons for sampling source water (tertiary effluent), pore-liquid samples from the vadose zone, and groundwater during recharge. These samples were analyzed for the nitrogen species, dissolved organic carbon (DOC), and total organic halide (TOX). The results showed that the site provides effective SAT. Enteroviruses were completely removed during travel in the 37-m (120-ft) thick vadose zone. No Giardia were detected in any of the groundwater samples. The DOC and TOX were reduced by 92% and 85%, respectively. After leaching of indigenous nitrogen from the vadose zone, total nitrogen was reduced by approximately 47% during recharge. Near-surface anaerobic conditions promote denitrification.
• Brion, G., Gerba, C. P., & Silverstein, J. (1994). Pathogenic viruses in space: Indicators and risks in closed space environments. SAE Technical Papers.
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  Abstract: Astronauts working in space for extended periods of time will be in a closed environment where both air and water are recycled. As the lengths of missions increase, the astronauts are likely to be at greater risk for viral infection by consumption of recycled water and air. In order to minimize the risk of infection and assure mission success, indicators of the viral quality of recycled water and air will have to be determined. The indicators chosen will depend upon many factors arising from the fields of engineering, public health, virology, and infectious disease. Moreover, selection of viral indicators must address the unavoidable mixing of recycled air and water and the pathogens they contain. This paper is a discussion defining viral quality indicators for potable recycled water and air that reflect the behavior of viruses in a closed, multimedia, space environment The applicability of indicators currently used on earth are considered for use in space. Several viral indicators are proposed for use in monitoring the risks anticipated, and the idea of indicator seeding at various points in the closed environment is presented. © Copyright 1994 Society of Automotive Engineers, Inc.
• Huber, M. S., Gerba, C. P., Abbaszadegan, M., Robinson, J. A., & Bradford, S. M. (1994). Study of persistence of enteric viruses in landfilled disposable diapers. Environmental Science and Technology, 28(9), 1767-1772.
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  Abstract: Disposable diapers are one of many possible sources of infectious enteric viruses that are disposed of in landfills. A total of 218 disposable diapers were collected from 7 sites and 10 depths at three landfills. Of this total, 110 diapers were selected to be processed based on fecal content using a 1.5% beef extract elution, organic flocculation-concentration method to recover viruses. The concentrated samples were assayed on Buffalo Green Monkey (BGM) kidney cell cultures for the detection of enteroviruses and with cDNA probes specific for poliovirus, hepatitis A virus, and rotavirus. Enteroviruses were not detected in any sample assayed using cell culture techniques. Three samples were positive using nucleic acid probes for poliovirus while negative for rotavirus and hepatitis A. These results suggest that, although poliovirus RNA was present in some diapers, the viruses were not viable by cell culture assays after 2 years or longer in a landfill.
• Ma, J. -., Naranjo, J., & Gerba, C. P. (1994). Evaluation of MK filters for recovery of enteroviruses from tap water. Applied and Environmental Microbiology, 60(6), 1974-1977.
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  PMID: 8031090;PMCID: PMC201589;Abstract: The MK filter is an electropositively charged filter that can be used to concentrate enteroviruses from large volumes (400 to 1,000 liters) of water. This filter is less expensive than the commonly used 1MDS electropositive filter. In this study, we compared the recovery of poliovirus 1 (PV1) and that of coxsackievirus B3 (CB3) from 378 liters of tap water, using both the MK and the 1MDS filters. Viruses were eluted from the filters with 3% beef extract buffered with 0.05 M glycine (pH 9.5) and reconcentrated via organic flocculation. At high virus inputs (approximately 106 PFU), the overall recovery (after elution and reconcentration) of PV1 and CB3 from tap water with the MK filter was less than that achieved with the 1MDS filter (P < 0.05). The recoveries of PV1 from tap water with the MK and 1MDS filters were 73.2% ± 26% (n = 5 trials) and 90.2% ± 5.9% (n = 5 trials), respectively. The recoveries of CB3 from tap water with the MK and 1MDS filters were 32.8% ± 34.5% (n = 4 trials) and 95.8% ± 12.0% (n = 4 trials), respectively. This study indicated that the MK filter consistently provided lower recovery, with wider variability, of PV1 and CB3 from tap water than the 1MDS filter.
• Powelson, D. K., & Gerba, C. P. (1994). Virus removal from sewage effluents during saturated and unsaturated flow through soil columns. Water Research, 28(10), 2175-2181.
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  Abstract: Recharge of sewage effluents may lead to contamination of groundwater with viruses. The goal of this research was to quantify virus removal in representative subsurface transport conditions. Soil column and batch studies were conducted to evaluate how virus type, effluent type and water saturation affect virus adsorption and removal. Three viruses were used: MS2 and PRD1 bacteriophages and poliovirus type 1. In the first column study, secondary- or tertiary-treated sewage containing the viruses percolated through coarse-sand columns under unsaturated conditions. In the second column study, the viruses suspended in secondary-treated sewage percolated through the columns under saturated or unsaturated conditions. A batch adsorption study was conducted to determine equilibrium adsorption of these viruses to the sand. Effluent type had no significant effect on first-order virus removal coefficients or retardation of virus transport. Virus 'removal' was considered to be inactivation or irreversible adsorption. Unsaturated conditions resulted in an average removal coefficient (μ(s) = 0.31 h-1) more than three times greater than saturated conditions (μ(s) = 0.095 h-1), a significant difference at the 0.01 level. Poliovirus had a greater retardation coefficient (R = 5.2) than the bacteriophages (MS2, R = 1.4; and PRD1, R = 2.2), a significant difference at the 0.001 level. Column retardations of virus transport were only 0.8-8.0% of that predicted by adsorption coefficients determined from the batch studies. Equations developed in this paper may aid in estimating virus removal during recharge of effluents if the water residence times in ponds, the vadose zone and the aquifer are known.
• Abbaszadegan, M., Gerba, C. P., Yahya, M. T., & Rusin, P. (1993). Evaluation of a microbiological water purifier for inactivation of viruses, bacteria and Giardia cysts. Water Science and Technology, 27(3-4), 329-333.
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  Abstract: Development of the need for personal water treatment devices has evolved from consumer interest in improving and ensuring the quality of drinking water. The need also extends to the quality of untreated or partially treated waters such as that used by hikers, campers, recreational home and boat owners, and families or communities having individual home and small system water sources. It is essential that such devices be capable of removing all types of pathogenic microorganisms likely to be found in contaminated water. For this reason the U.S. Environmental Protection Agency has suggested such units be capable of removing Klebsiella terrigena, Giardia cysts and enteric viruses. Three identical water purifiers were evaluated for the inactivation of rotavirus SA-11, hepatitis A virus, poliovirus type 1, the bacterial virus MS-2, Klebsiella terrigena and Giardia muris cysts. The units depend upon a thermal cycler combined with activated carbon for removal of the test organisms. The units were challenged with the organisms suspended in tapwater after 4, 76 and 240 cycles of operation. The units were also tested with a 'worst case' water quality of 1500 mg/l dissolved solids, 10 mg/l organic matter and with a water turbidity of 30 NTU. In all cases, complete inactivation of the viruses, bacteria and cysts occurred after operation of the 35-minute cycle. This resulted in a greater than 3-log (99.9%) inactivation of cysts, a greater than 6 log (99.9999%) inactivation of K. terrigena and 4-log (99.99%) inactivation of viruses. In conclusion, these units would comply with criteria guidelines suggested by the U.S. Environmental Protection Agency for the operation of microbial water purifiers.
• Deflaun, M. F., & Gerba, C. P. (1993). Monitoring recombinant DNA microorganisms and viruses in soil. Soil microbial ecology, 131-150.
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  Abstract: Methods to monitor survival, transport and ecological impact of genetically engineered microorganisms (GEMs) and their recombinant genes in the soil environment are briefly described. Methods are introduced for: genetic and phenotypic marking of GEMs; measuring processes of genetic exchange in the soil; monitoring of bacterial survival in the soil; biological containment of GEMs; and detecting viruses in the soil, including bacterial and animal viruses. -J.W.Cooper
• Haas, C. N., Rose, J. B., Gerba, C., & Regli, S. (1993). Risk assessment of virus in drinking water. Risk Analysis, 13(5), 545-552.
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  PMID: 8259444;Abstract: The reevaluation of drinking water treatment practices in a desire to minimize the formation of disinfection byproducts while assuring minimum levels of public health protection against infectious organisms has caused it to become necessary to consider the problem of estimation of risks posed from exposure to low levels of microorganisms, such as virus or protozoans, found in treated drinking water. This paper outlines a methodology based on risk assessment principles to approach the problem. The methodology is validated by comparison with results obtained in a prospective epidemiological study. It is feasible to produce both point and interval estimates of infection, illness and perhaps mortality by this methodology. Areas of uncertainty which require future data are indicated.
• Kinoshita, T., Bales, R. C., Maguire, K. M., & Gerba, C. P. (1993). Effect of pH on bacteriophage transport through sandy soils. Journal of Contaminant Hydrology, 14(1), 55-70.
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  Abstract: Concentrations of the lipid-containing phage PRD-1 decreased 3-4 orders of magnitude during passage through the 10-15-cm-long columns. Attachment of the lipid-containing phage, PRD-1 was insensitive to pH and was apparently controlled by hydrophobic interactions in soil media. The less-hydrophobic phage MS-2 acted conservatively; it was not removed in the columns at pH's 5.7-8.0. The sticking efficiency (α) in a colloid-filtration model was between 0.1 and 1.0 for PRD-1, indicating a relatively high removal efficiency. Phage attachment was reversible, but detachment under steady-state conditions was slow. An increase in pH had a moderate effect on enhancing detachment. Still, these soils should continue to release phage to virus-free water for days to weeks following exposure to virus-containing water. -from Authors
• Kinoshita, T., Bales, R. C., Yahya, M. T., & Gerba, C. P. (1993). Bacteria transport in a porous medium: Retention of bacillus and pseudomonas on silica surfaces. Water Research, 27(8), 1295-1301.
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  Abstract: Pseudomonas fluorescens and Bacillus subtilis transport was studied in water flowing through laboratory columns packed with 0.5-mm silica beads. The rate of bacterial attachment to the silica was shown to reach steady state after about one pore volume of bacteria-containing solution had passed through the column. Column-outlet concentrations were 6-80% of inlet concentrations. There was less P. fluorescens retardation at pH 5.5 versus 7.0; since the pH(iep)s (isoelectric point) for both bacteria are at lower pHs, this difference indicates that the change in electrostatic repulsion over this pH range was relatively unimportant in determining bacteria retention in the porous medium. Transport of both species was highly retarded, suggesting that neither could be quickly transported over long distances in sandy soils. Results were adequately described using a steady-state transport model with bacterial attachment to soil as a pseudo-first-order process. Sticking efficiency (α), calculated using the steady-state colloid-filtration model, was near one. The continued appearance of bacteria in the column effluent for several pore volumes after switching to a bacteria-free inlet solution shows attachment to be reversible, though slowly reversible.
• Leon, R. D., Rose, J. B., Bosch, A., Torrella, F., & Gerba, C. P. (1993). Detection of Giardia, Cryptosporidium and enteric viruses in surface and tap water samples in Spain. International Journal of Environmental Health Research, 3(3), 121-129.
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  Abstract: Numerous outbreaks of waterborne gastrointestinal disease have been attributed to Giardia, Cryptosporidium, and rotaviruses. The presence of these organisms in surface water and in treated tap water poses a public health risk. We conducted a pilot survey of surface and tap water in Spain to determine the level of Giardia, Cryptosporidium, enterovirus and rotavirus contamination. Five out of eight surface water samples tested (63%) were positive for Giardia, four out of eight (50%) were positive for Cryptosporidium, and two out of seven (29%) were positive for enteric viruses. Seven out of ten surface waters tested (70%) were positive for an enteric pathogen. Two out of nine (22%), three out of nine (33%) and two out of 11 (18%) tap water samples tested were positive for Giardia, Cryptosporidium, and enteric viruses, respectively. Five out of 13 samples tested (45%) were positive for an enteric pathogen. These results suggest that the extent of source water contamination, the pathogen removal efficiency of drinking water treatment plants, and the associated risks to the population need to be further investigated.
• Margolin, A. B., Gerba, C. P., Richardson, K. J., & Naranjo, J. E. (1993). Comparison of cell culture and a poliovirus gene probe assay for the detection of enteroviruses in environmental water samples. Water Science and Technology, 27(3-4), 311-314.
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  Abstract: Nucleic acid hybridization provides a rapid non-cell culture method for the detection of enteric viruses in water. The purpose of this work was to compare the detection of naturally occurring enteroviruses by cell culture with their detection by a poliovirus gene probe in various types of water samples. Samples of activated sludge effluent, tertiary treated wastewater (activated sludge, filtration and passage through reverse osmosis), ground water, surface water and tidal river water were processed through 1 MDS Virozorb filters to concentrate any naturally occurring virus. Viruses were eluted from the filters with pH 9.5 beef extract and reduced in volume by flocculation to 20-30 ml. These concentrates were then assayed in the BGM cell line by the cytopathogenic effects (CPE) method and by a poliovirus cDNA probe (base pairs 115-7440) labeled with 32P, A total of 233 samples were assayed in this manner. In slightly more than 93% of the samples gene probe and cell culture yielded the same results. Of these samples 36 were positive by gene probe and 28 by cell culture assay. Positive samples for gene probe were confirmed by treatment with NaOH or RNAse and then reprobed. Samples demonstrating CPE upon primary passage were confirmed positive by subsequent passage of cell lysate on a new monolayer of BGM cells. Ten samples were positive by gene probe and negative by cell culture, and 4 samples were negative by gene probe and positive by cell culture.
• McKay, L. D., Cherry, J. A., Bales, R. C., Yahya, M. T., & Gerba, C. P. (1993). A field example of bacteriophage as tracers of fracture flow. Environmental Science and Technology, 27(6), 1075-1079.
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  Abstract: Two bacteriophages, MS-2 and PRD-1, were added to water to an initial concentration of 105-106 pfu mL-1 in a trench-to-trench lateral groundwater flow and tracer migration experiment in the upper 5.5 m of a weathered and fractured clay-rich till. Phage were detected in water from seepage collectors set in the wall of a downgradient (gradient = 0.24) trench, located 4 m from the source trench, between 1 and 2 days after the start of the injection. Peak phage concentrations in the collectors were typically 102-104 pfu mL-1, and detectable phage (>0.1 pfu mL-1) persisted for up to 5 days. In contrast, the travel time for bromide in the same trenches was several months. The colloidal phage are believed to have moved mainly through fractures with little diffusion into pores of the clay matrix. Phage attenuation was due to inactivation and either attachment to the fracture walls or diffusion into the larger pores. At the temperature of the current experiment (10-12 °C), phage inactivation rates were sufficiently low to permit their use as groundwater tracers over periods of several days. © 1993 American Chemical Society.
• Naranjo, J. E., Gerba, C. P., Bradford, S. M., & Irwin, J. (1993). Virus removal by an on-site wastewater treatment and recycling system. Water Science and Technology, 27(3-4), 441-444.
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  Abstract: On-site wastewater reclamation and recycling systems are a useful option in areas where moratoriums exist on sewer connections or water shortages encourage maximum use of all water resources. The Cycle-Let Recycling System is used to treat wastewater from offices, shopping centers, and commercial and public facilities. The system is designed to produce reclaimed water for toilet and urinal flushing or landscape irrigation by anoxic and aerobic biological treatment followed by ultrafiltration, passage through activated carbon, and disinfection by ultraviolet light. A full scale operating system was evaluated for its removal of the coliphage MS-2, rotavirus SA-11, poliovirus type 1 by seeding these viruses into the mixed liquor tanks before treatment. In addition, samples were collected for naturally occurring viruses after completion of the tests. Four hundred liter samples were processed and tested for the animal viruses after each of the treatment processes. No animal viruses could be detected after ultrafiltration,indicating a reduction of at least 99.9998%. MS-2 coliphage was reduced by 99.93% by the ultrafilter and more than 99.999% after disinfection. It appears that detectable levels of animal viruses are unlikely to survive this treatment process.
• Powelson, D. K., Gerba, C. P., & Yahya, M. T. (1993). Corrigendum: Virus transport and removal in wastewater during aquifer recharge (Water Research(1993)27(583-590)). Water Research, 27(8), 1401-.
• Powelson, D. K., Gerba, C. P., & Yahya, M. T. (1993). Virus transport and removal in wastewater during aquifer recharge. Water Research, 27(4), 583-590.
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  Abstract: To assess soil-aquifer treatment of sewage effluent for removal of viruses, studies were conducted at a recharge/recovery site near Tucson, Ariz. Two 13 m2 basins were constructed in coarse sand alluvium, one for secondary- and one for tertiary-treated effluent. Bacterial viruses, MS2 and PRD1, and a chemical tracer, potassium bromide (KBr), were added to effluent applied to these basins. Infiltration rates ranged from 0.2 to 16.8 m/d. Samples of unsaturated flow from depths of 0.30-6.08 m below the basin were taken through porous stainless steel suction-samplers. Bromide and virus results indicated the presence of preferential flow conditions that produced irregular concentration profiles with depth. Virus transport was retarded (R = 1.9) at the beginning of a flooding cycle, but viruses were transported faster than the average water velocity (R = 0.47) when applied after the infiltration rate had declined following 4 days of flooding. Virus specific removal rates (b) during percolation through soil were 2.3-120 times greater than in bottles of effluent or ground water. PRD1 was removed more rapidly during percolation (b = 0.65 h-1) than MS2 (b = 0.23 h-1). Effluent type did not significantly affect b for MS2, but the PRD1 rate was nearly 3 times greater with secondary effluent (1.0 h-1) compared to tertiary effluent (0.35 h-1). Virus removals at the 4.3 m depth ranged from 37 to 99.7%.
• Sobsey, M. D., Dufour, A. P., Gerba, C. P., LeChevallier, M. W., & Payment, P. (1993). Using a conceptual framework for assessing risks to health from microbes in drinking water. Journal / American Water Works Association, 85(3), 44-48.
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  Abstract: The US goal to reduce health risks from environmental exposures of all kinds has resulted in the need to assess the risks from exposure to microbes in drinking water. One way of doing this is to define and use a risk-based conceptual framework and strategy, which involves systematically identifying, analyzing, quantifying, and characterizing these microbial risks; comparing them with the risks from chemicals, especially disinfectants and their by-products; and then defining and implementing a risk management plan that presents the lowest risk to the consumer.
• Yahya, M. T., Cluff, C. B., & Gerba, C. P. (1993). Virus removal by slow sand filtration and nanofiltration. Water Science and Technology, 27(3-4), 445-448.
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  Abstract: Water utilities, especially smaller ones, are having increasing difficulties proving increased treatment requirements required in the United States for the removal of chemical and microbial contaminates in drinking water. This project sought to evaluate the virus removal potential of combined slow sand filtration and nanofiltration by a pilot plant for application to a small utility which uses a surface water supply. Nanofiltration is a relatively new water treatment technology which has become available since 1986. It is similar to reverse osmosis but has a higher molecular weight cut-off and is less costly to operate. The bacteriophages MS-2 (28 nm) and PRD-1 (65 nm) were seeded into surface water entering a pilot plant and samples collected after sand filtration, nanofiltration, and of the nanofilter reject water. These phages were selected for study because of their small size and poor adsorption to surfaces. The slow sand filter removed 99% of the MS-2 and 99.9% of the PRD-1. There was between a 4 to 6 log reduction of the phages by the nanofilters. PRD-1 was removed to a greater extent than MS-2 by both the sand filter and the nanofilters.
• Yahya, M. T., Galsomies, L., Gerba, C. P., & Bales, R. C. (1993). Survival of bacteriophages MS-2 and PRD-1 in ground water. Water Science and Technology, 27(3-4), 409-412.
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  Abstract: Bacteriophages are potentially useful models for studying the fate and transport of pathogenic enteric viruses and other biocolloids through soil and ground water. To be useful for this purpose they must be capable of surviving for significant periods in ground water and demonstrate low adsorption to soil surfaces. The purpose of this study was to evaluate the survival of two bacteriophages which have been shown to adsorb poorly to soils, i.e. the Escherichia coli phages MS-2 and PRD-1 which infect Salmonella typhimurium. Samples of ground water from various regions of North America were inoculated with the test phages and incubated at temperatures near the ambient ground water temperature of the collection site. At 7° C no significant inactivation of the phages occurred over a period of 80 days. At higher temperature (10 to 23° C) PRD-1 was far more resistant to inactivation than MS-2, persisting for periods of 7° to 10 times longer in most water samples.
• Rusin, P. A., Sinclair, N. A., Gerba, C. P., & Gershman, M. (1992). Application of phage typing to the identification of sources of groundwater contamination. Journal of Contaminant Hydrology, 11(1-2), 173-188.
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  Abstract: Phage typing of Escherichia coli populations was used as a "fingerprinting' tool to identify the source(s) of fecal coliform contamination of a drinking water well, PW-12. Group discriminate analysis was used to evaluate the data and determine the relative distance of population centroids from the centroid of the PW-12 population. The phage typing patterns were compared to serological results and correlations noted. Phage typing patterns were shown to be stable following 32-days incubation of E. coli isolates in garden soil, tap water and neutralized tertiary effluent, with and without the presence of autochthonous flora. -Authors
• Suflita, J. M., Gerba, C. P., Ham, R. K., Palmisano, A. C., Rathje, W. L., & Robinson, J. A. (1992). The world's largest landfill: a multidisciplinary investigation. Environmental Science & Technology, 26(8), 1486-1494.
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  Abstract: Samples were taken from sites within the Fresh Kills landfill, New York and dated by means of newspaper remains. The rubbish was sorted and analysed for cellulose, lignin and volatile solids contents and the cellulose:lignin ratio used as a measure of decomposition. Enzyme assays for decomposer enzymes were also made and diapers were collected for virus and bacterial assays. Moisture was important in determining degree of decomposition, which was much slower than anticipated. Methane generation depended directly on moisture content. Pathogenic organisms did not survive for very long. -B.Moss
• Yahya, M. T., Cassells, J. M., Straub, T. M., & Gerba, C. P. (1992). Reduction of microbial aerosols by automatic toilet bowl cleaners. Journal of Environmental Health, 55(3), 32-34.
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  Abstract: Microbial contamination of bathrooms by aerosols generated by toilet flushing has been previously demonstrated. In this study, the impact of automatic bowl cleaners on aerosol generation was evaluated. Three toilet bowl cleaners which contained 2.5, 6.7 or 18.2% surfactant materials were evaluated. Results indicated that these cleaners significantly (p≤0.05) reduced the numbers of bacteria ejected from the bowl, and that the cleaner containing the greatest amount of surfactant was the most effective in aerosol reduction.
• Yahya, M. T., Straub, T. M., & Gerba, C. P. (1992). Inactivation of coliphage MS-2 and poliovirus by copper, silver, and chlorine. Canadian Journal of Microbiology, 38(5), 430-435.
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  PMID: 1322762;Abstract: The efficacy of electrolytically generated copper and silver ions (400 and 40 μg/L, respectively) was evaluated separately and in combination with free chlorine (0.2 and 0.3 mg/L) for the inactivation of coliphage MS-2 and poliovirus type 1 in water at pH 7.3. The inactivation rate was calculated as log10 reduction/min: k = -(log10 C(t)/C0)/t. The inactivation of both viruses was at least 100 times slower in water containing 400 and 40 μg/L copper and silver, respectively (k = 0.023 and 0.0006 for MS-2 and poliovirus, respectively), compared with water containing 0.3 mg/L free chlorine (k = 4.88 and 0.036). Significant increases in the activation rates of both viruses were observed in test systems containing 400 and 40 μg/L copper and silver, respectively, with 0.3 mg/L free chlorine when compared with the water systems containing either metals or free chlorine alone. Poliovirus was approximately 10 times more resistant to the disinfectants than coliphage MS-2. This observation suggests either a synergistic or an additive effect between the metals and chlorine for inactivation of enteric viruses. Use of copper and silver ions in water systems currently used in swimming pools and spas may provide an alternative to high levels of chlorination.
• Abbaszadegan, M., Gerba, C. P., & Rose, J. B. (1991). Detection of Giardia cysts with a cDNA probe and applications to water samples. Applied and Environmental Microbiology, 57(4), 927-931.
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  PMID: 2059051;PMCID: PMC182824;Abstract: Giardiasis is the most common human parasite infection in the United States, causing a lengthy course of diarrhea. Transmission of Giardia species is by the fecal-oral route, and numerous waterborne outbreaks have been documented. The Environmental Protection Agency has regulated Giardia species in drinking water through the Surface Water Treatment Rule. Current methods for detection of Giardia species in water rely primarily on microscopic observation of water concentrates with immunofluorescence techniques. We evaluated the efficacy of using a gene-specific probe for the detection of Giardia species in water. A cDNA probe, 265 bp long, from the small subunit of rRNA of Giardia lamblia was used for detection of cysts. The replicative form of the M13 vector with an insert was isolated from lysed host Escherichia coli XL1-Blue and used for production of the cDNA probe by nick translation with 32P-labeled nucleotides. Six different protocols were tested for extracting nucleic acids from the cysts. With the most efficient procedure, disrupting Giardia cysts with glass beads in the presence of proteinase K, as few as 1 to 5 cysts per ml can be detected in water sample concentrates with dot blot hybridization assays.
• Bales, R. C., Hinkle, S. R., Kroeger, T. W., Stocking, K., & Gerba, C. P. (1991). Bacteriophage adsorption during transport through porous media: Chemical perturbations and reversibility. Environmental Science and Technology, 25(12), 2088-2095.
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  Abstract: In a series of seven column experiments, attachment of the bacteriophage PRD-1 and MS-2 to silica beads at pH's 5.0-5.5 was at least partially reversible; however, release of attached phage was slow and breakthrough curves exhibited significant tailing. Rate coefficients for attachment and detachment were on the order of 10-4 and 10-6-10-4 s-1, respectively. Corresponding time scales were hours for attachment and days for detachment. The sticking efficiency (α) for phage attachment was near 0.01. The rate of phage release was enhanced by raising pH and introducing surface-active chemical species, illustrating the importance of chemical perturbations in promoting biocolloid transport. In a series of batch experiments, MS-2 adsorbed strongly to a hydrophobic surface, octadecyl-trichlorosilane-bonded silica, at both pH's 5 and 7. Adsorption to the unbonded silica at pH 5 was linear, but was 2.5 (with Ca2+) to 0.25% (without Ca2+) of that to the bonded surface. Neither MS-2 nor PRD-1 adsorbed to unbonded silica at pH 7. Hydrophobic effects appear to be important for adsorption of even relatively hydrophilic biocolloids.
• Gerba, C. P., Powelson, D. K., Yahya, M. T., Wilson, L. G., & Amy, G. L. (1991). Fate of viruses in treated sewage effluent during soil aquifer treatment designed for wastewater reclamation and reuse. Water Science and Technology, 24(9), 95-102.
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  Abstract: Land application or soil aquifer treatment of wastewater has been considered as a low-cost method for improving its quality for potential reuse. The objective of this work was to evaluate more quantitatively than in the past the fate and removal of viruses as they pass through the soil. A mini-basin (12 feet x 12 feet) was constructed at a site where secondary treated wastewater will be applied to large basins for underground storage. Suction samplers were placed at various depths in the upper 20 feet of the vadose zone directly beneath the mini-basin, and monitoring wells were placed at various distances (10 to 150 feet) from the mini-basin. Two experiments (August and September, 1990) were conducted where bacteriophage MS-2 and PRD-1 were added to the effluent before its application to the basins. High infiltration rate (up to 50 feet/day) and impeding layers at 15ft resulted in nearly saturated flow conditions and up to 150ft of horizontal transport of the viruses. The results also indicated that at least 90% removal of MS-2 and 99% removal of PRD-1 could be expected after movement of the sewage through 15ft of soil and greater removal was observed at a slower infiltration rate (3 feet/day).
• Hurst, C. J., Schaub, S. A., Sobsey, M. D., Farrah, S. R., Gerba, C. P., Rose, J. B., Goyal, S. M., Larkin, E. P., Sullivan, R., Tierney, J. T., O'Brien, R., Safferman, R. S., Morris, M. E., Wellings, F. M., Lewis, A. L., Berg, G., Britton, P. W., & Winter, J. A. (1991). Multilaboratory evaluation of methods for detecting enteric viruses in soils. Applied and Environmental Microbiology, 57(2), 395-401.
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  PMID: 1849712;PMCID: PMC182723;Abstract: Two candidate methods for the recovery and detection of viruses in soil were subjected to round robin comparative testing by members of the American Society for Testing and Materials D19:24:04:04 Subcommittee Task Group. Selection of the methods, designated 'Berg' and 'Goyal', was based on results of an initial screening which indicated that both met basic criteria considered essential by the task group. Both methods utilized beef extract solutions to achieve desorption and recovery of viruses from representative soils: a fine sand soil, an organic muck soil, a sandy loam soil, and a clay loam soil. One of the two methods, Goyal, also used a secondary concentration of resulting sand eluents via low-pH organic flocculation to achieve a smaller final assay volume. Evaluation of the two methods was simultaneously performed in replicate by nine different laboratories. Each of the produced samples was divided into portions, and these were respectively subjected to quantitative viral plaque assay by both the individual, termed independent, laboratory which had done the soil processing and a single common reference laboratory, using a single cell line and passage level. The Berg method seemed to produce slightly higher virus recovery values; however, the differences in virus assay titers for samples produced by the two methods were not statistically significant (P ≤ 0.05) for any one of the four soils. Despite this lack of a method effect, there was a statistically significant laboratory effect exhibited by assay titers from the independent versus reference laboratories for two of the soils, sandy loam and clay loam.
• Karpiscak, M. M., Brittain, R. G., Gerba, C. P., & Foster, K. E. (1991). Demonstrating residential water conservation and reuse in the Sonoran desert: Casa del Agua and Desert House. Water Science and Technology, 24(9), 323-330.
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  Abstract: Single-family homes are being used to demonstrate and research water conserving and reuse techniques and technologies. These facilities can provide real-world data as well as public information and educational programs. The installation of water-conserving fixtures, rainwater harvesting, and graywater reuse systems and storage can reduce the requirements for potable water by 50 percent. Casa del Agua and Desert House show that the science of conserving resources can be balanced with the art of designing quality desert dwellings.
• Leon, R. D., & Gerba, C. P. (1991). Detection of rotaviruses in water by gene probes. Water Science and Technology, 24(2), 281-284.
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  Abstract: Gene probes and other molecular techniques are a novel approach for the detection of enteric viruses in water. Gene probe hybridization to genomic viral RNA has been reported to detect 2.5 × 105 physical particles of SA-11 rotavirus (Dimitrov et al., 1985), 104 physical particles of hepatitis A virus (Jiang et al., 1986), 500-1000 PFU of SA-11 (De Leon, 1989), and 500-1000 PFU of coxsackie B3 (Shieh et al., 1990, submitted). When determinations of gene probre sensitivity are made in environmental concentrates a 100-fold decrease in signal may be observed (De Leon, 1989). Probe sensitivity in environmental samples can be enhanced with other molecular techniques. Sephadex G-200 spun columns (De Leon, 1989) or Centricon ultrafiltration membranes (Sobsey, 1990) can remove proteins and other interfering factors from water concentrates. The passage of environmental concentrates through Sephadex G-200 spun columns can result in a 10 to 1000-fold increase in detection of viruses (De Leon, 1989). Target nucleic acid amplification is the most feasible alternative for achieving the sensitivity limits needed for environmental samples. Cell culture (Shieh et al., 1990), rotavirus incorporated transcriptase (De Leon, 1989) and Polymerase Chain Reaction (Shieh et al., 1990; Sobsey and De Leon, 1990) have been used to amplify viral sequences in environmental samples. In this study, the rotavirus incorporated transcriptase was used to amplify rotaviral mRNA in environmental samples prior to detection by gene probes.
• Margolin, A. B., Hewlett, M. J., & Gerba, C. P. (1991). The application of a poliovirus cDNA probe for the detection of enteroviruses in water. Water Science and Technology, 24(2), 277-280.
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  Abstract: A technique for the detection of enteroviruses in water using gene probes in a dot blot assay is described. Poliovirus cDNA probes were labeled with [32P] dCTP and [32P] dATP to a specific activity greater than 2.0 x 109 cmp/μg DNA. Autoradiograph times were compared to determine the minimum time required to optimize the sensitivity of the test. One infectious unit of poliovirus was detected from cell harvests within 38 hours using gene probes. Potential false positive reactions between bacterial DNA in environmental samples and vector DNA were controlled by both base hydrolysis of viral RNA and enzymatic treatment of the sample. Upon comparison to cell culture, the dot blot assay was as sensitive for the detection of virus in sewage contaminated groundwater.
• Powelson, D. K., Simpson, J. R., & Gerba, C. P. (1991). Effects of organic matter on virus transport in unsaturated flow. Applied and Environmental Microbiology, 57(8), 2192-2196.
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  PMID: 1768089;PMCID: PMC183549;Abstract: The effects of natural humic material and sewage sludge organic matter (SSOM) derived from primary treated sewage sludge on virus transport by unsaturated flow through soil columns were evaluated. Bacteriophage MS-2 was applied to loamy fine sand columns 0.052 m in diameter and 1.05 m long. Virus concentrations in the influent and effluent were measured daily for 7 to 9 days. In the first experiment, virus transport through two fresh soil columns was compared with that through a column previously leached with more than four pore volumes (T) of well water. The soil water organic matter concentrations in the leachate of the fresh soil declined with time. Relative virus concentrations (C/C(o)) from one fresh soil column reached 0.82 in 0.9 T and then declined to 0.51 by 2.1 T. The other fresh soil column reached and maintained a steady-state relative virus concentration [(C/C(o))(s)] of 0.47 from 1.5 to 2.5 T. The leached column reached and maintained a (C/C(o))(s) of 0.05. Concentrations measured at 0.2-, 0.4-, 0.8-, and 1.05-m depths indicated that most virus particles were removed in the surface 0.2 m. In the second experiment, one leached column was pretreated with SSOM derived from primary treated sewage sludge and the other leached column was untreated. SSOM concentrations declined with depth. A suspension of virus and SSOM in well water was applied to both columns. Although the (C/C(o))(s) values were similar (0.41 for the pretreated column and 0.47 for the untreated column), breakthrough was delayed for the untreated column. Both natural humic material and sewage sludge-derived SSOM increased the unsaturated-flow transport of MS-2.
• Regli, S., Rose, J. B., Haas, C. N., & Gerba, C. P. (1991). Modeling the risk from Giardia and viruses in drinking water. Journal / American Water Works Association, 83(11), 76-84.
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  Abstract: This article discusses the assessment of risk from microorganisms in drinking water, the problems associated with such an analysis, the approach for specific organisms, the monitoring required to demonstrate that risk levels are met, and how risk assessment might be approached for determining whether a given level of risk from Giardia and viruses is avoided. Guidelines are suggested for determining the level of treatment necessary to ensure that consumers receive a finished drinking water with risks of less than one infection per 10,000 people per year from Giardia and enteric viruses.
• Rose, J. B., & Gerba, C. P. (1991). Assessing potential health risks from viruses and parasites in reclaimed water in Arizona and Florida, USA. Water Science and Technology, 23(10-12), 2091-2098.
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  Abstract: Wastewater reuse has been mandated in both the states of Arizona and Florida, U.S.A. In Arizona, standards have been set for enteric virus and Giardia levels to maintain a specified effluent quality depending on the reuse, while in Florida, specified treatment control has been implemented. Data on virus levels in treated wastewaters have been generated in both states. Average virus levels ranged from 13-130 pfu/100L after secondary treatment while with the addition of filtration, levels were reduced to averages between 0.13 to 1.25 pfu/100L. Giardia cyst levels also dropped by 100 fold after filtration averaging 0.32/40L. Using a probability of infection model, risk of infection from 100 ml accidental ingestion ranged from approximately 2 x 10-3 to 2 x 10-4 for the levels of viruses and protozoa found in chlorinated secondary effluent and the risk was reduced to 2 x 10-4 to 2 x 10-6 with filtration and disinfection following activated sludge.
• Rose, J. B., & Gerba, C. P. (1991). Use of risk assessment for development of microbial standards. Water Science and Technology, 24(2), 29-34.
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  Abstract: A single-hit exponential model and a β-distributed 'infectivity probability' model were used to evaluate the potential health risks from drinking water containing low levels of protozoan cysts and viruses, respectively. The models were based on dose response curves developed from human feeding studies and assumed consumption of 2 L/day. The US EPA has suggested that one infection/10,000/year is an acceptable risk for infectious agents acquired through potable water. Based on this risk, acceptable levels of viruses and cysts were determined using the probability models. Thus poliovirus and rotavirus levels should not be more than 0.1 and 0.3 pfu/100 L respectively per day. Giardia levels should be below 0.2 cysts/100 L. To achieve a 1:10,000 annual risk, the geometric average should not exceed 10-3 organisms/100 L. As monitoring treated water for these levels would be difficult, source waters may be monitored. Geometric averages of 1-100 organisms/100 L require 3-5 logs of treatment reduction to achieve the 1:10,000 risk. The risk models for viruses and protozoa can be used to evaluate the occurrence of pathogens in source water and determine the appropriate treatment needed to obtain specific levels of safety for drinking water.
• Rose, J. B., Gerba, C. P., & Jakubowski, W. (1991). Survey of potable water supplies for Cryptosporidium and Giardia. Environmental Science & Technology, 25(8), 1393-1400.
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  Abstract: Occurrence of the enteric protozoa Cryptosporidium and Giardia was evaluated in 257 water samples from 17 states in the USA. Cryptosporidium oocysts were detected in 55% of surface water samples at an average concentration of 43 oocysts/100 L, while Giardia cysts were found in 16% of samples at 3 cysts/100 L. Giardia and Cryptosporidium were most frequently detected in samples from waters receiving sewage and agricultural discharges. Cryptosporidium oocysts were detected in 17% of 36 drinking water samples (0.5-1.7 oocysts/100 L) while no Giardia cysts were detected. -from Authors
• Rose, J. B., Shun, G. -., Gerba, C. P., & Sinclair, N. A. (1991). Microbial quality and persistence of enteric pathogens in graywater from various househod sources. Water Research, 25(1), 37-42.
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  Abstract: This study was designed to evaluate the microbial quality and safety of graywater for reuse purposes. The microbial and chemical composition of graywater from shower/bath, wash cycle and rinse cycle of a clothes washing machine was determined. Graywater composed from all sources within a house was also monitored each week over 2-3-month time period. Samples were taken from a diverse group of families with children (18 months-9 years of age) and without children. Standard plate count bacteria (SPC) ranged from 105 to 1010 colony forming units (cfu) per 100 ml for shower and bath water, and an average of 104 to 106 cfu per 100 ml for total coliforms. Families with small children produced wash cycle graywater containing 106 cfu per 100 ml of fecal coliforms. During investigations on storage of graywater, it was found that total bacterial SPC and coliform bacteria increased one order of magnitude. Salmonella atyphimurium and Shigella dysenteriae seeded into graywater were found to persist for at least several days. Poliovirus type 1 added to graywater decreased 99 and 90% at 25 and 17°C, respectively, after 6 d of storage in graywater. These data imply that there may be some risk associated with reuse of graywater when these pathogenic bacteria or viruses are being excreted by an individual producing the graywater.
• Badawy, A. S., Rose, J. B., & Gerba, C. P. (1990). Comparative survival of enteric viruses and coliphage on sewage irrigated grass. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, 25(8), 937-952.
• Bloch, A. B., Stramer, S. L., Smith, J. D., Margolis, H. S., Fields, H. A., McKinley, T. W., Gerba, C. P., Maynard, J. E., & Sikes, R. K. (1990). Recovery of hepatitis A virus from a water supply responsible for a common source outbreak of hepatitis A. American Journal of Public Health, 80(4), 428-430.
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  PMID: 2156462;PMCID: PMC1404566;Abstract: An outbreak of hepatitis A occurred in a north Georgia trailer park served by a private well. Of 18 residents who were serosusceptible to hepatitis A virus (HAV), 16 (89%) developed hepatitis A. Well water samples were collected 3 months after illness onset in the index case and 28 days after illness onset in the last trailer park resident. Hepatitis A virus antigen (HAVAg) was detected in the samples by enzyme immunoassay from three of the five cell lines following two 30-day passages and from a fourth cell line following a third passage of 21 days.
• Bull, R. J., Gerba, C., & Trussell, R. R. (1990). Evaluation of the health risks association with disinfection. Critical Reviews in Environmental Control, 20(2), 77-113.
• Powelson, D. K., Simpson, J. R., & Gerba, C. P. (1990). Virus transport and survival in saturated and unsaturated flow through soil columns. Journal of Environmental Quality, 19(3), 396-401.
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  Abstract: Water with entrained disease-causing virus entering soil normally passes through water-saturated and unsaturated regions before reaching the groundwater. The effects of saturated and unsaturated flow on the survival and transport of a virus, MS-2 bacteriophage, were compared. The viruses were added to well water and applied to soil columns 0.052 m in diameter and 1.05 m long. The soil material was Vint loamy fine sand (a sandy, mixed, hyperthermic Typic Torrifluvent) mixed with recent alluvium. Samples of the soil water were taken daily at 0.20, 0.40, and 0.80 m depths through porous stainless steel samplers and at 1.05 m from the percolate leaving the column. For saturated flow the virus concentrations reached the influent concentration in less than two pore volumes (PV). For unsaturated flow the concentrations remained at levels much lower than the influent, ranging from 27% of inflow at 0.20 m (18 PV) to 5% at 1.05 m (3.3 PV). At the end of the experiments soil samples from each depth were assayed to determine virus adsorption to the soil. The average distribution coefficient of the unsaturated columns, 0.27, indicates very little adsorption. The number balance showed that only 39% of the unsaturated flow virus were accounted for. It appears that under unsaturated flow conditions enhanced inactivation of this virus occurs.
• Yahya, M. T., Landeen, L. K., & Gerba, C. P. (1990). Inactivation of Legionella pneumophila by potassium permanganate. Environmental Technology, 11(7), 657-662.
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  Abstract: Potassium permanganate (KMnO4) was investigated for its ability to inactivate cultures of agar-grown Legionella pneumophila in a phosphate buffer (pH 6.0 and pH 8.0) at 7°C. At pH 6.0, significantly higher inactivation rates, k values, (0.300 log10 reduction min-1) of L. pneumophila were observed compared to those at pH 8.0 (0.032 log10 reduction min-1). By exposure to 5.0 mg L-1 KMnO4, more than 99% (2 log10 cfu mL-1) reduction in the bacterial numbers was achieved within 10 minutes at pH 6.0; however, at pH 8.0, at least 60 min was required for 99% reduction. KMnO4 was significantly more effective at 5.0 mg L-1 compared to 2.5 and 1.0 mg L-1. Water systems with KMnO4 may gain disinfection credits as proposed by the U.S. Environmental Protection Agency.
• Yahya, M. T., Landeen, L. K., Messina, M. C., Kutz, S. M., Schulze, R., & Gerba, C. P. (1990). Disinfection of bacteria in water systems by using electrolytically generated copper:Silver and reduced levels of free chlorine. Canadian Journal of Microbiology, 36(2), 109-116.
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  PMID: 2337833;Abstract: As an alternative disinfectant to chlorination, electrolytically generated copper:silver (400 and 40 μg/L copper and silver, respectively) with and without free chlorine (0.3 mg/L) was evaluated over a period of 4 weeks in indoor and outdoor water systems (100 L tap water with natural body flora and urine). Numbers of total coliform, pseudomonas, and staphylococci were all less than drinking water standards in systems treated with copper:silver and free chlorine and systems treated with free chlorine alone (1.0 mg/L). No significant differences (p ≤ 0.05) in bacterial numbers were observed between systems with copper:silver and free chlorine and those with free chlorine alone. Overall, free-chlorine treatments (0.3 or 1.0 mg/L) showed significantly lower heterotrophic plate numbers than those without free chlorine. When challenged with a natural Staphylococcus sp. isolate, water with copper:silver and free chlorine had a 2.4 log10 reduction in bacterial numbers within 2 min, while free chlorine alone or copper:silver alone showed 1.5 and 0.03 log10 reductions, respectively. Addition of copper:silver to water systems may allow the concentration of free chlorine to be reduced while still providing comparable sanitary quality of the water.
• Yates, M. V., Stetzenbach, L. D., Gerba, C. P., & Sinclair, N. A. (1990). The effect of indigenous bacteria on virus survival in ground water. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, 25(1), 81-100.
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  Abstract: Over one-half of the waterborne disease outbreaks in the United States are due to the consumption of contaminated ground water. Although viruses are a major cause of illness in these outbreaks, very little is known about the factors which influence how long viruses can remain infective in ground water. Experiments were conducted using several ground water samples obtained from drinking water wells to determine the effects of the naturally-occurring bacteria on the survival of coliphage MS-2 and poliovirus type 1 inoculated into the samples. The numbers of bacteria and viruses were monitored over a 30-day period. Parallel experiments were conducted using water which had been filtered to remove the bacteria. The increase in bacterial numbers in the first 24 hours of incubation was significantly correlated with the decay rate of coliphage MS-2. However, consistent trends were found in the ability of the viruses to persist in the presence or absence of bacteria.
• Fradkin, L., Gerba, C. P., Goyal, S. M., Scarpino, P., Bruins, R. J., & Stara, J. F. (1989). Municipal wastewater sludge: The potential public health impacts of common pathogens. Journal of Environmental Health, 51(3), 148-159.
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  Abstract: Municipal wastewater sludges are known to contain microorganisms capable of causing serious illness and mortality in man. Many of these organisms are responsible for waterborne diseases in the United States today. The number of documented cases of waterborne disease has been on the increase for almost two decades. Thus, it is essential that methodologies be developed to assess risks from microorganisms during sludge disposal so that appropriate criteria can be developed for their management.
• Gerba, C. P., Margolin, A. B., & Hewlett, M. J. (1989). Application of gene probes to virus detection in water. Water Science and Technology, 21(3), 147-154.
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  Abstract: Gene probes offer a rapid and sensitive method for the detection of viruses in water and other environmental samples. Gene probes are small strands of nucleic acid labeled with radioactive or nonradioactive compounds for their detection. The target organism is identified by the hybridization of the probe oto the organism's nucleic acid. Nucleic acid probes are at least 1000-fold more sensitive than serological tests such as enzyme-linked-immunoassay and do not first require cultivation of the virus for detection. Gene probes have been developed for organisms that do not grow in cell culture, and probes have been constructed for most of the major groups of enteric viruses. Gene probes have been applied to the detection of enteric viruses in water, marine sediment and shellfish. Radioactively labeled probes can detect as little as 1-10 infectious units of virus within 48 hours. A current disadvantage of probes is that they cannot determine the infectivity of the viruses; however, they can be used to quickly determine the growth of viruses in cell culture. Further development of nonradioactive probes should place virus detection capabilities into the hands of most water quality laboratories.
• Landeen, L. K., Yahya, M. T., & Gerba, C. P. (1989). Efficacy of Copper and Silver ions and reduced levels of free chlorine in inactivation of Legionella pneumophila. Applied and Environmental Microbiology, 55(12), 3045-3050.
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  PMID: 2619303;PMCID: PMC203221;Abstract: Water disinfection systems utilizing electrolytically generated copper and silver ions (200 and 20, 400 and 40, or 800 and 80 μg/liter) and low levels of free chlorine (0.1 to 0.4 mg/liter) were evaluated at room (21 to 23°C) and elevated (39 to 40°C) temperatures in filtered well water (pH 7.3) for their efficacy in inactiviting Legionella pneumophila (ATCC 33155). At room temperature, a contact time of at least 24 h was necessary for copper and silver (400 and 40 μg/liter) to achieve a 3-log10 reduction in bacterial numbers. As the copper and silver concentration increased to 800 and 80 μg/liter, the inactivation rate significantly (P ≤ 0.05) increased from K = 2.87 x 10-3 to K = 7.50 x 10-3 (log10 reduction per minute). In water systems with and without copper and silver (400 and 40 μg/liter), the inactivation rates significantly increased as the free chlorine concentration increased from 0.1 mg/liter (K = 0.397 log10 reduction per min) to 0.4 mg/liter (K = 1.047 log10 reduction per min). Compared to room temperature, no significant differences were observed when 0.2 mg of free chlorine per liter with and without 400 and 40 μg of copper and silver per liter was tested at 39 to 40°C. All disinfection systems, regardless of temperature or free chlorine concentration, showed increase inactivation rates when 400 and 40 μg of copper and silver per liter was added; however, this trend was significant only at 0.4 mg of free chlorine per liter.
• Landeen, L. K., Yahya, M. T., Kutz, S. M., & Gerba, C. P. (1989). Microbiological evaluation of copper: Silver disinfection units for use in swimming pools. Water Science and Technology, 21(3), 267-270.
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  Abstract: The bactericidal effects of electrolytically generated copper:silver ions on pathogenic bacteria of concern in swimming pools, hot tubs and cooling towers were evaluated in disinfection experiments. Copper:silver ion concentrations generated in well water were 400:40 μg/L, respectively. Pure cultures of Legionella pneumophila, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Streptococcus faecalis, were individually tested in water containing copper:silver ions alone, copper:silver ions with free chlorine, and free chlorine alone. Greater numbers of organisms were killed after exposure to copper:silver ions with 0.2 mg/L free chlorine than in either the copper:silver ions or free chlorine alone. L. pneumophila showed greater than a 5 log10 reduction in numbers after 7 minutes exposure to copper:silver ions with 0.2 mg/L free chlorine. In comparison, less than a 2 log10 decrease was obtained after exposure to free chlorine alone. Additional study results are discussed.
• Postillion, F. G., Esposito, D. M., Rusin, P. A., Sinclair, N. A., & Gerba, C. P. (1989). Bacterial fingerprinting to trace source of coliform bacteria during artificial recharge. Array, 220-224.
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  Abstract: This report describes the use of a bacterial 'fingerprint' technique to determine if treated effluent from infiltration beds was the source of coliform bacteria in a nearby well used for drinking water. Phage typing of bacteria is a method which has been used in hospitals to trace the source of infections, since each source usually has a characteristic phage type. Fecal coliform bacteria isolated from local wastewater infiltration basins, a nearby septic tank, and the contaminated well were phage typed. The typing indicated that there was a 17% similarity between the septic tank and the contaminated well, and a 27% similarity was found between the septic tank and the infiltration bed isolates. Finally there was a 52% similarity between the percolation bed isolates and the well isolates. Additional aspects of the subject are discussed.
• Rose, J. B., Landeen, L. K., Riley, K. R., & Gerba, C. P. (1989). Evaluation of immunofluorescence techniques for detection of Cryptosporidium oocysts and Giardia cysts from environmental samples. Applied and Environmental Microbiology, 55(12), 3189-3196.
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  PMID: 2694962;PMCID: PMC203245;Abstract: Cryptosporidium and Giardia species are enteric protozoa which cause waterborne disease. The detection of these organisms in water relies on the detection of the oocyst and cyst forms or stages. Monoclonal and polyclonal antibodies were compared for their abilities to react with Giardia cysts and Cryptosporidium oocysts after storage in water, 3.7% formaldehyde, and 2.5% potassium dichromate, upon exposure to bleach, and in environmental samples. Three monoclonal antibodies to Cryptosporidium parvum were evaluated. Each test resulted in an equivalent detection of the oocysts after storage, after exposure to bleach, and in environmental samples. Oocysts levels declined slightly after 20 to 22 weeks of storage in water, and oocyst fluorescence and morphology were dull and atypical. Oocyst counts decreased after exposure to 2,500 mg of sodium hypochlorite per liter, and fluorescence and phase-contrast counts were similar. Sediment due to algae and clays found in environmental samples interfered with the detection of oocysts on membrane filters. Two monoclonal antibodies and a polyclonal antibody directed against Giardia lamblia cysts were evaluated. From the same seeded preparations, significantly greater counts were obtained with the polyclonal antibody. Of the two monoclonal antibodies, one resulted in significantly lower cyst counts. In preliminary studies, the differences between antibodies were not apparent when used on the environmental wastewater samples. After 20 to 22 weeks in water, cyst levels declined significantly by 67%. Cysts were not detected with monoclonal antibodies after exposure to approximately 5,000 mg of sodium hypochlorite per liter.
• Rose, J. B., Leon, R. D., & Gerba, C. P. (1989). Giardia and virus monitoring of sewage effluent in the state of Arizona. Water Science and Technology, 21(3), 43-47.
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  Abstract: Arizona, located in the arid Southwestern United States, is heavily dependent on groundwater. In order to protect this limited resource, wastewater reuse has been implemented. Virus and Giardia monitoring of wastewater used for irrigation has also been initiated as a means for controlling the public's exposure to these pathogens. Treatment facilities must produce wastewater with no detectable Giardia cysts and one virus plaque forming unit (pfu) per 40 liters (L) for unrestricted reuse. For restricted reuse, 125 pfu/40 L is allowed. Methods based on filtration were used to monitor facilities at monthly, quarterly or biannual frequencies. Results after two years of monitoring are presented. All 11 treatment facilities produced water meeting the virus standard of 125 pfu/40 L. Only plants which used sand filtration and disinfection achieved consistent levels of virus below 1 pfu/40 L. Out of 70 samples, 74% contained no detectable viruses. Giardia was detected in 29 to 50% of the samples. Most plants would need to upgrade their treatment in order to meet standards for unrestricted irrigation.
• Scholze Jr., R. J., Gerba, C. P., Yahya, M. T., & Landeen, L. K. (1989). Technical evaluation of a copper:silver ion swimming pool disinfection unit. Array, 409-416.
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  Abstract: The paper reports on an investigation of a mock swimming pool setup on a laboratory scale. The study used indoor and outdoor simulated swimming pools to compare the efficacy of electrolytically generated copper:silver ions alone and with reduced levels of free chlorine against higher levels of chlorine in reducing numbers of microorganisms. Study results indicated that the addition of electrolytically generated copper:silver ions at the ratio of 400:40 ug/L to simulated swimming pool water allowed the concentration of free chlorine to be reduced while maintaining adequate disinfection for the indoor swimming pools. The outdoor pools showed the best results with the higher level of free chlorine residual, followed by the combination of free chlorine and copper:silver ions.
• Toranzos, G. A., & Gerba, C. P. (1989). An improved method for the concentration of rotaviruses from large volumes of water. Journal of Virological Methods, 24(1-2), 131-140.
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  PMID: 2547811;Abstract: A microporous filter method for the concentration and reconcentration of rotaviruses from large volumes of water was developed. This method allows for the processing of large volumes of water with high recoveries of rotaviruses. Averages of 49% and 41% of seeded viruses were recovered from 20 and 400 l of water, respectively. Of the various eluents evaluated, a mixture of 10% tryptose phosphate broth and 3% beef extract at a pH value of 10.0 was found to give the greatest elution efficiency. The use of the positively charged 1MDS filters allowed for the processing of waters without the need for pH adjustments. An overall recovery of 35% was obtained from 400 l when hydroextraction was used as a secondstep concentration procedure. © 1989.
• Yahya, M. T., Landeen, L. K., Forsthoefel, N. R., Kujawa, K., & Gerba, C. P. (1989). Evaluation of potassium permanganate for inactivation of bacteriophage MS-2 in water systems. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, 24(8), 979-989.
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  Abstract: Potassium permanganate (KMnO4) has been as an oxidant for decades to remove and control iron and manganese in surface water supplies. This oxidant was investigated for its ability to inactivate bacteriophage MS-2 and thereby reduce the amount of chlorine required for a 99.99% reduction of virus during drinking water treatment as required by the U.S. Environmental Protection Agency's Surface Treatment Rule (U.S. EPA 1989). Experiments were conducted in potassium monophosphate buffer (pH 6.0 and pH 8.0) at 7°C. At time intervals from 0 to 30 min, samples were taken and mixed immediately with a solution of sodium thiosulfate:sodium thioglycolate to neutralize residual KMnO4. At 0.5 and 5.0 mg/L KMnO4, results showed no significant differences (p≤0.05) in the inactivation of MS-2 between experiments done at pH 6.0 and those at pH 8.0. Ninety-nine percent of the virus inactivated after 50, 35, and 5 min of exposure time to 0.5, 1.5, and 5.0 mg/L potassium permanganate at pH 8.0, respectively. It appears that at the currently used levels of KMnO4 (up to 10 mg/L), this oxidant may supplement high levels of chlorination in the disinfection of water systems.
• Yayha, M. T., Kutz, S. M., Landeen, L. K., & Gerba, C. P. (1989). Swimming pool disinfection: An evaluation of the efficacy of copper: Silver ions. Journal of Environmental Health, 51(5), 282-285.
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  Abstract: Electrolytically generated copper:silver ions were evaluated as an alternative disinfectant to high levels of chlorination in swimming pools. Pure cultures of Escherichia coli and Streptococcus faecalis were individually tested by inoculating autoclaved well water (containing 460 ug/L copper and 75 ug/L silver) with and without 0.20 mg/L free chlorine. Copper:silver ions in combination with free chlorine reduced bacterial numbers more rapidly than chlorine or copper:silver ions alone. Numbers of S. faecalis also were reduced more in the combined system than in the system containing only free chlorine when exposed for 0.5 min. The addition of copper:silver ions allowed concentrations of free chlorine to be reduced to 0.20 mg/L while still being able to meet guidelines for swimming pool disinfectants.
• Gerba, C. P., & Goyal, S. M. (1988). Enteric virus: Risk assessment of ocean disposal of sewage sludge. Water Science and Technology, 20(11-12), 25-31.
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  Abstract: Densely populated coastal regions of the world generate large quantities of domestic sewage sludge which is often disposed into the marine environment. Present in these wastes are human pathogenic viruses which are capable of surviving for prolonged periods of time in the marine environment and transmitting disease to humans by a number of potential routes of which swimming and consumption of marine foods are the most significant. Hepatitis A virus and Norwalk virus outbreaks associated with shellfish consumption continue to occur in the United States. Three separate epidemiological studies have also shown an association between shellfish consumption and increased risk of hepatitis A infection in consumers. An epidemiological association between non-A and non-B hepatitis has also been demonstrated. A review of the risks of infection, clinical illness and mortality associated with enteroviruses suggests that the presence of these viruses in shellfish and bathing waters presents a significant risk to the consumer.
• Gerba, C. P., Hou, K., & Sobsey, M. D. (1988). MICROBIAL REMOVAL AND INACTIVATION FROM WATER BY FILTERS CONTAINING MAGNESIUM PEROXIDE.. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, A23(1), 41-58.
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  Abstract: Microporous filters containing MgO//2 were shown to be effective in the removal and inactivation of bacteria and viruses from tapwater. Pseudomonas aeruginosa, P. cepacia and Escherichia coli collected by the filters were found to rapidly decrease in numbers to undetectable levels within 24 hours. In contrast, the same bacteria collected on identical filters not containing MgO//2, either rapidly increased in numbers or their numbers remained unchanged. Poliovirus type 1, Echovirus type 1, Reovirus type 3 and Rotavirus SA-11 were found to readily adsorb to the filters. No significant inactivation of bacteria or viruses occurred in tapwater passed through the filters, strongly suggesting that the microorganisms were being inactivated while adsorbed to the filters and not by substances released by the filters into the water. Additional aspects of the subject are discussed.
• Gerba, P., Margolin, B., & Trumper, E. (1988). Enterovirus detection in water with gene probes. Zeitschrift fur die Gesamte Hygiene und Ihre Grenzgebiete, 34(9), 518-519.
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  PMID: 2850671;Abstract: Water virology has long aimed at the goal of the development of rapid and low cost methods for the detection of enteric viruses in water. Gene probes are small pieces of nucleic acid (either DNA or RNA) that hybridize to the complementary base pairs of specific genes and can be used to identify the genetic material of any organism. We report the development of cDNA probes against poliovirus and hepatitis A virus labeled with 32PdATP and 32PdCTP which is capable of detecting as little as one fg of nucleic acid or one tissue culture infective dose of poliovirus or one radio-immuno-focus unit of hepatitis A virus within 72 hours.
• Hou, K., Webster, T. J., & Gerba, C. P. (1988). Microporous filters with oxidizing power for iron and manganese removal from water. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, 23(5), 483-496.
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  Abstract: This report describes the development of a microporous filter carrying oxidizing power to convert the ionic species in water from soluble form, such as Fe+2 and Mn+2, to insoluble form, thus allowing for their continuous removal in one step. The filters were constructed with a cellulosic fiber network for immobilizing adsorbent particles carrying oxidizing power. The porosity of the filters was controlled by selecting the proper size of the binding fibers and the adsorbent. A number of substances were incorporated into the filter matrix and tested for their ability to remove soluble iron from water. Magnesium peroxide was found to be the most effective and was capable of removing significant quantities of iron from water at high flow rates. Removal is believed to take place by a combination of ferric ion adsorption, oxidation to insoluble ferrous hydroxide and filtration. Construction of filter cartridges demonstrated the effectiveness of the material for home water purification.
• Kutz, S. M., & Gerba, C. P. (1988). Comparison of virus survival in freshwater sources. Water Science and Technology, 20(11-12), 467-471.
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  Abstract: Enteric viruses are a potential cause of human gastroenteritis. Their ability to cause waterborne disease may be attributed to their low infectious dose and survival for prolonged periods of time in aquatic environments. Virus survival studies have shown temperature to be a major factor in determination of inactivation rates. Literature on virus inactivation rates at various temperatures was compiled for freshwater sources including ground, tap, river, and impounded water. Data were grouped according to either virus type or water source. Linear regression and analysis of variance were used to evaluate the significance of temperature on virus survival. Data were also analyzed to obtain a general line of best fit for virus inactivation at various temperatures. Temperature was found to be a significant factor in virus inactivation. However, significance of the effect of temperature varied with virus type and water source. Approximately 3 to 99% of variation in virus inactivation rates can be explained by temperature. The slowest inactivation rate obtained was for coliphage in ground water. Inactivation rates for virus in tap water were among the highest and the overall mean inactivation rate for all virus data was slightly greater than 0.5 log per day. Future comparisons of the effect of temperature as well as other environmental factors on virus survival may require the development of standard methods for virus inactivation studies.
• Richardson, K. J., Margolin, A. B., & Gerba, C. P. (1988). A novel method for liberating viral nucleic acid for assay of water samples with cDNA probes. Journal of Virological Methods, 22(1), 13-21.
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  PMID: 2848856;Abstract: Rapid and sensitive methods are needed for the detection of enteric viruses to ensure proper drinking water quality. Gene probes have been shown to be useful for this purpose. Previously, samples to be assayed were treated with a series of phenol-chloroform extractions to release the viral nucleic acid. We have developed a more rapid procedure for liberating or exposing the genome of poliovirus for probing. In this study, a poliovirus model was used to test the ability of heat (65°C for 30 min) for release or exposure of viral nucleic acid. Several different RNase inhibitors were tested for their ability to prevent viral RNA degradation. A comparison of the two methods indicates phenol-chloroform extraction is not necessary before probing. In addition to saving 2-4 h of time, maximum sensitivity levels were consistently obtained using this novel procedure. © 1988.
• Rose, J. B., Darbin, H., & Gerba, C. P. (1988). Correlations of the protozoa, Cryptosporidium and Giardia, with water quality variables in a watershed. Water Science and Technology, 20(11-12), 271-276.
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  Abstract: A watershed in the western United States was surveyed biweekly for a year for the protozoa Cryptosporidium and Giardia. Parasite samples were collected using filtration of 200-1000 L of water, eluted by washing the filter, concentrated and clarified with density gradients. Oocysts and cysts were detected using monoclonal antibodies, in a direct or indirect immunofluorescent assay. The organisms were enumerated on membrane filters using epi-fluorescent microscopy. Number of organisms per liter of water were then calculated. Grab samples were analyzed for total and fecal coliform concentrations as well as turbidities. After log10 (y+1.0) transformations, Pearson's correlation coefficients were derived for each variable against all others. From 39 samples, Cryptosporidium and Giardia were detected in 20 and 12 of the samples, respectively, and oocyst concentrations were approximately 10 times higher than cyst levels. The river downstream from the lake ran through an area concentrated with cattle pasture and had the greater numbers of both parasites (1.09 oocysts and 0.22 cysts/L). The lake, although receiving sewage effluents, may have also had lower levels (0.58 oocysts and 0.08 cysts/L) because of dilution and sedimentation. Coliform levels ranged from 0.12 to 75 CFU/100 ml while fecal coliform levels were slightly lower. Turbidity averaged 55 NTU at the river and 48 NTU at the lake. Correlation coefficients were derived for all variables. Giardia concentrations were significantly correlated to Cryptosporidium concentrations with an r value of 0.778, significant at the 99% confidence level. No other correlations were observed between Giardia and total or fecal coliforms or turbidities nor between Cryptosporidium levels and total or fecal coliforms or turbidities. Neither bacterial indicator organisms nor turbidity are reliable predictors for the absence of enteric protozoa in the study watershed.
• Thurman, R. B., & Gerba, C. P. (1988). Characterization of the effect of aluminum metal on poliovirus. Journal of Industrial Microbiology, 3(1), 33-38.
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  Abstract: Metallic aluminum has been studied for possible use in conjunction with or as an alternative to conventional soluble disinfectants as applied to drinking and wastewater.Acid-washed aluminum was incubated with [35S]methionine-labeled poliovirus type 1 (LSc) and the counts per min (cpm)/plaque-forming units (pfu) ratio was determined. After 2 h, only 0.013% of the cpm remained in solution, indicating viral adsorption onto the surface of the aluminum. After 76 h, 93% of the cpm returned to solution, while infectivity dropped from 2.2 x 107 pfu/ml to undetectable levels. This suggests that infectious viruses were adsorbed onto the aluminum surface and released from the surface of the aluminum as non-infectious particles. Analysis by electron microscopy, cesium chloride gradient and polyacrylamide gel electrophoresis indicates that either dissociation or destruction of the viral capsid proteins occurs during incubation with aluminum, which results in viral inactivation.
• Thurman, R. B., & Gerba, C. P. (1988). Molecular mechanisms of viral inactivation by water disinfectants.. Advances in Applied Microbiology, 33, 75-105.
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  PMID: 3135703;
• Thurman, R. B., & Gerba, C. P. (1988). The molecular mechanisms of copper and silver ion disinfection of bacteria and viruses. Critical Reviews in Environmental Control, 18(4), 295-315.
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  Abstract: Disinfection due to copper or silver ions may result from action at the cell or capsid protein surface or on the nucleic acid of cell or viruses. Metals may alter enzyme structure and function or facilitate hydrolysis or nucleophilic displacement. The means by which cells may reduce the toxic effect of metal ions include: biomethylation, complexation with metallothionen, development of efflux pumps, the binding of metal ions to cell surfaces, and the removal of metal ions by precipitation. The phenomenon of 'multiplicity of reactivation' may reduce the effect of a disinfectant on a virus by allowing a clump of partially inactivated viruses to produce a productive infection in a susceptible cell. Conditions which may effect metal ion-biomolecule interaction include: pH, ionic strength, temperature, dissolved oxygen, presence of interfering substances or light, the chemical form and valency of the metal ion, and the condition of the microorganisms.
• Thurman, R. B., Margolin, A. B., Rockow, J. P., Janauer, G. E., Costello, M. J., & Gerba, C. P. (1988). Characterization of the interaction between viruses and a solid polymeric contact disinfectant. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, 23(5), 405-423.
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  Abstract: The interaction between three different viruses and a sparingly soluble polymeric contact disinfectant was characterized under a variety of conditions. It was found that pH, turbidity, resin concentration, temperature and type of virus determined the degree of virus adsorption onto Resin 14 (a chloromethylated crosslinked polystyrene aminated with N,N dimethyltetradecylbenzyl). Numerous methods were evaluated to recover the adsorbed viruses. However, only a small percentage of the total virus adsorbed could be recovered, as determined by infectivity and radioactively labeled virus. While viruses are effectively retained by the resin, there was no evidence that they were inactivated. The recovery of infectious particles after the elution of viruses, which had adsorbed onto Resin 14, suggests that viral inactivation on the resin surface is not significant.
• Toranzos, G. A., Gerba, C. P., & Hanssen, H. (1988). Enteric viruses and coliphages in Latin America. Toxicity Assessment, 3(5), 491-510.
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  Abstract: Drinking and other types of waters in three Latin American countries were sampled for the presence of enteroviruses, rotaviruses, and coliphages. Large volumes of water and sewage were concentrated using a positively charged filter for the detection of enteric viruses. Statistical analyses indicated no correlation between the presence or absence of fecal coliforms, total coliforms, fecal streptococci, and viruses. Total coliforms and fecal streptococci were isolated in large numbers from pristine tropical rain forest streams, but no enteric viruses were detected in any of the same samples. All streams contaminated with sewage contained enteric viruses and high levels of indicator bacteria. These results indicate that at the present time there is no reliable indicator of the presence of viruses in waters. The presence of coliphages in waters seemed associated with fecal contamination. The large numbers of fecal streptococci and coliforms (both fecal and total) present in the waters sampled may not necessarily indicate that these waters are contaminated with fecal waste.
• Gerba, C. P., & Goyal, S. M. (1987). RISK ASSESSMENT OF ENTERIC VIRUS DISEASE TRANSMISSION BY SHELLFISH CONSUMPTION.. Oceans Conference Record (IEEE), 1757-1760.
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  Abstract: Three separate epidemiological studies have shown an epidemiological association between shellfish consumption and increased risk of hepatitis A infection in consumers. An epidemiological association between non-A and non-B hepatitis has been demonstrated. A review of the risks of infection, clinical illness, and mortality associated with enteroviruses suggest that the presence of these viruses in shellfish presents a significant risk to the consumer.
• Madore, M. S., Rose, J. B., Gerba, C. P., Arrowood, M. J., & Sterling, C. R. (1987). Occurrence of Cryptosporidium oocysts in sewage effluents and selected surface waters.. Journal of Parasitology, 73(4), 702-705.
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  PMID: 3625424;Abstract: An existing method for the detection of Cryptosporidium oocysts in water was modified to investigate oocyst prevalence in large volumes of water. Surface waters and sewage effluents were filtered, eluted from the filter, and concentrated using centrifugation. The resultant pellet was then homogenized, sonicated, and placed on a sucrose gradient to separate oocysts from the sediment. The uppermost gradient layer was then examined by immunofluorescence using a labeled monoclonal antibody. Using this technique, average numbers of oocysts detected in raw and treated sewage were 5.18 X 10(3) and 1.30 X 10(3)/L, respectively. Filtered sewage effluents had significantly lower numbers of oocysts (10.0/L). These data show that sand filtration may reduce the concentrations of this parasite in waste waters. Highly variable oocyst numbers were encountered in surface waters. Since Cryptosporidium oocysts are frequently present in environmental waters, they could be responsible for waterborne outbreaks of disease.
• Margolin, A. B., Bitrick, M. S., DeLeon, R., & Gerba, C. P. (1987). APPLICATION OF GENE PROBES TO POLIOVIRUS AND HEPATITIS A VIRUS DETECTION IN WATER AND SHELLFISH.. Oceans Conference Record (IEEE), 1746-1751.
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  Abstract: The authors have developed cDNA probes for poliovirus type 1 and hepatitis A virus labeled with both **3**2P dATP and dCTP which are reported to be capable of detecting as little as one femtogram of nucleic acid, one tissue culture infectious dose of poliovirus type 1 or one radio-immuno-focus unit of hepatitis A virus. Results are obtained within 72 hours as cell culture is not necessary. The authors have successfully applied this method to the detection of enteroviruses in both water and shellfish concentrates.
• Musial, C. E., Arrowood, M. J., Sterling, C. R., & Gerba, C. P. (1987). Detection of Cryptosporidium in water by using polypropylene cartridge filters. Applied and Environmental Microbiology, 53(4), 687-692.
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  PMID: 3579277;PMCID: PMC203737;Abstract: Members of the genus Cryptosporidium are protozoan parasites that cause gastroenteritis in humans and animals and appear to be spread largely by the fecal-oral route. A method was developed for the concentration and detection of Cryptosporidium oocysts in water to assess their occurrence in the environment and potential for waterborne disease transmission. This method was developed by using spun polypropylene cartridge filters. Optimal conditions for concentration, filter elution, filter porosity, and detection were determined. Fluoresceinated monoclonal antibodies were used for oocyst detection. Experiments also were conducted to study the effect of flow rate, low oocyst numbers, and the addition of detergents on recovery and retention of oocysts. The method that was developed was sensitive enough to detect oocysts at levels of less than 1 per liter. Using this method, we isolated Cryptosporidium oocysts from secondarily treated sewage.
• Rose, J. B., Mullinax, R. L., Singh, S. N., Yates, M. V., & Gerba, C. P. (1987). Occurrence of rotaviruses and enteroviruses in recreational waters of Oak Creek, Arizona. Water Research, 21(11), 1375-1381.
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  Abstract: Recent epidemiological studies have shown a relationship between swimming in recreational waters meeting bacteriological standards and gastroenteritis with a suggested viral etiology. No previous studies have been conducted in the United States on the occurrence of human pathogenic enteric viruses in freshwater recreational areas. The presence of enteroviruses and rotaviruses was investigated in Oak Creek, Arizona, a heavily used recreational area. Water samples were filtered through positively charged filters, eluted with beef extract, and assayed for human enteroviruses and rotaviruses. Eighteen of the 41 recreational water samples were positive for enterovirus or rotavirus. Of these, nine samples exceeded the Arizona State recommended limit of 1 PFU 40 l** minus **1 for full body contact in effluent dominated recreational waters. Several virus positive samples met the recommended fecal coliform standards (200 CFU 100 ml** minus **1) for recreational waters indicating the inadequacy of bacterial standards for monitoring viral water quality.
• Thurman, R. B., & Gerba, C. P. (1987). PROTECTING GROUNDWATER FROM VIRAL CONTAMINATION BY SOIL MODIFICATION.. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, A22(4), 369-388.
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  Abstract: During land application of domestic wastewater, pathogenic enteric viruses may gain entrance into groundwater. Soil modification to enhance virus removal as a method of groundwater protection is described. Inorganic substances were added to a column of sandy loam to assess their ability to enhance the removal of coliphage MS-2 and poliovirus from tapwater and secondarily treated sewage. Aluminum metal, magnesium oxide and magnesium peroxide when added to the soil were found to significantly enhance virus removal above that observed in control columns.
• Yates, M. V., Yates, S. R., Wagner, J., & Gerba, C. P. (1987). Modeling virus survival and transport in the subsurface. Journal of Contaminant Hydrology, 1(3), 329-345.
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  Abstract: The significance of viruses as agents of waterborne disease in the United States is just beginning to be recognized. The ability to predict how far viruses can be transported and how long they can remain infective in soil and groundwater is desirable from the standpoint of planning the placement of sources of contamination so that they will not have an impact on drinking-water wells. This, in turn should have the effect of decreasing the number of waterborne disease outbreaks caused by viruses. This article reviews the factors that affect the survival and migration of viruses in soils and groundwater. It also discusses the efforts that have been made to mathematically model the movement of viruses in the subsurface, including the assumptions made by the modelers. At this time, it appears that modeling efforts are constrained by a lack of quantitative information on virus interactions with soil and fluid media, rather than on mathematical solution techniques. © 1987.
• Gerba, C. P., Rose, J. B., DeLeon, R., Toranzos, G. A., Singh, S. N., & Keswick, B. H. (1986). ISOLATION OF ROTA- AND ENTERO-VIRUSES FROM THREE DRINKING WATER SUPPLIES.. Proceedings - AWWA Water Quality Technology Conference, 451-459.
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  Abstract: In this study the finished water from three different drinking water treatment plants was examined for rota- and enteroviruses. From this and other recent studies it appears that enteric viruses can occur at detectable levels in finished drinking water meeting current coliform (1/100 ml) and turbidity standards (1. 0 NTU) and containing of free chorine ( greater than 0. 2 mg/l). The isolation of human enteric viruses in these waters is not a condemnation of conventional drinking water treatment, but an indication that water quality parameters currently accepted to ensure the production of microbially-safe water does not necessarily ensure the absence of enteric viruses.
• Leon, R. D., Payne, H. A., & Gerba, C. P. (1986). Development of a method for poliovirus detection in freshwater clams. Food Microbiology, 3(4), 345-349.
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  Abstract: Consumption of shellfish has been implicated in more than 100 viral gastroenteritis and hepatitis A outbreaks in the United States. Methods for virus detection in marine shellfish have been recently developed. However recent interest in the establishment of freshwater clam fisheries requires the development of methods capable of detecting viral contamination in these species. In this study, freshwater clam homogenates were seeded with poliovirus and detection efficiencies were determined by the adsorption-elution method. Adsorption of poliovirus to clam homogenates was >99·9% at pH 4·5. Recovery efficiency using elution conditions of pH 9·5 and 8000 mg l-1 sodium chloride averaged 55%. Addition of 3% beef extract to the eluent increased overall recoveries to 83%. In summary, the recovery of seeded poliovirus from freshwater clams requires the same basic methodology used for marine species with minor modifications. © 1986.
• Margolin, A. B., Hewlett, M. J., & Gerba, C. P. (1986). USE OF A cDNA DOT-BLOT HYBRIDIZATION TECHNIQUE FOR DETECTION OF ENTEROVIRUSES IN WATER.. Proceedings - AWWA Water Quality Technology Conference, 87-95.
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  Abstract: Between 1946 and 1980, enteric viruses were identified as a cause in approximately 12% of the waterborne disease outbreaks in the United States. Currently epidemiological evidence for waterborne transmission of human enteric viruses is limited to hepatitis A virus (enterovirus type 72), Norwalk virus, rotavirus, and the Snow Mountain agent. The difficulty in the isolation of many enteric viruses from clinical and water samples probably accounts for the limited number of outbreaks so far identified as causes of waterborne disease. Recently in our laboratory, we have developed a cDNA probe which is labelled with both **3**2P dATP and dCTP. It is capable of detecting as little as 1 fg of nucleic acid or 1 tissue culture infectious dose of poliovirus type 1. This is the most sensitive non-tissue culture technique ever developed for enteroviruses.
• Rose, J. B., Cifrino, A., Madore, M. S., Gerba, C. P., Sterling, C. R., & Arrowood, M. J. (1986). DETECTION OF CRYPTOSPORIDIUM FROM WASTEWATER AND FRESHWATER ENVIRONMENTS.. Water Science and Technology, 18(10), 233-239.
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  Abstract: The method developed for detection of Cryptosporidium in water including: 1) filtration with polypropylene cartridge filters, 2) elution with Tween 80/detergent, 3) concentration with Sheather's flotation, and 4) detection on membrane filters, was evaluated and used to examine wastewater and fresh water for Cryptosporidium cocyst concentrations. Recovery from the sucrose gradient step averaged 72-82%. Overall recovery efficiencies ranged from 25-82% (average 50%), but were diminished with low seeds. Concentrations were found in ranges from 60 to 52,000 oocysts/gal in treated and raw sewage. In fresh water, oocysts numbered 8 to 22,000/gal and were concentrated in rapid sand filters averagingb 59,000/gal in the backflush. Cryptosporidium may now be considered a potential waterborne parasite.
• Rose, J. B., Gerba, C. P., Singh, S. N., Toranzos, G. A., & Keswick, B. (1986). ISOLATING VIRUSES FROM FINISHED WATER.. Journal / American Water Works Association, 78(1), 56-61.
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  Abstract: Reduction of enteroviruses and rotaviruses averaged 81 and 93 percent, respectively, at a full-scale 205-mgd (776-ML/d) plant whose treatment train includes chemical flocculation, sand filtration, and chlorination. The highest reduction of enteroviruses occurred during prechlorination-flocculation and filtration, whereas the highest reduction of rotaviruses occurred during prechlorination-clarification and final chlorination. Enteroviruses or rotaviruses occurred in 24 percent of the finished water samples, which had greater than 0. 2 mg free chlorine/L and met coliform bacteria (1/100 mL) and turbidity (1 ntu) standards. Although major plant deficiencies may have been responsible for the occurrence of viruses in the finished water, the results of this study indicate that finished water, with measurable levels of free residual chlorine and meeting standards for coliform bacteria and turbidity, cannot be assumed to be virus free.
• Rose, J. B., Musial, C. E., Arrowood, M. J., Sterling, C. R., & Gerba, C. P. (1986). DEVELOPMENT OF A METHOD FOR THE DETECTION OF CRYPTOSPORIDIUM IN DRINKING WATER.. Proceedings - AWWA Water Quality Technology Conference, 117-125.
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  Abstract: The volume and quality of the water filtered greatly influenced the overall recovery of the method. Increased organic matter and sediment more than likely interferes with recovery of the oocysts from the filter, recovery after sheather's flotation and detection. Still it is significant that naturally occurring Cryptosporidium could be isolated from secondary effluent using this method and rough estimates gave a concentration of five to 17 oocysts per liter. This recent finding illustrates the necessity for further investigation of Cryptosporidium. Further improvements are needed for filtration-elution method for concentration of Cryptosporidium oocysts.
• Singh, S. N., Bassous, M., Gerba, C. P., & Kelley, L. M. (1986). Use of dyes and proteins as indicators of virus adsorption to soils. Water Research, 20(3), 267-272.
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  Abstract: Outbreaks of viral diseases have been associated with contamination of ground water sources by viral migration from septic tanks. A better understanding of virus adsorption to soils might help elucidate the possible mechanism of subsurface virus migration and ultimate contamination of ground water sources. The present investigation sought a simple test that could predict virus adsorption to soils. Two dyes, methylene blue (positively charged) and amaranth (negatively charged), and three proteins, ferritin, myoglobin and cytochrome-c, were evaluated as potential indicators of virus adsorption to 20 different soils. The results indicated that no single indicator could predict the adsorption pattern for the different viruses which were evaluated with the soils tested. However, the viruses could be divided into two groups based on their similarities to adsorption of ferritin and cytochrome-c to soils.
• Toranzos, G. A., Hanssen, H., & Gerba, C. P. (1986). Occurrence of enteroviruses and rotaviruses in drinking water in Colombia. Water Science and Technology, 18(10), 109-114.
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  Abstract: Finished drinking water samples were collected at several drinking water plants whose treatment included flocculation, sand filtration and chlorination. Drinking water samples were also collected from the taps of private homes, hotels and community taps. Out of eight samples of finished drinking water leaving the plants studied, three were found to contain enteric viruses. Rotaviruses were detected in two samples and enterovirus in one. Two of the samples containing enteric viruses also contained greater than 100 coliforms/100 ml. Rotaviruses were isolated from three tapwater samples and enteroviruses from one. All the tapwater samples which contained enteric viruses had visible turbidity and also contained coliform bacteria.
• Yates, M. V., Yates, S. R., Warrick, A. W., & Gerba, C. P. (1986). Use of geostatistics to predict virus decay rates for determination of septic tank setback distances. Applied and Environmental Microbiology, 52(3), 479-483.
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  PMID: 3532954;PMCID: PMC203559;
• Badawy, A. S., Gerba, C. P., & Kelley, L. M. (1985). Survival of rotavirus SA-11 on vegetables. Food Microbiology, 2(3), 199-205.
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  Abstract: Survival of rotavirus on lettuce, radishes, and carrots was studied to evaluate the potential of rotavirus transmission by vegetables irrigated with wastewater. The vegetables were contaminated with rotavirus SA-11 and stored at 4°C and room temperature in covered and uncovered containers to simulate post harvest conditions. Virus decay rates were greater on radishes and carrots than lettuce. Decay rates of rotavirus on lettuce, radish, and carrot ranged from -0·057 to -0·479 (log10 pfu/day). Rotavirus SA-11 survived on lettuce, radish, and carrot for 25 to 30 days at 4°C but at room temperature survival was very different for the various vegetables varying from 5 to 25 days. Greatest survival was always observed on the lettuce. These data suggest that rotaviruses can survive long enough on contaminated vegetables as to be transmitted by this vehicle. © 1985.
• Gerba, C. P., & Goyal, S. M. (1985). PATHOGEN REMOVAL FROM WASTEWATER DURING GROUNDWATER RECHARGE.. Artif Recharge of Groundwater, 283-317.
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  Abstract: Many factors control the removal of pathogenic bacteria and viruses during the percolation of sewage through the soil. Although the presence of viruses in groundwater has been demonstrated, it would appear that with proper site selection and management the presence of viruses could be minimized or eliminated. The key is to define the processes involved in the survival and transport of pathogens in groundwater. With proper design, land treatment could be used as an effective method for reducing the number of pathogens in wastewater. With the proper soil type, viruses and bacteria can be reduced to levels as effectively as by chlorination as currently practiced, after the travel of wastewater through only a few centimeters of soil.
• Gerba, C. P., & Hou, K. (1985). Endotoxin removal by charge-modified filters. Applied and Environmental Microbiology, 50(6), 1375-1377.
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  PMID: 3911902;PMCID: PMC238766;Abstract: The effects of positively charged nylon and depth (cellulose-diatomaceous earth) filters on endotoxin removal from various solutions were evaluated. The charged filter media removed significant amounts of Escherichia coli and natural endotoxin from tap water, distilled water, sugars, and NaCl solutions; no significant removal of endotoxin was observed with negatively charged filter media. The extent of removal was influenced by pH, the presence of salts, and organic matter. Such media may be useful for the control of endotoxins in raw-product water of solutions used to prepare parenteral drug products or in other fluids where endotoxin control is desired.
• Gerba, C. P., Rose, J. B., & Singh, S. N. (1985). Waterborne gastroenteritis and viral hepatitis. Critical Reviews in Environmental Control, 15(3), 213-236.
• Keswick, B. H., Gerba, C. P., Rose, J. B., & Toranzos, G. A. (1985). Dectection of rotavirus in treated drinking water. Water Science and Technology, 17(10), 1-6.
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  Abstract: The removal of naturally occurring viruses was studied at a full scale 9m3/sec (205 mgd) water treatment plant. Rotavirus was detected in 41 of 113 large volume samples collected after successive stages of the water treatment process. Virus recovery was highest during the summer rainy season when water quality declined. Rotavirus was recovered from 3 of 26 finished water samples which met acceptable limits for turbidity, total coliform bacteria and residual chlorine. Water from heavily polluted sources which meets water quality guidelines cannot be assumed to be virus free.
• Thurman, R. B., & Gerba, C. P. (1985). GROUNDWATER PROTECTION BY SOIL MODIFICATION.. Array, 105-108.
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  Abstract: Certain soils exhibit a limited capacity for removal of microbes when domestic sewage effluent percolates through the soil. In this study metallic aluminum was added to soil in an attempt to enhance the removal of viruses. Water and sewage containing the bacterial virus MS-2 virus was passed through 20 cm columns of sandy soil to which 5. 0 gm of aluminum was added. The soil columns were flooded in cycles of 7 days flooding and 3 days drying. Modification of the soil by addition of metallic aluminum caused a six to eight log decrease in virus concentration, while control columns with no aluminum showed only a two log decrease. Virus reduction continued in the test columns, with no significant changes, after five weeks of intermittent flooding.
• Wang, D., Gerba, C. P., Lance, J., & Goyal, S. M. (1985). COMPARATIVE REMOVAL OF ENTERIC BACTERIA AND POLIOVIRUS BY SAND SOILS.. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, A20(6), 617-624.
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  Abstract: The removal of poliovirus type 1, coliforms, fecal coliforms and fecal streptococcus from treated sewage was compared in four sandy soils. In all soils, poliovirus removal was substantially greater than that observed for any of the bacterial indicator groups. These results suggest that in soils undergoing rapid infiltration of wastewater, indicator bacteria are conservative indicators of poliovirus removal.
• Yates, M. V., & Gerba, C. P. (1985). Factors controlling the survival of viruses in groundwater. Water Science and Technology, 17(4-5 -5 pt 2), 681-687.
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  Abstract: Groundwater samples collected from throughout the United States were inoculated with the coliphage MS-2 and the rate of virus inactivation determined. All samples were incubated at the temperature of the native groundwater. All samples were analyzed for pH, nitrates, ammonia, turbidity, total dissolved solids, and calcium, magnesium and total hardness. Multiple regression analysis of the chemical variates indicated that temperature and calcium hardness were significantly correlated with the rate of virus die-off. Temperature alone accounts for 60% of the variation in decay rate. Using all variates, 94% of the variation could be predicted.
• Yates, M. V., Gerba, C. P., & Kelley, L. M. (1985). Virus persistence in groundwater. Applied and Environmental Microbiology, 49(4), 778-781.
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  PMID: 4004211;PMCID: PMC238444;Abstract: More than 50% of the outbreaks of waterborne disease in the United States are due to the consumption of contaminated groundwater. An estimated 65% of the cases in these outbreaks are caused by enteric viruses. Little, however, is known about the persistence of viruses in groundwater. The purpose of this study was to determine whether measurable chemical and physical factors correlate with virus survival in groundwater. Groundwater samples were obtained from 11 sites throughout the United States. Water temperature was measured at the time of collection. Several physical and chemical characteristics, including pH, nitrates, turbidity, and hardness, were determined for each sample. Separate water samples were inoculated with each of three viruses (poliovirus 1, echovirus 1, and MS-2 coliphage) and incubated at the in situ groundwater temperature; selected samples were also incubated at other temperatures. Assays were performed at predetermined intervals over a 30-day period to determine the number of infective viruses remaining. Multiple regression analysis revealed that temperature was the only variable significantly correlated with the decay rates of all three viruses. No significant differences were found among the decay rates of the three viruses, an indication that MS-2 coliphage might be used as a model of animal virus survival in groundwater.
• Yates, M. V., Yates, S. R., Warrick, A. W., & Gerba, C. P. (1985). PREVENTING VIRAL CONTAMINATION OF DRINKING WATER.. Array, 117-121.
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  Abstract: The purpose of this study was to predict zones of protection around drinking water wells in an effort to limit ground water contamination from viruses. Seventy-one water samples were collected from wells in the Tucson basin. The samples were inoculated with MS-2 phage and the decay rates of the virus with time were determined. Kriging, a geostatistical method which analyzes data based on its spatial arrangement, was employed to estimate decay rates at point for which no samples were taken using known values obtained at nearby wells. Using the kriged values for virus decay rates and the characteristics of ground water flow in the Tucson basin, a map of the area was constructed which delineates zones around drinking water wells within which potential sources of ground water pollution should not be placed to ensure the absence of viruses in the wells.
• Zerda, K. S., Gerba, C. P., Hou, K. C., & Goyal, S. M. (1985). Adsorption of viruses to charge-modified silica. Applied and Environmental Microbiology, 49(1), 91-95.
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  PMID: 2983608;PMCID: PMC238350;Abstract: The purpose of this study was to provide a clearer understanding of virus adsorption, focusing specifically on the role of electrostatic interactions between virus particles and adsorbent surfaces. The adsorption of poliovirus 1, reovirus types 1 and 3, and coliphages MS-2 and T2 to colloidal silica synthetically modified to carry either positive or negative surface charge was evaluated. Adsorption experiments were performed by combining virus and silica in 0.1-ionic-strength buffers of pH 4.0, 6.4, and 8.5. Samples agitated for specified adsorption periods were centrifuged to pellet adsorbent particles plus adsorbed virus, and the supernatants were assayed for unadsorbed virus. All viruses adsorbed exclusively to negatively charged silica at pH values below their isoelectric points, i.e., under conditions favoring a positive surface charge on the virions. Conversely, all viruses adsorbed exclusively to positively charged silica at pH values above their isoelectric points, i.e., where virus surface charge is negative. Viruses in near-isoelectric state adsorbed to all types of silica, albeit to a lesser degree.
• Deetz, T. R., Smith, E. M., Goyal, S. M., Gerba, C. P., J, J., Tsai, L., DuPont, H. L., & Keswick, B. H. (1984). Occurrence of rota- and enteroviruses in drinking and environmental water in a developing nation. Water Research, 18(5), 567-571.
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  Abstract: Rotaviruses have been implicated as a major cause of childhood and traveler's diarrhea in developing countries. Since water is known to be a vehicle of transmission of other enteric viruses, we sought to determine if water could play a role in the transmission of rotavirus infections in a developing nation by applying recently developed techniques for the concentration of viruses from tapwater and environmental (lake, river, ocean and aqueduct) water in Mexico. In an initial survey during the rainy season in August 1978, rotavirus was detected in 10 of 10 drinking water samples and coxsackie B4 or B6 virus in 5 of 10. In a larger survey during the dry season in December 1979, rotavirus was recovered from 3 and enteric viruses from 8 of 21 drinking water samples. Water quality data, available for the 1979 survey, indicated that while many tapwater samples did not meet U.S. coliform standards, some samples containing infectious virus did. Our data suggest that current bacteriological water quality standards for potable water do not reflect viral contamination. © 1984.
• Gerba, C. P. (1984). Applied and theoretical aspects of virus adsorption to surfaces.. Advances in Applied Microbiology, 30, 133-168.
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  PMID: 6099689;
• Gerba, C. P., Janauer, G. E., & Costello, M. (1984). Removal of poliovirus and rotavirus from tapwater by a quaternary ammonium resin. Water Research, 18(1), 17-19.
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  Abstract: A quaternary ammonium-type anion exchange resin was tested as a contact water viral disinfectant. Suspensions of tapwater containing approx. 104 plaque-forming units ml-1 of poliovirus type 1 and Simian rotavirus SA-11 were passed through 1 ml beds of resin, at flow rates of 10-12 ml min-1. With resin 14-1.91 - > 99.9% of the input virus was removed. The beds were effective in removal of virus even after passage of 1500 ml of tapwater. Less than 10% of the virus associated with resin 14-1 could be recovered as compared to 100% for control resin. Kinetic studies indicated that virus adsorbed to the resins were being inactivated. © 1984.
• Goyal, S. M., Keswick, B. H., & Gerba, C. P. (1984). Viruses in groundwater beneath sewage irrigated cropland. Water Research, 18(3), 299-302.
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  Abstract: The occurrence of enteric viruses in groundwater and soil was examined beneath three different sites where slow rate sewage irrigation of cropland is practiced. At all sites, the sewage was secondarily treated (aeration) before land application. Enteric viruses were isolated from wells beneath all sites. The lowest frequency of isolation was from wells beneath the one site practicing chlorination before application by spray irrigation. Viruses were detected in wells as deep as 27.5 m. © 1984.
• Hejkal, T. W., Smith, E. M., & Gerba, C. P. (1984). Seasonal occurrence of rotavirus in sewage. Applied and Environmental Microbiology, 47(3), 588-590.
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  PMID: 6324678;PMCID: PMC239725;Abstract: A seasonal distribution was observed for rotavirus in sewage by using indirect immunofluorescence. Levels were low from May through September and generally higher during winter and spring. In contrast, no seasonal pattern was observed for total enteroviruses. Limitations of the indirect immunofluorescence assay and enzyme immunoassay for environmental samples are discussed.
• Keswick, B. H., Gerba, C. P., DuPont, H. L., & Rose, J. B. (1984). Detection of enteric viruses in treated drinking water. Applied and Environmental Microbiology, 47(6), 1290-1294.
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  PMID: 6331313;PMCID: PMC240223;Abstract: The occurrence of viruses in conventionally treated drinking water derived from a heavily polluted source was evaluated by collecting and analyzing 38 large-volume (65- to 756-liter) samples of water from a 9 m3/s (205 x 106 gallons [776 x 106 liters] per day) water treatment plant. Samples of raw, clarified, filtered, and chlorinated finished water were concentrated by using the filter adsorption-elution technique. Of 23 samples of finished water, 19 (83%) contained viruses. None of the nine finished water samples collected during the dry season contained detectable total coliform bacteria. Seven of nine finished water samples collected during the dry season met turbidity, total coliform bacteria, and total residual chlorine standards. Of these, four contained virus. During the dry season the percent removals were 25 to 93% for enteric viruses, 89 to 100% for bacteria, and 81% for turbidity. During the rainy season the percent removals were 0 to 43% for enteric viruses, 80 to 96% for bacteria, and 63% for turbidity. None of the 14 finished water samples collected during the rainy season met turbidity standards, and all contained rotaviruses or enteroviruses.
• Lance, J. C., & Gerba, C. P. (1984). Effect of ionic composition of suspending solution on virus adsorption by a soil column. Applied and Environmental Microbiology, 47(3), 484-488.
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  PMID: 16346487;PMCID: PMC239707;Abstract: The effects of various electrolytes on the adsorption of poliovirus was measured in 250-cm-long soil columns with ceramic samplers at different depths. Viruses suspended in deionized water moved much farther through the soil than those suspended in tap water, whereas movement in sewage water was intermediate. The salt content of the tap water and sewage water promoted virus adsorption, but evidently the organic compounds in sewage retarded adsorption. When viruses were suspended in chloride solutions of K+, Na+, Ca+, and Mg2+, virus adsorption increased as the cation concentration and valence increased. The depth of virus penetration was related to the ionic strength of the solutions. Virus penetration data for NO3-, SO42-, and H2PO4- salts of K+, Na+, and Ca2+ indicated that other anions were more effective than Cl- in promoting virus adsorption. Also NH4+ was more effective than other cations in limiting the penetration depth of viruses. It seems that ions composed of radicals are more effective than ions composed of single atoms in promoting virus adsorption. Al3+ was the most effective ion in limiting virus penetration, probably owing to flocculation of the viruses. Adding AlCl3 concentrations to secondary sewage effluent to provide an Al3+ concentration of 0.1 mM reduced the virus penetration depth to 40 cm. These studies show that the ionic composition of the suspending solutions must be considered in predicting virus penetration depths, and it may be practical to add low concentrations of a flocculating agent such as AlCl3 to sewage water to limit virus movement through very porous soils.
• Lance, J. C., & Gerba, C. P. (1984). Virus movement in soil during saturated and unsaturated flow. Applied and Environmental Microbiology, 47(2), 335-337.
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  PMID: 6324673;PMCID: PMC239670;Abstract: Virus movement in soil during saturated and unsaturated flow was compared by adding poliovirus to sewage water and applying the water at different rates to a 250-cm-long soil column equipped with ceramic sampler at different depths. Movement of viruses during unsaturated flow of sewage through soil columns was much less than during saturated flow. Viruses did not move below the 40-cm level when sewage water was applied at less than the maximum infiltration rate; virus penetration in columns flooded with sewage was at least 160 cm. Therefore, virus movement in soils irrigated with sewage should be less than in flooded groundwater recharge basins or in saturated soil columns. Management of land treatment systems to provide unsaturated flow through the soil should minimize the depth of virus penetration. Differences in virus movement during saturated and unsaturated flow must be considered in the development of any model used to simulate virus movement in soils.
• Rose, J. B., Singh, S. N., Gerba, C. P., & Kelley, L. M. (1984). Comparison of microporous filters for concentration of viruses from wastewater. Applied and Environmental Microbiology, 47(5), 989-992.
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  PMID: 6742838;PMCID: PMC240036;
• Toranzos, G. A., Gerba, C. P., & Hanssen, H. (1984). Simple field method for concentration of viruses from large volumes of water. Applied and Environmental Microbiology, 48(2), 431-432.
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  PMID: 6385852;PMCID: PMC241531;
• Zerda, K. S., & Gerba, C. P. (1984). Agarose isoelectrofocusing of intact virions. Journal of Virological Methods, 9(1), 1-6.
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  PMID: 6094606;Abstract: A convenient and accurate method for determining the isoelectric points of intact virions is described. Tritium-labeled poliovirus 1 (strains Brunhilde and LSc-2) and echovirus 1 (isolates V239, V248, V212, R115 and 4CH-1) were successfully focused into sharp bands at their respective isoelectric points using a thin-layer agarose isoelectric focusing system. In situ detection of labeled virus bands in the agarose was by fluorography. Freezing and thawing of virus samples prior to isoelectric focusing did not alter their respective isoelectric points. © 1984.
• Farber, F. E., Gradwohl, S. E., Sanford, P. B., Tobin, M. J., Lee, K. J., & Gerba, C. P. (1983). Bacteriophage concentration from water by filter chromatography. Journal of Virological Methods, 7(5-6), 297-304.
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  PMID: 6677647;Abstract: The efficiency of an electropositive filter for membrane chromatography of viruses was examined using coliform phages T1, T4, lambda and Salmonella phage P22. Phages diluted in dechlorinated tap water were adsorbed to filters at neutral pH and eluted by 3% beet extract in 0.05 M glycine buffer at selected alkaline pH values. With exception of lambda phage, which displayed erratic adsorption behavior at any pH, all bacteriophages studied, adsorbed to filters with an efficiency of 97-100% at pH values ranging between 6.0 and 8.0. Each phage was readily eluted at alkaline pH levels. Maximal elution (86.2%) of T1 phage and lambda phage (79%) occurred at pH 10, while T4 and Salmonella phages were eluted most efficiently at pH 11 at values of 91.7 and 81.9%, respectively. The resolving power of the filter was such that individual phages within the same virus group (T1 and T4 phage) could be eluted at pHs differing by only one unit. © 1983.
• Gerba, C. P. (1983). METHODS FOR RECOVERING VIRUSES FROM THE WATER ENVIRONMENT.. Viral Pollut of the Environ, 19-35.
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  Abstract: The most promising methods and principles to remove viruses from water are considered. Many biochemical procedures used for concentrating and purifying proteins have been explored in the development of methods for concentrating viruses from water. Viruses are largely protein, and methods useful for concentrating macromolecular proteins such as phase partition, immunochemical, precipitation, and adsorption techniques have been applied to the concentration of viruses from water. In practice, many of these methods are highly effective in the laboratory for concentrating viruses, but their application is often limited to use with highly contaminated waters.
• Goyal, S. M., & Gerba, C. P. (1983). Viradel method for detection of rota virus from seawater. Journal of Virological Methods, 7(5-6), 279-285.
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  PMID: 6330146;Abstract: This report describes the use of a virus adsorption-elution (Viradel) technique for the concentration and detection of rotavirus from seawater. Simian rotavirus SA-11 was used as a model virus because it can be readily propagated and plaqued in vitro. The virus adsorbed optimally to fiberglass epoxy filters when seawater was adjusted to pH 3.5 and aluminum chloride added to a concentration of 1.0 mM. Adsorbed virus was eluted with 6% beef extract at pH 10.5 and was further concentrated to a smaller volume by a modification of the organic flocculation method. Using this method, in conjunction with an indirect immunofluorescence test, rotavirus was detected in sewage-contaminated seawater. © 1983.
• Hejkal, T. W., Gerba, C. P., Henderson, S., & Freeze, M. (1983). Bacteriological, virological and chemical evaluation of a wastewater-aquaculture system. Water Research, 17(12), 1749-1755.
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  Abstract: Levels of fecal coliforms (FC), fecal streptococci (FS), Salmonella spp and enteric viruses were monitored in the water, sediment and fish in experimental wastewater-fish ponds near Benton, Arkansas, U.S.A. Concentrations of five heavy metals were also monitored in the fish and wastewater. Concentrations of indicator bacteria were reduced by as much as 99.7% through the series of six ponds which had a calculated total retention time of 72 days. Two filter-feeding species of Chinese carp, Hypophthalmichthys molitrix (silver carp) and Aristichthys nobilis (bighead carp), grown in the last three ponds accumulated FC and FS in their digestive tracts and skin at levels as great or greater than in the surrounding water and sediment. Only low levels of FC and FS were found in the fish muscle tissue (maximum of 25 FS per 100 g) even when concentrations of bacteria in the gut exceeded 105 per 100 g. Concentrations of bacteria in the water and sediment were not good predictors of concentrations in the fish. No Salmonella and no enteric viruses were isolated from the fish, but this lack of isolates was attributed to the extremely low levels which were present in the influent wastewater. Higher levels of copper and mercury were found in the fish flesh than in the surrounding water, with three of eleven fish samples containing higher than acceptable levels of mercury in the edible portion. Based on the efficiency of wastewater treatment, an aquaculture system using silver and bighead carp was judged to be a viable treatment system for domestic sewage resulting in a product suitable for animal or human consumption if proper precautions are taken in harvesting and processing the fish. © 1983.
• Singh, S. N., & Gerba, C. P. (1983). Concentration of coliphage from water and sewage with charge-modified filter aid. Applied and Environmental Microbiology, 45(1), 232-237.
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  PMID: 6337549;PMCID: PMC242259;Abstract: Methods of detecting and concentrating animal viruses from large volumes of water and wastewater have experienced rapid development in recent years, but only a few methods are available for the concentration of bacteriophages. The present study describes the use of a charge-modified (Zeta Plus) filter aid (AMF Cuno, Meriden, Conn.) for the concentration of coliphages from large volumes of water and sewage. Coliphages MS-2 and f2 were efficiently adsorbed from water and sewage to the positively charged filter aid. Elution was accomplished with 4% beef extract -0.5 M CaCl adjusted to pH 9.5. The recovery of f2 from 10- to 20-liter volumes of tap water ranged between 11 and 70%, and the recovery of MS-2 ranged between 43 and 70%. The efficiency of recovery of naturally occurring coliphages from secondarily treated sewage ranged between 16 and 44%. This technique appears to be promising because it requires low-cost equipment (47-mm polypropylene filter housing), is easy to handle, and can filter large volumes of water (≥20 liters) with good recoveries. Filtrations can be conducted at the ambient pH of the water, and the unit cost per filtration (i.e., the cost of filter aid) comes to less than three cents per sampling. The technique could be useful in evaluation of viral water quality, study of the ecology and occurrence of phages in natural waters, and isolation of rare phages from natural waters.
• Singh, S. N., Rose, J. B., & Gerba, C. P. (1983). Concentration of viruses from tap water and sewage with a charge-modified filter aid. Journal of Virological Methods, 6(6), 329-336.
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  PMID: 6309878;Abstract: Positively charged microporous filters have been shown to have definite advantage over negatively charged filters for concentrating viruses from water as they eliminate the need of water conditioning (acidification and multivalent cation addition) prior to filtration. The present study was designed to evaluate the use of a charge-modified (Zeta plus) filter aid (AMF CUNO, Meriden, CT) for the concentration of viruses (Poliovirus-1, Coxsackievirus B-3 and ECHO virus-7) from large volumes of tap water. Charge-modified filter aid could efficiently adsorb polio, coxsackie and ECHO viruses from water. The adsorbed viruses from both tap water and secondary sewage were most efficiently eluted with 4% beef extract - 0.5 M NaCl, pH 9.5. The efficiency of recovery of poliovirus, coxsackievirus and ECHO virus from 10- to 20-1 vols, of tap water ranged between 32 and 98%, 67 and 100% and 69 and 100%, respectively. This technique appears to have distinct advantages over previous methods as it requires low cost equipment (47 mm polypropylene filter housing) and materials, is simple and easy to handle, can filter large volumes of water (≥20 l) with good recoveries at ambient pH and can be efficiently used to monitor viral water quality. © 1983.
• Goyal, S. M., & Gerba, C. P. (1982). Occurrence of endotoxins in groundwater during the land application of wastewater. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, 17(2), 187-196.
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  Abstract: Since sewage may contain high concentrations of bacterial endotoxin, the occurrence of endotoxin in groundwater underlying five sewage land application sites was studied. Endotoxin concentrations were found to range from 0.3 to 480 ng/ml in wells 3 to 37 m beneath these sites. Although these concentrations were higher than the native groundwater, a 90% to 99.9% reduction in endotoxin occurred during percolation of this sewage water through the soil.
• Hejkal, T. W., Gerba, C. P., & Rao, V. C. (1982). Reduction of cytotoxicity in virus concentrates from environmental samples. Applied and Environmental Microbiology, 43(3), 731-733.
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  PMID: 7073280;PMCID: PMC241904;Abstract: The reduction of cytotoxicity in virus concentrates from environmental samples was accomplished by high-speed centrifugation and by filtration of the samples through positively charged depth filters.
• Keswick, B. H., Gerba, C. P., Secor, S. L., & Cech, I. (1982). SURVIVAL OF ENTERIC VIRUSES AND INDICATOR BACTERIA IN GROUNDWATER.. Journal of Environmental Science and Health - Part A Environmental Science and Engineering, A17(6), 903-912.
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  Abstract: The paper reports on a study that compared the ability of several viruses and bacteria to survive in groundwater. The organisms were contained in individual survival chambers and exposed to a continuous flow of groundwater from a 275 ft deep domestic well. The survival of the test organisms ranked in order of decreasing decay rates were coliphage f2, rotavirus SA-11, Escherichia coli, echovirus-1, fecal streptococcus, poliovirus-1, and coxsackievirus B3. Low numbers of bacteria and viruses survived for the 24-day duration of the experiment. These results indicate that enteric viruses are capable of surviving for extended periods in groundwater.
• LaBelle, R., & Gerba, C. P. (1982). Investigations into the protective effect of estuarine sediment on virus survival. Water Research, 16(4), 469-478.
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  Abstract: It has been shown that enteric viruses readily adsorb to estuarine sediments and that this association acts to prolong their survival in marine waters. This study sought to ascertain whether sediment protects virus from any one specific inactivating factor and to define the properties of sediment responsible for such protection. Laboratory studies demonstrated that sediment was capable of protecting poliovirus 1 (strain LSc) from the inactivating effects of microorganisms, heat and salts. An anaerobic environment did not influence virus survival. The presence of bacterial nutrients was found to enhance virus survival, possibly by virus adsorption to the resulting bacterial population; however, organic material naturally present in sediment did not enhance virus survival in sea-water. Virus adsorption to sediment appears to be the most important characteristic of the virus and sediment interaction that retards virus inactivation. © 1982.
• Lance, J. C., Gerba, C. P., & Wang, D. S. (1982). Comparative movement of different enteroviruses in soil columns. Journal of Environmental Quality, 11(3), 347-351.
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  Abstract: Echo 1 and Echo 29, the least adsorptive viruses studied in previous batch studies with small soil samples, and Polio 1 were seeded in secondary sewage effluent that was applied to 250-cm-long soil columns. Water samples from various column depths showed that the adsorption patterns for Echo 29 and Polio 1 were quite similar. Fewer Echo 1 viruses were adsorbed near the soil surface, bu the leaching pattern below the 40-cm depth resembled that for Polio 1 and Echo 29. The leaching patterns of Echo 1 and Polio 1 were influenced in a similar manner by changes in virus concentration, and flow velocity and leaching patterns were similar for three other soils with a wide range in virus-retention efficiencies. These tests and previous experiments on virus adsorption and survival suggest that movement of polioviruses type 1 through soils is similar to the movement of many other enteroviruses through soils. Virus movement through loamy sand roughly paralleled that of fecal coliforms.
• Melnick, J. L., & Gerba, C. P. (1982). Viruses in surface and drinking waters. Environment International, 7(1), 3-7.
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  Abstract: Over 114 different human enteric viruses are known. They are all excreted into sewage, and opportunities exist for them to find their way into water distribution systems. The characteristics of the illnesses caused by enteric viruses make their transmission by water difficult to recognize. Methods are not available for isolating all of the enteric viruses from water, so that finding any type of human virus in drinking water is an indication that other types may also be present. With improvements in technology, our laboratory has recently been able to detect group B coxsackieviruses, rotaviruses, and hepatitis A virus in chlorinated drinking water. At present, there are no uniform methods for concentrating, isolating, and identifying viruses in water. Emphasis should be placed on seeking uniformity in methods so that standards can be set for viruses in water. © 1982.
• Schaiberger, G. E., Edmond, T. D., & Gerba, C. P. (1982). Distribution of enteroviruses in sediments contiguous with a deep marine sewage outfall. Water Research, 16(9), 1425-1428.
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  Abstract: The distribution of enteroviruses, coliforms, fecal coliforms and fecal streptococcus discharged from a raw sewage outfall pipe 3.6 km from shore at a depth of 44 m was studied. Enteroviruses and indicator bacteria were only isolated from water in an area within 200 m of the outfall. However, viruses were isolated from sediments as far as 3.6 km from the outfall at recreational bathing beaches. The concentration of enteroviruses in the sediment at the outfall boil ranged from 112 to 78 PFU l-1 and 0 to 30 PFU l-1 at the bathing beach. Indicator bacteria were not detected in the water or sediment at the bathing beach. Analysis of sediments for viruses may give a better idea of the long term distribution of sewage discharged from the outfall pipe. © 1982.
• Smith, E. M., & Gerba, C. P. (1982). Development of a method for detection of human rotavirus in water and sewage. Applied and Environmental Microbiology, 43(6), 1440-1450.
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  PMID: 6285825;PMCID: PMC244252;Abstract: The simian rotavirus SA11 was used to develop a simple, reliable, and efficient method to concentrate rotavirus from tap water, treated sewage, and raw sewage by absorption to and elution from Filterite fiberglass-epoxy filters. SA11 adsorbed optimally to Filterite filters from water containing 0.5 mM AlCl3 at pH 3.5. Filterbound virus was eluted with 0.05 M glycine-NaOH supplemented with 10% tryptose phosphate broth at pH 10. SA11 was quantitated by plaque assay, whereas human rotavirus was detected by immunofluorescence. The method was applied to detect rotavirus in raw and treated sewage at two Houston, Tex., sewage treatment plants. The sewage isolates were identified as rotavirus, probably a human strain, based on several criteria. The sewage isolates were detectable by an immunofluorescence test, using anti-SA11 serum which would detect the simian, human, bovine, and porcine rotaviruses. No reaction was noted by immunofluorescence with the reoviruses or several common enteroviruses. The sewage isolates were neutralized by convalescent sera from a human adult and infant who had been infected by rotavirus as well as by a hyperimmune serum prepared in guinea pigs against purified human rotavirus. Preimmune or preillness sera did not react with the isolates by neutralization or immunofluorescence. The natural isolates were sensitive to pH 11 and other inactivating agents, similar to SA11. The buoyant density of the sewage isolates in CsCl gradients was 1.36 g/cm3, which is the value usually reported for complete, infectious rotavirus particles. The double-shelled particle diameter was 67.1 ± 2.4 nm. Finally, electron micrographs of cell lysates inoculated with the sewage isolate showed particles displaying characteristic rotavirus morphology.
• Gerba, C. P., & Keswick, B. H. (1981). Survival and transport of enteric viruses and bacteria in ground water. Studies in Environmental Science, 17(C), 511-515.
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  Abstract: Microbial contamination of groundwater is responsible for large outbreaks of waterborne disease. The most important pathogens that may enter groundwater are viruses and bacteria. Environmental factars affecting their survival and migration in groundwater have only recently come under study and have proven to be highly complex. Only by understanding these factors will it be possible to control or prevent microbial contarnination of groundwater. © Elsevier Scientific Publishing Company -Printed in The Netherlands.
• Gerba, C. P., Goyal, S. M., Cech, I., & Bogdan, G. F. (1981). Quantitative assessment of the adsorptive behavior of viruses to soils. Environmental Science and Technology, 15(8), 940-944.
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  Abstract: To evaluate the potential for groundwater contamination by viruses, it is essential to understand the processes controlling virus adsorption to soil. Recent laboratory studies have indicated that the degree of viral adsorption is highly type and strain dependent. The purpose of this study was to statistically reexamine earlier data by grouping studied variables into a number of broad categories. The results indicated that different types and strains of viruses can be grouped by their ability to be similarly affected by certain soil characteristics. For group I, the most important factors affecting adsorption were pH, organic matter, and exchangeable iron content of the soil. No studied soil characteristic was found to be significantly associated with adsorption of group II viruses. The implication is that adsorption-elution of group I viruses is more sensitive to certain soil characteristics than that of group II. Certain types of coliphages were found to be better models for some types of enteroviruses than others.
• Goyal, S. M., Keswick, B. H., & Gerba, C. P. (1981). OCCURRENCE OF VIRUSES IN GROUNDWATER AND SOIL BENEATH THREE LAND APPLICATION SITES.. Proceedings - Water Reuse Symposium, 3, 2251-2260.
• Hejkal, T. W., & Gerba, C. P. (1981). Uptake and survial of enteric viruses in the blue crab, Callinectes sapidus. Applied and Environmental Microbiology, 41(1), 207-211.
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  PMID: 6261683;PMCID: PMC243665;
• Keswick, B. H., & Gerba, C. P. (1981). FATE AND TRANSPORT OF VIRUSES DURING LAND TREATMENT OF SEWAGE. .. Proceedings - Water Reuse Symposium, 3, 2261-2281.
• Keswick, B. H., Gerba, C. P., & Goyal, S. M. (1981). Occurrence of enteroviruses in community swimming pools. American Journal of Public Health, 71(9), 1026-1030.
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  PMID: 6267950;PMCID: PMC1619862;Abstract: Municipal swimming pools and wading pools were examined for the presence of human enteric viruses using a portable virus concentrator at the site to concentrate viruses from 100-gallon to 500-gallon samples. Ten of 14 samples contained viruses; three of these were positive for virus in the presence of residual free chlorine. Enteroviruses were isolated from two pools which exceeded the 0.4 ppm free residual chlorine standard. This study appears to be supportive of recent evidence that indicates a higher incidence of enterovirus infection among bathers. All seven wading pool samples contained virus. Coxsackieviruses B3 and B4, poliovirus 1, and echovirus 7 were isolated. Total coliform bacteria were not adequate indicators of the presence of virus, as six of the samples were positive for virus but negative for coliforms. Total plate counts appeared to provide a better indication of the sanitary quality of the pool water, but viruses could still be detected in samples that met currently recommended bacterial levels. It is possible that swimming and wading pools may serve as a means of transmission of enteroviral disease, especially in children, during summer months.
• Wang, D., Gerba, C. P., & Lance, J. C. (1981). Effect of soil permeability on virus removal through soil columns. Applied and Environmental Microbiology, 42(1), 83-88.
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  PMID: 6266338;PMCID: PMC243967;Abstract: Laboratory experiments were performed on four different soils, using 100 cm long columns, to determine the extent of virus movement when wastewater percolated through the soils at various hydraulic flow rates. Unchlorinated secondary sewage effluent seeded with either poliovirus type 1 (strain LSc) or echovirus type 1 (isolate V239) was continuously applied to soil columns for 3 to 4 days at constant flow rates. Water samples were extracted daily from ceramic samples at various depths of the column for the virus assay. The effectiveness of virus removal from wastewater varied greatly among the different soil types but appeared to be largely related to hydraulic flow rates. At a flow rate of 33 cm/day. Anthony sandy loam removed 99% of seeded poliovirus within the first 7 cm of the column. At flow rates of 300 cm/day and above, Rubicon sand gave the poorest removal of viruses; less than 90% of the seeded viruses were removed by passage of effluent through the entire length of the soil column. By linear regression analyses, the rate of virus removal in soil columns was found to be negatively correlated with the flow rate of the percolating sewage effluent. There was no significant difference in rate of removal between poliovirus and echovirus in soil columns 87 cm long. The rate of virus removal in the upper 17 cm of the soil column was found to be significantly greater than in the lower depths of the soil column. This study suggests that the flow rate of water through the soil may be the most important factor in predicting the potential of virus movement into the groundwater. Furthermore, the length of the soil column is critical in obtaining useful data to predict virus movement into groundwater.
• Gerba, C. P., Goyal, S. M., Hurst, C. J., & Labelle, R. L. (1980). Type and strain dependence of enterovirus adsorption to activated sludge, soils and estuarine sediments. Water Research, 14(9), 1197-1198.
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  Abstract: The degree of enterovirus adsorption to surfaces was found to be both type- and strain-dependent. © 1980.
• Goyal, S. M., & Gerba, C. P. (1980). Simple method for concentration of bacteria from large volumes of tap water. Applied and Environmental Microbiology, 40(5), 912-916.
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  PMID: 7004354;PMCID: PMC291689;
• Goyal, S. M., Gerba, C. P., & Lance, J. C. (1980). Movement of endotoxin through soil columns. Applied and Environmental Microbiology, 39(3), 544-547.
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  PMID: 7387154;PMCID: PMC291375;
• Goyal, S. M., Hanssen, H., & Gerba, C. P. (1980). Simple method for the concentration of influenza virus from allantoic fluid on microporous filters. Applied and Environmental Microbiology, 39(3), 500-504.
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  PMID: 7387152;PMCID: PMC291367;Abstract: Membrane filter adsorption-elution is an efficient method for concentration and partial purification of several types of viruses from various aqueous solutions. For efficient virus adsorption to negatively charged filters, the sample is adjusted to pH 3.5 and trivalent salts are added before filtration. Since influenza virus is sensitive to extremes in pH, it cannot be concentrated by ordinary filters. Zeta Plus filters, which have a net positive charge of up to 5 or 6, were evaluated for the concentration of influenza virus from infectious allantoic fluids. Influenza virus efficiently adsorbed to Zeta Plus filters at pH 6, and addition of salts was not necessary. Adsorbed virus was eluted in a small volume of 2% bovine serum albumin plus 1 M NaCl at pH 10. By this procedure, viruses in 100 ml of allantoic fluid were concentrated to a final volume of 8 ml, with an average recovery efficiency of 71.0%.
• Goyal, S. M., Zerda, K. S., & Gerba, C. P. (1980). Concentration of bacteriophage lysates by filter chromatography. Journal of Virological Methods, 1(2), 79-85.
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  PMID: 7228970;Abstract: High-titered phage stocks are required for carrying out genetic and physicochemical studies on bacteriophages. This study describes a simple method for the concentration of coliphages MS-2 and T2 by charge-modified filters. Phage lysates were first clarified by filtration through serum-coated membrane filters. The clarified lysate was adjusted to pH 6 and passed through a Zeta-plus filter (30 S size). Greater than 99% virus adsorption occurred under these conditions. Adsorbed viruses were successfully eluted by small volumes of 3% beef extract (pH 10) which was subsequently neutralized with 3% beef extract (pH2). A concentration factor as great as 126 could be achieved by this method, with recoveries ranging from 54% to 97% (average = 69%). © 1980.
• Goyal, S. M., Zerda, K. S., & Gerba, C. P. (1980). Concentration of coliphages from large volumes of water and wastewater. Applied and Environmental Microbiology, 39(1), 85-91.
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  PMID: 7356323;PMCID: PMC291288;
• Hou, K., Gerba, C. P., Goyal, S. M., & Zerda, K. S. (1980). Capture of latex beads, bacteria, endotoxin, and viruses by charge-modified filters. Applied and Environmental Microbiology, 40(5), 892-896.
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  PMID: 7004352;PMCID: PMC291685;
• Hurst, C. J., & Gerba, C. P. (1980). Stability of simian rotavirus in fresh and estuarine water. Applied and Environmental Microbiology, 39(1), 1-5.
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  PMID: 6243899;PMCID: PMC291273;Abstract: The rates of inactivation of poliovirus 1, echovirus 7, coxsackievirus B3, and simian rotavirus SA11 were compared in polluted and nonpolluted fresh and estuarine water samples. The study was done in two parts, comparing virus survival in samples taken 1 year apart from the same sites. The survival studies were performed at 20°C and at the natural pH of the water samples. In the first part of the study, the time required for a 3-log10 reduction in the initial virus titers was 2 to 3 days in the estuarine water samples and varied from 3 to >14 days in the freshwater samples. In the second part of the study, no clear distinction was found between survival of viruses in freshwater samples and survival in estuarine water samples. The time required for a 3-log10 reduction in the initial virus titers in the second part of the study varied from 12 to >14 days. This indicates that there is a nonseasonal change in factors in the water which affect virus survival. In this study SA11 survival time (used as a model for human virus) was well within the range exhibited by the enteroviruses, indicating that it also is environmentally stable in natural waters.
• Hurst, C. J., Gerba, C. P., & Cech, I. (1980). Effects of environmental variables and soil characteristics on virus survival in soil. Applied and Environmental Microbiology, 40(6), 1067-1079.
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  PMID: 6257161;PMCID: PMC291723;Abstract: Because of the increasing emphasis placed upon land application as a means of wastewater disposal, it is important to evaluate the influences of different factors upon virus survival in soil. The objective of this study was to measure the effects of various environmental variables on virus persistence. Test samples of soil were placed in vials, and the soil was wetted with suspensions of virus in either distilled water, unchlorinated secondary sewage effluent, or mixtures of effluent and water. The viruses used were coxsackieviruses A9 and B3, echovirus 1, poliovirurs 1, rotavirus SA11, and bacteriophages T2 and MS2. The rate of virus inactivation was evaluated statistically with regard to conditions under which the vials were incubated and to the soil characteristics. The factors that were found to influence virus survival were temperature, soil moisture content, presence of aerobic micro-organisms, degree of virus adsorption to the soil, soil levels of resin-extractable phosphorus, exchangeable aluminum, and soil pH. Overall, temperature and virus adsorption to soil appeared to be the most important factors affecting virus survival.
• Hurst, C. J., Gerba, C. P., Lance, J. C., & Rice, R. C. (1980). Survival of enteroviruses in rapid-infiltration basins during the land application of wastewater. Applied and Environmental Microbiology, 40(2), 192-200.
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  PMID: 6258471;PMCID: PMC291552;Abstract: The downward migration through soil of seeded poliovirus type 1 and echovirus type 1 and of naturally occuring enteroviruses during infiltration of sewage effluent through rapid-infiltration basins was investigated. After 5 days of flooding, the amount of seeded poliovirus type 1 that had migrated 5 to 10 cm downward through the soil profile was found to be 11% of that remaining at the initial burial depth. The amount of echovirus type 1 determined to have moved an equal distance was at least 100-fold less. Migration of naturally occurring enteroviruses during infiltration of sewage effluent through soil could not be measured with accuracy because of the possibility of virus survival from previous applications of effluent. The rate of inactivation for seeded poliovirus 1 and echovirus 1 buried in the infiltration basins ranged between 0.04 and 0.15 log10 units per day during the time when the basins were flooded. Inactivation of these same seeded virus types and of indigenous enterovirus populations in the infiltration basins during the drying portion of the sewage application cycle ranged between 0.11 and 0.52 log10 units per day. The rate of virus inactivation was dependent upon the rate of soil moisture loss. These results indicate that drying cycles during the land application of wastewater enhance virus inactivation in the soil.
• Keswick, B. H., & Gerba, C. P. (1980). Viruses in groundwater. Environmental Science and Technology, 14(11), 1290-1297.
• LaBelle, I. L., & Gerba, C. P. (1980). Influence of estuarine sediment on virus survival under field conditions. Applied and Environmental Microbiology, 39(4), 749-755.
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  PMID: 6246838;PMCID: PMC291414;
• LaBelle, R. L., Gerba, C. P., Goyal, S. M., Melnick, J. L., Cech, I., & Bogdan, G. F. (1980). Relationships between environmental factors, bacterial indicators, and the occurrence of enteric viruses in estuarine sediments. Applied and Environmental Microbiology, 39(3), 588-596.
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  PMID: 6247974;PMCID: PMC291383;Abstract: Current standards for evaluation of the public health safety of recreational and shellfish-harvesting waters are based upon bacteriological analysis, but do not include an evaluation of the number of viruses. The objective of this study was to determine the occurrence of enteric viruses in estuarine sediments and to find a relationship, if any, between the presence of viruses in seawater or sediment or both and various biological and physicochemical characteristics of the environment. Viruses were found in greater numbers in sediment than in overlying seawater on a volume basis. Several types of enteroviruses were isolated: coxsackievirus types A16, B1, and B5, echovirus type 1, and poliovirus type 2. On several occasions, viruses were isolated from sediments when overlying seawaters met bacteriological water quality standards for recreational use. Statistical analysis of the relationship between viruses in seawater or in sediment and other variables measured yielded only one significant association: the number of viruses in sediment was found to be positively correlated with the number of fecal coliforms in sediment. No other physical, chemical, or biological characteristic of seawater or sediment that was measured showed statistically significant association with viral numbers. No correlation was found between bacterial indicators and virus in the overlying waters. The data indicated that evaluation of the presence of bacteria and viruses in sediment may provide additional insight into long-term water quality conditions and that indicator bacteria in water are not reflective of the concentration of enteric viruses in marine waters.
• Lance, J. C., & Gerba, C. P. (1980). Poliovirus movement during high rate land fitration of sewage water. Journal of Environmental Quality, 9(1), 31-34.
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  Abstract: Research with soil columns that are good models of a field ground water recharge system showed that most polioviruses are held near the soil surface. Secondary sewage effluent seeded with poliovirus type 1 (LSc) was filtered through 250-cm columns packed with calcareous sand from an area in the Salt River bed that is used for ground water recharging of secondary sewage effluent. When the concentration of poliovirus added to the sewage water was increased from 0.9x102 to 2.6x104 PFU/ml, the number of viruses detected at each soil depth increased with the increasing virus concentration in the sewage water. However, the percentage of added viruses that remained at each depth was about the same for each concentration. The differences in the strength of the negative charge among members of a given viral population could account for the adsorption of some viruses near the soil surface while others move farther through the profile. Increasing the flow rate from 0.6 to 1.2 m/day caused a virus breakthrough of
• Liew, P. F., & Gerba, C. P. (1980). Thermostabilization of enteroviruses by estuarine sediment.. Applied and Environmental Microbiology, 40(2), 305-308.
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  PMID: 6258475;PMCID: PMC291571;Abstract: The effect of estuarine sediment on the thermoinactivation of poliovirus type 1 and echovirus type 1 was evaluated. Poliovirus survival was prolonged at 24 and 37 degrees C but not at 4 degrees C in the presence of sediment over the time periods observed. Further inactivation studies were performed at 50 and 55 degrees C to maximize the thermal effects, and similar protection was observed. The supernatant fluid from a mixture of seawater and sediment lacked the protective effect against thermoinactivation, suggesting that prolonged virus survival in the presence of sediment was due to adsorption to particulates. From these observations, it appears that the adsorption of enteroviruses to estuarine sediments may play a significant role in protecting them against thermoinactivation.
• Marzouk, Y., Goyal, S. M., & Gerba, C. P. (1980). Relationship of viruses and indicator bacteria in water and wastewater of Israel. Water Research, 14(11), 1585-1590.
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  Abstract: Different aquatic resources of Israel were monitored to obtain information on the occurrence of enteroviruses and their relationship to the bacteriological indicators of water quality. A total of 155 samples of groundwater, potable water and swimming pool water were examined, of which 45 (29.0%) yielded virus. Echovirus type 7 was the most predominant, followed by poliovirus 1, echovirus 6 and coxsackieviruses B2, B5 and B6. Virus was isolated on several occasions when the water in question met current bacteriological standards. Viruses were isolated from water samples with no detectable fecal or total coliform bacteria. No significant statistical correlation could be determined between the occurrence of bacterial indicators and the presence of viruses. This study raises serious doubts about the validity of the indicator bacteria concept to predict the virological quality of water, particularly in countries with a high incidence of enteric viral disease.
• Melnick, J. L., & Gerba, C. P. (1980). Viruses in water and soil. Public Health Reviews, 9(3-4), 185-213.
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  PMID: 6287537;
• Melnick, J. L., Gerba, C. P., & Berg, G. (1980). The ecology of enteroviruses in natural waters. Critical Reviews in Environmental Control, 10(1), 65-70.
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  Abstract: More than 100 different enteric viruses are known to be excreted in human feces. More than 1 million viruses may be excreted per gram of feces, and concentrations as high as 500,000 infectious virus particles per liter have been detected in raw sewage. Certain enteric viruses can persist for long periods of time in the environment. Reported survival times range from 2 to 168 in tapwater, 2 to 130 days in seawater, 25 to 125 days in soil, and up to 90 days in oysters. There are many potential routes of transmission back to man. An evaluation of the problems associated with viruses in water was prepared recently by the World Health Organization Scientific Group on Human Viruses in Water, Wastewater, and Soil which met in Geneva in October, 1978. Among its conclusions, 4 are pertinent to this article: Viruses have been detected in the drinking water supply systems of a number of cities (including Paris and Moscow), despite the fact that those waters have received conventional water treatment considered adequate for protection against bacterial pathogens. Conventional bacterial pollution indicators used to evaluate the safety of potable water supply have been shown to be significantly less resistant than viruses to environmental factors and water and wastewater treatment processes. This leads to a situation where the more resistant enteric viruses can be present in water manifesting little or no signs of bacterial pollution. Regular virus monitoring should be carried out to assure the freedom from enteric viruses in 100- to 1000-l samples in large urban centers where the water supply is derived from virus-polluted surface water, a significant portion of which is untreated wastewater or effluent insufficiently treated to inactivate viruses. The constant exposure of large population groups to even relatively small numbers of enteric viruses in large volumes of water can lead to an endemic state of virus dissemination in the community which can and should be prevented.
• Wang, D. S., Lance, J. C., & Gerba, C. P. (1980). Evaluation of various soil water samplers for virological sampling. Applied and Environmental Microbiology, 39(3), 662-664.
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  PMID: 6247976;PMCID: PMC291394;Abstract: Two commercially available soil water samplers and a ceramic sampler constructed in our laboratories were evaluated for their ability to recover viruses from both tap water and secondary sewage effluent. The ceramic sampler consistently gave the best recoveries of viruses from water samples. Soil columns containing ceramic samplers at various depths provide a simple method for studying virus transport through sewage-contaminated soils.
• Estes, M. K., Graham, D. Y., Gerba, C. P., & Smith, E. M. (1979). Simian rotavirus SA11 replication in cell cultures. Journal of Virology, 31(3), 810-815.
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  PMID: 229253;PMCID: PMC353508;Abstract: Understanding the basic virology of rotavirus infections has been hampered by the fastidiousness of most isolates and by the lack of a rapid quantitative assay method. The growth characteristics of the simian rotavirus SA11 were studied because it grows to high titers in tissue culture and infectivity can be quantitated by plaque assay. SA11 replication was analyzed in a variety of primary cell cultures or continuous cell lines derived from both homologous and heterologous hosts. Viral replication was observed in each of the cell cultures examined. The individual cell cultures demonstrated marked variability in their susceptibility to rotavirus infection. The highest titers were obtained with MA104, BSC-1, CV-1, and BGM cells. Observable cytopathic effect was found to correlate with the percentage of infected cells in the culture. This study presents growth curves of the simian rotavirus in a variety of cell cultures.
• Estes, M. K., Graham, D. Y., Smith, E. M., & Gerba, C. P. (1979). Rotavirus stability and inactivation. Journal of General Virology, 43(2), 403-409.
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  PMID: 39115;Abstract: The stability of the infectivity of Simian rotavirus, SAII, has been analysed and compared to the stability of reovirus type I. SAII infectivity was stable to freeze-thawing, sonication, incubation at 25°C overnight or at 37°C for 1 h and to treatment with acid, ether, chloroform and Genetron. In contrast to reovirus, the infectivity of SAII was more rapidly inactivated by heating at 50°C. SAII infectivity was inactivated above pH 10.0 and by heating at 50°C in 2 M-MgCl2, but was stabilized by heating in 2 M-MgSO4; reovirus I infectivity was enhanced by heating in MgCl2. Both SAII and reovirus I were inactivated by freezing in MgCl2. These results show that rotaviruses and reoviruses can be distinguished by their patterns of inactivation by physical and chemical agents.
• Gerba, C. P., & Stagg, C. H. (1979). Protection of viruses during disinfection by absorption to particulate matter.. Journal of the Water Pollution Control Federation, 51(2), 414-416.
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  PMID: 480510;
• Gerba, C. P., Goyal, S. M., LaBelle, R. L., & Bodgan, G. F. (1979). Failure of indicator bacteria to reflect the occurrence of enteroviruses in marine waters. American Journal of Public Health, 69(11), 1116-1119.
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  PMID: 228561;PMCID: PMC1619291;Abstract: The results of several studies conducted along the upper Texas Gulf coast, where a substantial amount of quantitative virological data were collected, are compared to bacteriological indicators and other environmental factors on a statistical basis. Variables common to all these studies were analyzed by multivariate regression. Although multivariate analysis indicated that the number of viruses detected in water was related to rainfall, salinity, and total coliforms in the water, the amount of variation in the number of viruses accounted for by these factors was not large enough to make them good predictors. Enteroviruses were detected 43 per cent of the time in recreational waters considered acceptable as judged by coliform standards, and 44 per cent of the time when judged by fecal coliform standards. Enteroviruses were detected 35 per cent of the time in waters which met acceptable standards for shellfish-harvesting. Our failure to correlate the occurrence of enteroviruses in marine waters with indicator bacteria, and the frequent occurrence of enteroviruses in water which met current bacteriological standards, indicates that these standards do not reflect the occurrence of enteroviruses, and perhaps other human pathogenic viruses, in marine waters.
• Goyal, S. M., & Gerba, C. P. (1979). Comparative adsorption of human enteroviruses, simian rotavirus, and selected bacteriophages to soils. Applied and Environmental Microbiology, 38(2), 241-247.
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  PMID: 42350;PMCID: PMC243473;Abstract: Virus adsorption to soils is considered to be the most important factor in removing after land treatment of wastewater. Most of the studies on virus adsorption to soils have utilized poliovirus as the model system. In the present study, comparative adsorption of a number of different types and strains of human enteroviruses and bacteriophages to nine different soil types was studied. Under the experimental conditions of this study, greater than 90% of all viruses adsorbed to a sandy loam soil except echovirus types 1, 12, and 29 and a simian rotavirus (SA-11), which adsorbed to a considerably lower degree. A great deal of variability was observed between adsorption of different strains of echovirus type 1, indicating that viral adsorption to soils is highly strain dependent. Of the five phages studied, f2 and φX174 adsorbed the least. In addition to being dependent on type and strain of virus, adsorption was found to be influenced also by type of soil. Thus, soils having a saturated pH of less than 5 were generally good adsorbers. From these results, it appears that no one enterovirus or coliphage can be used as the sole model for determining the adsorptive behavior of viruses to soils and that no single soil can be used as the model for determining viral adsorptive capacity of all soil types.
• Goyal, S. M., Gerba, C. P., & Melnick, J. L. (1979). Human enteroviruses in oysters and their overlying waters. Applied and Environmental Microbiology, 37(3), 572-581.
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  PMID: 222210;PMCID: PMC243257;Abstract: The presence of enteroviruses in oysters and oyster-harvesting waters of the Texas Gulf coast was monitored over a period of 10 mth. Viruses were detected in water and oyster samples obtained from areas both open and closed to shellfish harvesting. Viruses were detected periodically in waters that met current bacteriological standards for shellfish harvesting. No significant statistical relationship was demonstrated between virus concentration in oysters and the bacteriological and physicochemical quality of water and shellfish. Viruses in water were, however, moderately correlated with total coliforms in water and oysters and with fecal coliforms in oysters. Total coliforms in water were related to total coliforms and fecal coliforms in oysters and to fecal coliforms in water. Fecal coliforms in sediment were related only to total coliforms in sediment. Among the physicochemical characteristics of water, turbidity was related statistically to the organic matter content of water and to fecal coliforms in water. There was a marked effect of rainfall on the bacteriological quality of water. Of a total of 44 water samples, 26 yielded virus in concentrations from 4 to 167 plaque-forming units per 100-gallon (ca. 378.5-liter) sample. Of a total of 40 pools of 10 to 12 oysters each, virus was found in 14 pools at a concentration of 6 to 224 plaque-forming units per 100 g of oyster meat. On 5 occasions, virus was found in oysters but not in the overlying water. Similarly, viruses were isolated from 17 water samples when no virus could be detected in oysters harvested from the same sites. This study indicates that current bacteriological standards for determining the safety of shellfish and shellfish-growing waters do not reflect the occurrence of enteroviruses.
• Goyal, S. M., Gerba, C. P., & Melnick, J. L. (1979). R⁺ bacteria in estuarine sediments. Marine Pollution Bulletin, 10(1), 25-27.
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  Abstract: Increased construction of coastal canal communities had led to a deterioration of the water quality in the canals. In addition to being used for recreational activities, the canals serve as a dumping place for domestic sewage from these communities. This study was conducted to determine the prevalence of transferable drug-resistant (R+) bacteria in six coastal canals. A significantly higher number of R+ bacteria (both pathogenic and nonpathogenic) occurred in the bottom sediments than in the overlaying water. These sediments can be resuspended following rain, dredging, storms, boating, and diving, thus releasing their bacterial populations into the overlaying water. © 1979.
• Goyal, S. M., Gerba, C. P., & Melnick, J. L. (1979). Transferable drug resistance in bacteria of coastal canal water and sediment. Water Research, 13(4), 349-356.
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  Abstract: This study was undertaken to determine the comparative incidence of drug-resistant coliforms and salmonellae in the water and bottom sediments of six coastal canal communities which are used heavily for recreational activities. Of a total of 423 coliforms, 300 fecal coliforms and 100 salmonella isolates examined, 74.9% coliforms, 61.3% fecal coliforms and 71.0% salmonellae were resistant to one or more of the 12 antibiotics tested. Multiple resistance occurred in 48.9% coliforms, 32.7% fecal coliforms and 68.0% salmonella strains. A total of 178 coliforms, 137 fecal coliforms and 51 salmonella isolates were tested for the presence of resistance transfer factors, and 53.9%, 53.3% and 56.9% isolates, respectively, were capable of transferring their resistance patterns to Escherichia coli and/or Salmonella choleraesuis recipient strains. A significantly higher number of drug-resistant bacteria carrying R-factors (R+) was found to occur in sediment than in surface water.
• Hurst, C. J., & Gerba, C. P. (1979). Development of a quantitative method for the detection of enteroviruses in soil. Applied and Environmental Microbiology, 37(3), 626-632.
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  PMID: 36845;PMCID: PMC243266;Abstract: A method is described for efficiently concentrating enteroviruses from soil. Viruses were eluted from soil by mechanical agitation in high pH glycine buffer containing ethylenediaminetetraacetic acid. The eluted viruses were concentrated on a floc that formed de novo upon adjustment of the soil eluate to 0.06 M aluminum chloride and pH 3.5. Viruses not pelleted with the floc were concentrated by adsorption to and elution from membrane filters. This method yielded an average efficiency of 66% recovery from loamy sand soil for four enteroviruses. Virus recovery from soil was consistently high, with samples ranging in size from 25 to 500 g. The method was used successfully to isolate naturally occurring viruses from soil beneath a wastewater land treatment site. Recovery of enteroviruses by this method from different types of soil was dependent on percentage of clay, surface area, and cation exchange capacity. Recovery was not dependent on soil saturation pH or on percentage of organic matter. This method should prove useful for studying enterovirus migration and survival during the land application of domestic sewage.
• LaBelle, R. L., & Gerba, C. P. (1979). Influence of pH, salinity, and organic matter on the adsorption of enteric viruses to estuarine sediment. Applied and Environmental Microbiology, 38(1), 93-101.
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  PMID: 39508;PMCID: PMC243441;Abstract: This study was designed to determine the degree of adsorption of enteric viruses to marine sediment and factors controlling this association. Adsorption and elution characteristics of several enteroviruses and one rotavirus to estuarine sediments were studied under varying conditions of pH, salinity, and presence of soluble organics. Greater than 99% of the added poliovirus type 1 (LSc), coxsackievirus type B3 (Nancy), echovirus type 7 (Wallace), and rotavirus (SA-11) adsorbed to sediment. Echovirus 1 (Farouk) and a recent isolate typed as coxsackievirus B4 adsorbed significantly less than poliovirus 1 under similar conditions of varying salinity and pH. The presence of soluble organic matter, in the form of secondary sewage effluent or humic acid, did not affect these patterns of adsorption. Only echovirus 1 (Farouk) desorbed when the pH or salinity was altered and then only to a small extent. Three recent isolates of echovirus 1 and echovirus 29 (strain JV-10) also demonstrated varying amounts of adsorption to sediment. These data indicate that enteric viruses can become readily associated with sediment in the estuarine environment and that this association may play a major role in their hydrotransportation and survival.
• Marzouk, Y., Goyal, S. M., & Gerba, C. P. (1979). Prevalence of enteroviruses in ground water of Israel.. Ground Water, 17(5), 487-491.
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  Abstract: In this study, 99 ground-water samples were examined for the presence of enteroviruses, total bacteria, fecal coliforms, and fecal streptococci by standard methods. No statistical correlation between presence of virus and bacteriological indicators could be determined. The widespread failure of current bacteriological standards to indicate the presence of potentially pathogenic enteroviruses in ground water is an area of concern that requires more study.-from Authors
• Melnick, J. L., & Gerba, C. P. (1979). Is the water safe to drink?. Journal of Infectious Diseases, 139(6), 736-738.
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  PMID: 448201;
• Smith, E. M., Estes, M. K., Graham, D. Y., & Gerba, C. P. (1979). A plaque assay for the simian rotavirus SAII. Journal of General Virology, 43(3), 513-519.
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  PMID: 225432;Abstract: A sensitive, quantitative and reproducible plaque assay for the measurement of the simian rotavirus SA(II) is described. Plaque formation required the presence of the facilitators pancreatin or trypsin and diethylaminoethyl-dextran in the agar overlay. SA(II) produced plaques in three continuous primate cell lines: MA-104, CV-1 and LLC-MK2. MA-104 cells were the most sensitive.
• Wallis, C., Melnick, J. L., & Gerba, C. P. (1979). Concentration of viruses from water by membrane chromatography.. Annual Review of Microbiology, 33, 413-437.
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  PMID: 40529;
• Edmond, T. D., Schaiberger, G. E., & Gerba, C. P. (1978). Detection of enteroviruses near deep marine sewage outfalls. Marine Pollution Bulletin, 9(9), 246-249.
• Farrah, S. R., Goyal, S. M., Gerba, C. P., Conklin, R. H., & Smith, E. M. (1978). Comparison between adsorption of poliovirus and rotavirus by aluminum hydroxide and activated sludge flocs. Applied and Environmental Microbiology, 35(2), 360-363.
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  PMID: 205173;PMCID: PMC242838;Abstract: Adsorption of poliovirus and rotavirus by aluminum hydroxide and activated sludge flocs was studied. Both aluminum hydroxide and activated sludge flocs adsorbed greater amounts of poliovirus than rotavirus. Aluminum hydroxide flocs reduced the titer of poliovirus in tap water by 3 log 10, but they only reduced the titer of a simian rotavirus (SA-11) in tap water by 1 log 10 or less and did not noticeably reduce the number of human rotavirus particles present in a dilute stool suspension. Activated sludge flocs reduced the titer of added poliovirus by 0.7 to 1.8 log 10 and reduced the titer of SA-11 by 0.5 log 10 or less. These studies indicate that a basic difference in the adsorptive behavior of enteroviruses and rotaviruses exists and that water and wastewater treatment processes that are highly effective in removal of enteroviruses may not be as effective in removing other viral groups such as rotaviruses.
• Farrah, S. R., Goyal, S. M., Gerba, C. P., Conklin, R. H., Wallis, C., Melnick, J. L., & DuPont, H. L. (1978). A simple method for concentration of enteroviruses and rotaviruses from cell culture harvests using membrane filters. Intervirology, 9(1), 56-59.
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  PMID: 202572;Abstract: Organic compounds in cell culture harvests known as membrane coating components (MCC) prevent virus adsorption to membrane filters. Blending cell culture harvests with fluorocarbon removed the MCC and permitted adsorption of virus in acidified harvests to epoxy fiberglass filters. Subsequent elution with pH buffer resulted in recovery of greater than 90% of the virus with concentrations of up to 100 fold.
• Farrah, S. R., Goyal, S. M., Gerba, C. P., Mahajan, V. K., Wallis, C., & Melnick, J. L. (1978). Concentration of humic acid from tapwater. Water Research, 12(5), 303-306.
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  Abstract: Membrane filter procedures previously used for concentration of virus from tapwater were modified to concentrate humic acid. These procedures were capable of recovering approximately 50% of added humic acid from tapwater. Thirty milligrams of naturally occurring humic acid was detected in 1000-1. samples of tapwater. © 1978.
• Farrah, S. R., Goyal, S. M., Gerba, C. P., Wallis, C., & Melnick, J. L. (1978). Concentration of poliovirus from tap water onto membrane filters with aluminum chloride at ambient pH levels.. Applied and Environmental Microbiology, 35(3), 624-626.
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  PMID: 25048;PMCID: PMC242890;Abstract: A method is described for the concentration of an enterovirus from large volumes of tap water by addition of small amounts of aluminum chloride to enhance virus removal by membrane filters. Tap water treated with 2 X 10(-5) M aluminum chloride showed a slight decrease in pH (less than 0.5), a slight increase in turbidity, and enhanced removal of poliovirus by membrane filters. Virus was quantitatively recovered by treating the filters with a basic buffer, and this eluate was reconcentrated to a small volume by adsorption to aluminum hydroxide flocs. Using these procedures, virus from 1,000 liters of water was reduced to a final eluate of 20 to 80 ml with a mean recovery of 70%.
• Gerba, C. P., & Lance, J. C. (1978). Poliovirus removal from primary and secondary sewage effluent by soil filtration. Applied and Environmental Microbiology, 36(2), 247-251.
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  PMID: 211936;PMCID: PMC291209;Abstract: Adsorption of poliovirus from primary sewage effluent was similar to that from secondary sewage effluent in both batch soil studies and experiments with soil columns 240 cm long. Virus desorption by distilled water was also similar in a soil column that had been flooded with either primary or secondary effluent seeded with virus. These results indicated that adsorption of poliovirus from primary effluent and virus movement through the soil were not affected by the higher organic content of primary sewage effluent.
• Gerba, C. P., Farrah, S. R., Goyal, S. M., Wallis, C., & Melnick, J. L. (1978). Concentration of enteroviruses from large volumes of tap water, treated sewage, and seawater.. Applied and Environmental Microbiology, 35(3), 540-548.
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  PMID: 205175;PMCID: PMC242876;Abstract: Methods are described for the efficient concentration of an enterovirus from large volumes of tap water, sewage, and seawater. Virus in acidified water (pH 3.5) in the presence of aluminum chloride was adsorbed to a 10-inch (ca. 25.4 cm) fiberglass depth cartridge and a 10-inch pleated epoxy-fiberglass filter in a series at flow rates of up to 37.8 liters (10 gallons) per min. Adsorbed viruses were eluted from the filters with glycine buffer (pH 10.5 to 11.5), and the eluate was reconcentrated by using a combination of aluminum flocculation followed by hydroextraction. With this procedure, poliovirus in large volumes of tap water, seawater, and sewage could be concentrated with an average efficiency of 52, 53, and 50%, respectively. It was demonstrated that this method is capable of detecting surface solid-associated viruses originating from sewage treatment plants. No difference in virus recovery between laboratory batch studies and a set-up with acid-salt injection was found. This unified scheme for the concentration of viruses has many advantages over previously described systems. These include: high operating flow rates, low weight and small size, effectiveness with a variety of waters with widely varying qualities, and filters with a high resistance to clogging.
• Gerba, C. P., Stagg, C. H., & Abadie, M. G. (1978). Characterization of sewage solid-associated viruses and behavior in natural waters. Water Research, 12(10), 805-812.
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  Abstract: The association of bacteriophages and animal viruses with solids has been demonstrated to have a protective effect, resulting in enhanced survival in natural waters and resistance to inactivation by chlorine. In this study, attempts were made to differentiate solid-associated viruses and freely suspended viruses in secondarily treated sewage by the retention of sewage solids on membrane filters treated with fetal calf serum to prevent adsorption of freely suspended virus. Solid-associated viruses collected on membrane filters were eluted with pH 11.5, 0.05 M glycine buffer. The percentage of the total coliphage and animal virus associated with solids in secondarily treated sewage discharges ranged from
• Goyal, S. M., Gerba, C. P., & Melnick, J. L. (1978). Prevalence of human enteric viruses in coastal canal communities. Journal of the Water Pollution Control Federation, 50(10), 2247-2256.
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  Abstract: Several residential canal systems into which wastewater that had received secondary treatment was being discharged were studied to assess the nature, extent, and sanitary significance of human enteric viruses in these waters and to determine the relationship, if any, between the presence of viruses, indicator bacteria, and other physicochemical characteristics of the water in these canals. Significant concentrations of enteric viruses were found in recreational coastal waters which met acceptable bacteriological standards for contact recreational activity. No significant statistical relationship was demonstrated between virus concentration and the presumptive total coliforms in sediments. No correlation was found between virus number and various physicochemical characteristics of water. On several occasions pathogenic human enteric viruses were isolated from water which contained no detectable fecal coliforms, indicating that conventional bacteriological indicators may not be suitable indicators for determination of a viral disease hazard.
• Hurst, C. J., Farrah, S. R., Gerba, C. P., & Melnick, J. L. (1978). Development of quantitative methods for the detection of enteroviruses in sewage sludges during activation and following land disposal. Applied and Environmental Microbiology, 36(1), 81-89.
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  PMID: 29559;PMCID: PMC243038;Abstract: The development and evaluation of methods for the quantitative recovery of enteroviruses from sewage sludge are reported. Activated sewage sludge solids were collected by centrifugation, and elution of the solid-associated virus was accomplished by mechanical agitation in glycine buffer at pH 11.0. Eluted viruses were concentrated either onto an aluminum hydroxide floc or by association with a floc which formed de novo upon adjustment of the glycine eluate to pH 3.5. Viruses which remained in the liquid phase after lowering the pH of the glycine eluate were concentrated by adsorption to and elution from membrane filters. The method of choice included high pH glycine elution and subsequent low pH concentration; it yielded an efficiency of recovery from activated sludge of 80% for poliovirus type 1, 68% for echovirus type 7, and 75% for Coxsackie virus B3. This method was used to study the survival of naturally occurring virus in sludge at a sewage treatment plant and after subsequent land disposal of the solids after aerobic digestion. Reductions of enterovirus titers per gram (dry weight) of solids were modest during sludge activation but increased to a rate of 2 log10/wk after land disposal.
• Melnick, J. L., Gerba, C. P., & Wallis, C. (1978). Viruses in water. Bulletin of the World Health Organization, 56(4), 499-508.
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  PMID: 310357;PMCID: PMC2395640;Abstract: Attention is drawn in this paper to the increasing problem of viral contamination of water and shellfish, particularly since growing demands for available water resources by a rising world population and expanding industry will make the recycling of wastewater almost inevitable in the future. The problem of eliminating viruses pathogenic for man from water is considered in the light of present water treatment procedures, which are often inadequate for that purpose. Man may be exposed to waterborne viruses through the consumption of contaminated water, shellfish, or crops, as a result of recreational activities involving water, or from aerosols following the spraying of crops with liquid wastes. Physical and chemical methods of eliminating viruses from water are discussed.
• Smith, E. M., Gerba, C. P., & Melnick, J. L. (1978). Role of sediment in the persistence of enteroviruses in the estuarine environment. Applied and Environmental Microbiology, 35(4), 685-689.
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  PMID: 206204;PMCID: PMC242906;Abstract: The survival of four enteroviruses commonly found in sewage effluents was examined when the viruses were adsorbed to marine sediments in estuarine water and compared with virus survival in estuarine water alone. Echovirus 1, coxsackieviruses B3 and A9, and poliovirus 1 survived longer when associated with marine sediment. When the estuarine water was polluted with secondarily treated sewage effluent, virus survived for prolonged periods in sediments, but not in the overlaying estuarine water.
• Stagg, C. H., Wallis, C., Ward, C. H., & Gerba, C. P. (1978). Chlorination of solids-associated coliphages. Progress in Water Technology, 10(1-2), 381-387.
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  Abstract: The purpose of this study was to investigate the effect that association of coli-phages with suspended solids had on disinfection by chlorine. Changes in the numbers of both freely suspended and solids-associated coliphages were observed during passage of effluent through municipal chlorine contact chambers. Solids-associated coliphages were more resistant to chlorination than were freely suspended coliphages. Laboratory studies demonstrated that most of the solids-associated phages were adsorbed to the surface of sewage solids rather than embedded.
• Farrah, S. R., Gerba, C. P., Goyal, S. M., Wallis, C., & Melnick, J. L. (1977). Regeneration of pleated filters used to concentrate enteroviruses from large volumes of tap water. Applied and Environmental Microbiology, 33(2), 308-311.
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  PMID: 192145;PMCID: PMC170682;Abstract: Pleated cartridge filters are capable of concentrating enteroviruses from large volumes (well over 2,000 liters) of tap water. These epoxy-fiberglass filters can be regenerated if they are treated with 0.1 N NaOH or autoclaved to inactivate any contaminating virus. The regenerated filters regained their ability to concentrate viruses from water at high flow rates.
• Farrah, S. R., Goyal, S. M., Gerba, C. P., Wallis, C., & Melnick, J. L. (1977). Concentration of enteroviruses from estuarine water. Applied and Environmental Microbiology, 33(5), 1192-1196.
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  PMID: 18088;PMCID: PMC170847;Abstract: Plated cartridge filters readily adsorb viruses in estuarine water at low pH containing aluminum chloride. Adsorbed viruses are efficiently recovered by treating filters with glycine buffer at high pH. By using these procedures, it was possible to recover approximately 70% of the poliovirus added to 400 liters of estuarine water in 3 liters of filter eluate. Reconcentration of virus in the filter eluate in small volumes that are convenient for viral assays was more difficult. Reconcentration methods described previously for eluates from filters that process tap water or treated wastewater were inadequate when applied to eluates from filters used to process estuarine water containing large amounts of organic compounds. Two methods were found to permit efficient concentration of virus in filter eluates in small volumes. In both methods, virus in 3 liters of filter eluate was adsorbed to aluminum hydroxide flocs and then recovered in approximately 150 ml of buffered fetal calf serum. Additional reductions in volume were achieved by ultrafiltration or hydroextraction. By using these procedures 60 to 80% of the virus in 3 liters of filter eluate could be recovered in a final volume of 10 to 40 ml.
• Gerba, C. P., Goyal, S. M., Smith, E. M., & Melnick, J. L. (1977). Distribution of viral and bacterial pathogens in a coastal canal community. Marine Pollution Bulletin, 8(12), 279-282.
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  Abstract: Significant concentrations of human enteric viruses and bacteria were found to be present in the water and sediment of a coastal canal community into which secondarily treated sewage was being discharged.
• Gerba, C. P., Smith, E. M., & Melnick, J. L. (1977). Development of a quantitative method for detecting enteroviruses in estuarine sediments. Applied and Environmental Microbiology, 34(2), 158-163.
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  PMID: 20839;PMCID: PMC242615;Abstract: Several investigators have reported on the detection of enteric viruses in marine sediments, but none determined the efficiency of their methods and only limited volumes of sediment were sampled. The purpose of this investigation was to develop a quantitative method for detecting enteroviruses in marine sediments so that their relative proportion to viruses freely suspended in estuarine water could be more accurately determined. Poliovirus was found to adsorb readily to natural marine sediments collected along the Texas Gulf coast. A number of substances were evaluated for their ability to elute adsorbed viruses. A solution of 10% fetal calf serum adjusted to pH 10.5 and 0.05 M ethylenediaminetetraacetate (pH 11.0) were found to be the best eluents. Using ethylenediaminetetraacetate as an eluent, it was possible to elute virus from large volumes of sediment and reconcentrate the sediment eluate into an economically assayable volume (30 to 50 ml). Poliovirus could be recovered from the sediment with an overall efficiency of 50%. This method was found to be satisfactory for the recovery of naturally occurring animal viruses in estuarine sediments from the upper Texas Gulf coast.
• Gerba, C. P., Wallis, C., & Melnick, J. L. (1977). Application of photodynamic oxidation to the disinfection of tapwater, seawater, and sewage contaminated with poliovirus.. Photochemistry and Photobiology, 26(5), 499-504.
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  PMID: 201951;
• Gerba, C. P., Wallis, C., & Melnick, J. L. (1977). Disinfection of wastewater by photodynamic oxidation. Journal of the Water Pollution Control Federation, 49(4), 575-583.
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  PMID: 864840;Abstract: This study was conducted to determine the feasibility of photodynamic oxidation for the disinfection of wastewater. Optimal parameters for the photodynamic inactivation of coliforms and poliovirus in wastewater by methylene blue were determined. Temperature, pH, dye concentration and sensitization time were all found to affect the amount of coliforms and poliovirus that could be inactivated for a given light exposure. Coliforms were far more sensitive to the dye and photoinactivation than poliovirus, but large reductions of poliovirus were possible under the appropriate conditions. Wastewater organics were found not to interfere with the photodynamic inactivation of the microorganisms. Solar energy was a practical alternative to the use of an artificial light source for the photodynamic process. Photodynamic inactivation would be of greatest use in systems where very large reductions in pathogenic bacteria and viruses are required, such as water recycling systems.
• Goyal, S. M., Gerba, C. P., & Melnick, J. L. (1977). Occurrence and distribution of bacterial indicators and pathogens in canal communities along the Texas coast. Applied and Environmental Microbiology, 34(2), 139-149.
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  PMID: 20838;PMCID: PMC242612;Abstract: Increased construction of residential canal communities along the southern coastline of the United States has led to a concern about their impact on water quality. Pollution of such dead-end canals is potentially hazardous because of their heavy usage for recreational activities. Coliforms, fecal coliforms, and salmonellae in the surface water and bottom sediments of six selected residential coastal canals were monitored over a period of 17 months. No statistically significant relationship was observed between the organism concentrations and temperature, pH, turbidity, and suspended solids content of water. An inverse relationship between the concentration of indicator organism and salinity of water was found, however, to occur at a 99.9% level of significance. All of the microorganisms studied were found to be present in greater numbers in sediments than in the overlying water, often by a factor of several logs. Heavy rainfall resulted in large increases in the number of organisms in both water and sediment samples. Our results indicate that bottom sediments in the shallow canal systems can act as reservoirs of enteric bacteria, which may be resuspended in response to various environmental factors and recreational activities.
• Hobbs, M., Gerba, C. P., Wallis, C., Melnick, J. L., & Lennon, J. S. (1977). PHOTODYNAMIC INACTIVATION OF INFECTIOUS AGENTS. ASCE J Environ Eng Div, 103(3), 459-472.
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  Abstract: The photodynamic inactivation of poliovirus by use of the photoreactive dye methylene blue at pH 10 and monochromatic lights was investigated on a continuous flow basis. The photodynamic inactivation process was effective for virus inactivation in clarified wastewater and requires various unit operations that are inherent to both the tertiary treatment of secondary effluent for phosphorus and ammonia removal and for the physical-chemical treatment of sewage. The process can be used in existing physical-chemical waste treatment plants, secondary waste treatment plants where tertiary treatment for nutrient and improved carbon removals are of concern, and water treatment plants where the lime-softening process is used for water purification. Photodynamic inactivation rates for poliovirus using methylene blue at pH 10 were sensitive to heat during sensitization and subsequent irradiation.
• Sobsey, M. D., Gerba, C. P., Wallis, C., & Melnick, J. L. (1977). Concentration of enteroviruses from large volumes of turbid estuary water. Canadian Journal of Microbiology, 23(6), 770-778.
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  PMID: 17465;Abstract: A method is described for the efficient concentration of viruses from large volumes of highly turbid estuary water. Virus in acidified seawater in the presence of aluminium chloride is adsorbed to a 10-in. (about 25.4 cm) fibreglass depth cartridge and 2- and 0.65-μm epoxy-fibreglass filters in series. This filter series is capable of efficiently adsorbing enteroviruses from 50 U.S. gallons (about 190 l) of estuary water of varying salinity and turbidity. Adsorbed viruses were eluted from the filters with glycine buffer (pH 11.5) and the eluate reconcentrated by using a precipitate formed by the addition of ferric chloride. Viruses were eluted from this precipitate with fetal calf serum. Using this procedure, four different enteroviruses in 50 gallons (about 190 l) of estuary water were concentrated 9000-to 12000-fold with an overall efficiency of 41%.
• Farrah, S. R., Gerba, C. P., Wallis, C., & Melnick, J. L. (1976). Concentration of viruses from large volumes of tap water using pleated membrane filters. Applied and Environmental Microbiology, 31(2), 221-226.
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  PMID: 187115;PMCID: PMC169751;Abstract: A method is described for the efficient concentration of viruses from large volumes of tap water in relatively short time periods. Virus in acidified tap water in the presence of aluminium chloride is adsorbed to a 10 inch (ca. 25.4 cm) fiber glass depth cartridge and a 10 inch pleated epoxy fiberglass filter in series at flow rates of up to 37.8 liters/min (10 gallons/min). This filter series is capable of efficiently adsorbing virus from greater than 19,000 liters (5,000 gallons) of treated tap water. Adsorbed viruses are eluted from the filters with glycine buffer (pH 10.5) and the eluate is reconcentrated using an aluminium flocculation process. Viruses are eluted from the aluminium floc with glycine buffer (pH 11.5). Using this procedure viruses in 1,900 liters (500 gallons) of tap water can be concentrated 100,000 fold in 3 h with an average recovery of 40 to 50%.
• Farrah, S. R., Goyal, S. M., Gerba, C. P., Wallis, C., & Shaffer, P. T. (1976). Characteristics of humic acid and organic compounds concentrated from tapwater using the aquella virus concentrator. Water Research, 10(10), 897-901.
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  Abstract: Humic acid and other organic compounds present in eluates from filters used to process large volumes of treated tapwater using the Aquella virus concentrator were found to share certain properties. Both humic acid and the other organic compounds in the filter eluates adsorbed to membrane filters at low pH, were eluted from membrane filters at high pH, interfered with virus adsorption to membrane filters, formed flocs at low pH, and were removed by anion-exchange resins. © 1976.
• Gerba, C. P., & McLeod, J. S. (1976). Effects of sediments on the survival of Escherichia coli in marine waters. Applied and Environmental Microbiology, 32(1), 114-120.
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  PMID: 788634;PMCID: PMC170015;Abstract: Escherichia coli, a fecal coliform, was found to survive for longer periods of time in unsterile natural seawater when sediment material was present than in seawater alone, and at least on one occasion growth was observed to occur. This enteric bacterium was found to increase rapidly in number in autoclaved natural seawater and autoclaved sediment taken from areas receiving domestic wastes, even when the seawater had salinities as high as 34 g/kg. However, in autoclaved seawater, growth was always more gradual and never reached numbers as high as those observed when sediment was present. It was found that nutrients were easily eluted from the sediment after autoclaving or upon addition to artificial seawater, but little elution occurred during mixing of the sediments with unsterile natural seawater. The longer survival of E. coli in the sediment is attributed to the greater content of organic matter present in the sediment than the seawater. These laboratory results, in part, could explain why on a volume basis larger numbers of coliforms and fecal coliforms were found in estuarine sediments than the overlaying water at field sites.
• Gilbert, R. G., Gerba, C. P., Rice, R. C., Bouwer, H., Wallis, C., & Melnick, J. L. (1976). Virus and bacteria removal from wastewater by land treatment. Applied and Environmental Microbiology, 32(3), 333-338.
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  PMID: 825040;PMCID: PMC170066;Abstract: Secondary sewage effluent and renovated water from four wells at the Flushing Meadows Wastewater Renovation Project near Phoenix, Arizona, in operation since 1967, were assayed approximately every 2 months in 1974 for viruses and enteric bacteria during flooding periods. No viruses or Salmonella sp. were detected in any renovated well water sample, and the numbers of fecal coliforms, fecal streptococci, and total bacteria were decreased by about 99.9% in the renovated well waters after the wastewater was filtered through about 9 m of soil.
• Gilbert, R. G., Rice, R. C., Bouwer, H., Gerba, C. P., Wallis, C., & Melnick, J. L. (1976). Wastewater renovation and reuse: virus removal by soil filtration. Science, 192(4243), 1004-1005.
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  PMID: 1273580;Abstract: Secondary sewage effluent and renovated water from four wells at the Flushing Meadows Wastewater Renovation Project near Phoenix, Arizona, in operation since 1967, were assayed approximately every 2 months in 1974 for viruses during flooding periods. Viruses, regularly found in the secondary effluent, were not detected in any renovated water samples. Our results indicated that human viral pathogens do not move through soil into the groundwater, but are apparently absorbed and degraded by the soil and reduced in numbers by a factor of at least 104 (99.99 percent removal).
• Lance, J. C., Gerba, C. P., & Melnick, J. L. (1976). Virus movement in soil columns flooded with secondary sewage effluent. Applied and Environmental Microbiology, 32(4), 520-526.
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  PMID: 185960;PMCID: PMC170300;Abstract: Secondary sewage effluent containing about 3 x 104 plaque forming units of polio virus type 1 (LSc) per ml was passed through columns 250 cm in length packed with calcareous sand from an area in the Salt River bed used for ground water recharge of secondary sewage effluent. Viruses were not detected in 1 ml samples extracted from the columns below the 160 cm level. However, viruses were detected in 5 of 43 100 ml samples of the column drainage water. Most of the viruses were adsorbed in the top 5 cm of soil. Virus removal was not affected by the infiltration rate, which varied between 15 and 55 cm/day. Flooding a column continuously for 27 days with the sewage water virus mixture did not saturate the top few centimeters of soil with viruses and did not seem to affect virus movement. Flooding with deionized water caused virus desorption from the soil and increased their movement through the columns. Adding CaCl2 to the deionized water prevented most of the virus desorption. Adding a pulse of deionized water followed by sewage water started a virus front moving through the columns, but the viruses were readsorbed and none was detected in outflow samples. Drying the soil for 1 day between applying the virus and flooding with deionized water greatly reduced desorption, and drying for 5 days prevented desorption. Large reductions (99.99% or more) of virus would be expected after passage of secondary sewage effluent through 250 cm of the calcareous sand similar to that used in our laboratory columns unless heavy rains fell within 1 day after the application of sewage stopped. Such virus movement could be minimized by the proper management of flooding and drying cycles.
• Payment, P., Gerba, C. P., Wallis, C., & Melnick, J. L. (1976). Methods for concentrating viruses from large volumes of estuarine water on pleated membranes. Water Research, 10(10), 893-896.
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  Abstract: The efficiency of cartridge filters with pleated membranes was determined for the recovery of poliovirus from large volumes of seawater. Flow rates of about 6 gal min-1 were obtained when a combination of a 3 and a 0.45 μm pleated filter were incorporated into the Wallis Melnick virus concentrator. The filters adsorbed poliovirus when water was acidified at pH 3.5 and aluminium chloride added at a final concentration of 0.0015 M. The filters retained their capacity to absorb virus particles, even after 600 gal (2268 l.) of very turbid estuarine water had been filtered. Viruses were eluted from the pleated filters with pH 11.5 glycine buffer and reconcentrated by precipitation with ferric chloride or aluminum chloride. Virus from 100 gal samples was concentrated into a final eluate volume of 20 to 100 ml, with virus recovery of about 50% being achieved in the material that had been concentrated 20,000 to 100,000 times.
• Gerba, C. P., & Schaiberger, G. E. (1975). Aggregation as a factor in loss of viral titer in seawater. Water Research, 9(5-6), 567-571.
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  Abstract: The failure of a large percentage of previously monodispersed virus added to artificial seawater to pass through membrane filters which would exclude the passage of aggregates indicated that extensive aggregation was taking place in the artificial seawater. The loss of viral titer in artificial seawater was found to be directly related to salinity as was the extent of aggregation. Aggregation also appeared to be taking place in natural seawater, but was not as extensive. Viral clumps formed in both natural and artificial seawater could be disaggregated by an increase in the amount of organic matter or a decrease in salinity. Aggregation may play a role in the initial decline of viral titer in seawater, as well as to reduce the number of 'infectious foci' present in seawater.
• Gerba, C. P., & Schaiberger, G. E. (1975). Effect of particulates on virus survival in seawater. Journal of the Water Pollution Control Federation, 47(1), 93-103.
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  PMID: 1121053;Abstract: This investigation attempted to determine the role of particulate matter in the survival of E. coli B B bacteriophage T2 in seawater. Viral survival studies in natural seawater that had been passed through membrane filters of various porosities or differentially centrifuged indicated that there are at least two classes of particulates naturally present in seawater affecting loss of viral titer. One seemed to promote viral survival, while the other was antagonistic to survival. Kaolinite, a clay mineral, was shown to encourage the persistence of virus in seawater. The virus was shown to adsorb readily to kaolinite in seawater, with deadsorption occurring in the presence of organic matter and in solutions with low salt concentration.
• Gerba, C. P., Sobsey, M. D., Wallis, C., & Melnick, J. L. (1975). ADSORPTION OF POLIOVIRUS ONTO ACTIVATED CARBON IN WASTEWATER.. Environmental Science and Technology, 9(8), 727-731.
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  Abstract: The effect of pH and soluble organic matter on virus adsorption to activated carbon in treated sewage was determined. Poliovirus removal from wastewater effluent was greatly improved by lowering the pH to 3. 5-4. 5 or by reducing the amount of organics by lime coagulation. Batch studies indicated that virus adsorption to activated carbon in wastewater could be described by Freundlich isotherms. In column experiments virus removal was found to be dependent on column length as well as hydraulic loading. Virus and soluble organics adsorbed at low pH could become deadsorbed by a rise in pH.
• Gerba, C. P., Sobsey, M. D., Wallis, C., & Melnick, J. L. (1975). Enhancement of poliovirus adsorption in wastewater onto activated carbon. U.TEXAS WATER RESOUR.SYMP., No.7, 115-126.
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  Abstract: The use of physical chemical and other advanced waste treatment methods will probably predominate in future years. The activated carbon process is one of the methods offering the most promise, particularly since it has been found capable of adsorbing a great variety of organic materials including viruses. This investigation was undertaken to gain additional information on virus removal from sewage effluents by activated carbon and methods by which this process could be optimized. The results suggest that virus removal from waste water effluent by activated carbon is greatly improved by maintaining a pH = 3.5 to = 4.5 or by reducing the amount of waste water organics by lime coagulation. In these studies, activated carbon adsorption of organic pollutants from waste water at pH = 4.5 or below was comparable to that at pH = 8. Therefore, pH adjustments to below a pH = 4.5 could be applied to a final polishing column of activated carbon to ensure maximum virus removal as well as removal of other organic pollutants. Additional studies would be required to determine if carbon column operation under acidic conditions is both practical and economically feasible.
• Gerba, C. P., Wallis, C., & Melnick, J. L. (1975). Fate of wastewater bacteria and viruses in soil. J.IRRIGAT.DRAINAGE DIV.ASCE, 101(3 IR3), 157-174.
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  Abstract: Bacterial survival in soil is affected by moisture content, temperature, organic matter, and antagonism by soil microflora. In most instances the survival of bacterial pathogens in the soil is less than 2 to 3 mth. Removal of bacteria from sewage during percolation through the soil is accomplished largely at the soil surface by straining, sedimentation, and adsorption. While relatively large numbers of bacteria and viruses appear to be removed through a few feet of soil under normal conditions, once they have gained entrance into the underground aquifer distances of travel as far as several hundred feet have been observed. Removal of viruses by soil occurs largely by adsorption. Salt concentration, pH, soil composition, organic matter, and the electronegativity of the virus and the soil may influence the degree of retention of viruses by the soil. Viruses attached to soil particles can become deadsorbed with changes in water quality, resulting in greater subsurface travel. Viruses survive at least as long as pathogenic bacteria in the soil.
• Gerba, C. P., Wallis, C., & Melnick, J. L. (1975). Microbiological hazards of household toilets: droplet production and the fate of residual organisms. Journal of Applied Microbiology, 30(2), 229-237.
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  PMID: 169732;PMCID: PMC187159;Abstract: Large numbers of bacteria and viruses when seeded into household toilets were shown to remain in the bowl after flushing, and even continual flushing could not remove a persistent fraction. This was found to be due to the adsorption of the organisms to the porcelain surfaces of the bowl, with gradual elution occurring after each flush. Droplets produced by flushing toilets were found to harbor both bacteria and viruses which had been seeded. The detection of bacteria and viruses falling out onto surfaces in bathrooms after flushing indicated that they remain airborne long enough to settle on surfaces throughout the bathroom. Thus, there is a possibility that a person may acquire an infection from an aerosol produced by a toilet.
• Gerba, C. P., Wallis, C., & Melnick, J. L. (1975). VIRUSES IN WATER: THE PROBLEM, SOME SOLUTIONS.. Environmental Science and Technology, 9(13), 1122-1125.
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  Abstract: Increased demands on our available water resources because of the concurrent increase in world population and industrial demand make recycling of domestic wastewater inevitable in the future. This plus the provisions of the Federal Water Pollution Control Amendments of 1972 (P. L. 92-500), which require zero discharge of pollutants into the nation's water by 1985, have placed an urgent need on the development of recycling methods. One of the major problems to be overcome is the development of adequate methods to ensure the elimination of human pathogenic viruses from reclaimed water. Compounding this problem is the concern that present water treatment procedures may not regularly be sufficient in preventing viruses from reaching community water supplies.

Proceedings Publications

• Esteves, R. R., Gerba, C. P., & Slack P,E., D. C. (2019, September). Application of Microbial Risk Assessment of Escherichia coli in Irrigation Water on a Lettuce Crop.. In V Congresso Nacional de Riego y Drenaje, COMEII 2019., 8p.
• Gerba, C. P., & Bright, K. R. (2014). 1161Use Specific Quaternary Ammonium Formulations for controlling the spread of Noroviruses in Institutions. In Open Forum Infectious Diseases, 1, S345-S345.

Presentations

• Gerba, C. P. (2019, spring). Microbiall water quality of irrigation canals used for produce production. UNC Water Microbiology Confernce 2019University of North Carolina.
• Gerba, C. P. (2019, spring). Transport of pathogens in the environment. International Confernce on Food Safety and Biotechnology. Los Mochis, Mexico: National Assoication for Food Safety and Biotechology of Mexico.
• Gerba, C. P. (2019, summer). Preventing norovirus transmission in schools. Council of State and Territotial Epidemiologists Annual Confernce. Raleigh North Carolina: Council of State and Territotial Epidemiologists.
• Gerba, C. P., Reynolds, K. A., Gerald, J. K., & Verhougstraete, M. (2019, June). Cost-Benefit of Point of Use Devices for Lead Reductions. American Water Works Association ACE 2019. Denver, CO: WQRF.
• Reynolds, K. A., Canales, R. A., Gerba, C. P., Sexton, J., Reynolds, K. A., Canales, R. A., Gerba, C. P., & Sexton, J. (2017, June). Understanding the Relationships among HAI, Healthcare Surfaces, and Environmental Interventions using QMRA. 44th Annual Educational Conference of the Association for Professionals in Infection Control. Portland, OR.
• Reynolds, K. A., Gerba, C. P., Sexton, J. D., Humphrey, K., & Leslie, R. (2017, June). Effects of Disinfection on the Spread of Virus in an Outpatient Clinic. Association for Professionals in Infection Control. Portland, OR.
• Gerba, C. P. (2016, October). Application of microbial risk assessment to quantify hygiene product intervention. 4th recent advances in microbial control. San Diego, CA: Society for industrial microbiology and biotechnology.
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• Gerba, C. P. (2016, October). Infection control from the home to the health care environment. Workshop on combating infection risks in the healthcare environment. Tacoma, WA: Trining Workshop on quantitative microbial risk assessment.
• Gerba, C. P. (2016, September). Rethinking the signficance of reovirus in water. 5th international confernce on food and environmental virology. Kusatu, Japan.
• Gerba, C. P. (2016, august). Cleaning green in a germ filled world. Virgina school plant managers assoication annual conference. Richmand, VA: Virgina school plant managers assoication.
• Gerba, C. P. (2016, feburary). Water reuse - from Antarctica to the moon. seminar for the IGERT WATER SENSE at UC Riverside. University of California, Riverside, CA: IGERT grant to the University of California from the national sceicne foundation.
• Gerba, C. P. (2016, june). Advances in the detecton of viruses in water. 12th annual meeting of the central scienftic research unit of Quintana Roo. Cancun, Mexico: central scienftic research unit of Quintana Roo.
• Gerba, C. P. (2016, june). Infection control in the classroom. Annual confernce of the national assoication of school nurses. Indianpolis, IN: national assoication of school nurses.
• Gerba, C. P. (2016, november). Advances in the detection of viruses in foods. 1st international confernce on food safety and environment. Culican, Mexico: National Assoication for Food Safety and the Environment.
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• Gerba, C. P. (2016, november). Beware of the fomites. Annual meeting of the Arizona Chapter of American Practioners in infection control. Phoenix: Arizona chapter of APIC.
• Gerba, C. P. (2015, February 27, 2015). What’s new in infection control?. Annual Meeting of the New Mexico Branch of Practitioners in Infection Control. Albuquerque, New Mexico: New Mexico Branch of Practitioners in Infection Control.
• Gerba, C. P. (2015, February 4, 2015). Intervention Strategies to reduce risk of infectious diseases. ACDEHSA Environmental Health Conference. Laughlin, NV: Arizona Department of environmental Health Services.
• Gerba, C. P. (2015, February 7, 2015). Communicable disease prevention and management in schools. Florida Association of School Nurses Annual Meeting. Orlando, FL: Florida Association of School Nurses.
• Gerba, C. P. (2015, July 1, 2015). Environmentally better products for the sports industry. Green Sports Alliance Summit.. Chicago, IL: Green Sports Alliance.
• Gerba, C. P. (2015, July 20, 2015). Hygiene in the 21st Century. Annual Meeting of the Association for Career Technical Education of Arizona. Tucson, AZ: Association for Career Technical Educators of Arizona.
• Gerba, C. P. (2015, July 30-31, 2015). The need for infection control in our schools. Green Clean Schools Summit. Seattle, WA: Kroger Assoicates.
• Gerba, C. P. (2015, June 12, 2015). Hygiene in the washroom. Cannon Hygiene Global Conference 2015. Dublin, Ireland: Cannon Hygiene.
• Gerba, C. P. (2015, June 27, 2015). Infection control in the home. Annual Meeting of the American Association of Practitiaoners in Infection Control. Nashville, TN: American Association of Practitiaoners in Infection Control.
• Gerba, C. P. (2015, June 3, 2015). Hygiene in public places. Seminar to Maricopa County Public Health Department. Phoenix, AZ: Maricopa County Public Health Department.
• Gerba, C. P. (2015, March 11, 2015). A new self-disinfecting surface. Committee on Cruise Ship Industry Hygiene. Geneva, Switzerland: Cruise Ship Industry.
• Gerba, C. P. (2015, March 17, 2015). What’s new in infection control?. Meeting of the Southern California Branch of Practitioners in Infection Control. San Diego, CA: Southern California Branch of Practitioners in Infection Control.
• Gerba, C. P. (2015, May 4, 2015). The importance of fomites in the spread of infectious microorganisms. Annual Meeting of the Quebec Society of Infection Control. Victoriaville, Canada: The Quebec Society of Infection Control.
• Gerba, C. P. (2015, September 19, 2015). The impact on an enhanced hygiene protocol on the reduction of antibiotic use in child care centers. Interscience Conference on Antibiotics and Chemotherapy. San Diego, CA: Kroger Assoicates.
• Gerba, C. P. (2015, September, 20-23, 2015.). Effectiveness of UV light and hydrogen peroxide wipes on terminal cleaning. Annual Meeting Association of the Health Environment. Grapeville, TX: Clorox Company.
• Gerba, C. P. (2015, Winter). Infection Control in the 21st Century. Animal and Biomedical Sceinces Departmental Seminar. Tucson, AZ: Department of Animal and Biomedical Sceinces.
• Gerba, C. P. (2015, fall). Infection control in facilites. Annual Meeting of the International Sanitary Supply Assoication. Las Vegas, NV: International Sanitary Supply Assoication.
• Gerba, C. P. (2015, fall). Whats new in infection control. Annual meeting of practioners in infection control Northwest Branch. Core'lane Idaho: Northwest Branch of practioners in infection control.
• Gerba, C. P. (2015, winter). Hygiene advicefor new parents. Excellence in Pediatrics 2015. London, UK: Excellence in Pediatrics.
• Gerba, C. P., Pepper, I. L., & Schmitz, B. (2015, Fall). Bacteriophages as indicators of microbial water quality. Annual Meeting of the Water Environment Federation. Chicago, IL: Watet Environment Federation.
• Suppes, L. M., Reynolds, K. A., Ernst, K. C., & Gerba, C. P. (2013, January). Influence of Swimmer Activity and Behavior on Pool Water Ingestion. Arizona County Directors of Environmental Health Services Association. Laughlin, NV.
• Gerba, C. P. (2012). Childhood exposure factors to consider in risk assessment. Annual Conference of Water and Health. Chapel Hill, NC.
• Gerba, C. P. (2012). Deveopment of a new self-sanitizing surface. Symposium on Hospital Acquired Infections. Matsomoto, Japan.
• Gerba, C. P. (2012). Environmental virology: Past, Present and Future. 3rd International Congress of Food and Environmental Virology. Lisbon, Portgual.
• Gerba, C. P. (2012). Final barrier: global perspective. Annual Meeting of the Water Quality Association. Las Vegas, NV: Water Quality Association.
• Gerba, C. P. (2012). Germ Warfare in the 21st century: who is winning?. Academy Village. Tucson, AZ.
• Gerba, C. P. (2012). Infection control in indoor environments. Region 8 Forum of the National Association of Women in Construction. Tucson, AZ: National Association of Women in Construction.
• Gerba, C. P. (2012). Infection control in the 21st century. Annual Meeting of the Nevada Environmental Health Association. Las Vegas, NV: Nevada Environmental Health Association.
• Gerba, C. P. (2012). Infection control in the 21st century. Washington Dental Association Annual Meeting. Seattle, WA: Washington Dental Association.
• Gerba, C. P. (2012). Methods for the concentration of poliovirus from water. Center for Disease Control/Gates Fundation Workshop on Poliovirus Eradication. Atlanta, GA: Center for Disease Control/Gates Fundation.
• Gerba, C. P. (2012). Persistence and inactivation of biothreat agents and emerging pathogens. ASM Biodefense and Emerging Diseases Annual Conference. Washington, DC.
• Gerba, C. P. (2012). Surrogates for assesing UV light performance. Annual Meeting of the Ultraviolet Light Association. Washington, DC: Ultraviolet Light Association.
• Gerba, C. P. (2012). The economics of water sustainability-barriers, unrealized gains, and synergies. Annual Meeting of the International Life Science Institute. Phoenix, AZ: International Life Science Institute.
• Gerba, C. P. (2012). The final barrier in drinking water treatment. Annual Meeting of the Bottleless Water Association. Orlando, FL: Bottleless Water Association.
• Gerba, C. P. (2012). Virus survival and transport in groundwater. Department of Environmental Engineering, Colorado School of Mines. Golden, CO.
• Gerba, C. P. (2012). Waterborne diseases. Drinking Water Workshop. Phoenix, AZ: Arizona Department of Environmental Quality.
• Gerba, C. P. (2012, March). Biofilms and hospital acquired infections. Tucson, AZ: St. Mary's Hospital.
• Gerba, C. P. (2011). A low-cost family water treatment device. Calidad de Agua para todas las Comunidades. Mexico City, Mexico.
• Gerba, C. P. (2011). Assessment of water treatment devices. Household Water Treatment Workshop. Khartoum, Sudan.
• Gerba, C. P. (2011). Environmental monitoring for foodborne pathogens. Annual Meeting of the International Association for Food Protection. Milwaukee, WI: International Association for Food Protection.
• Gerba, C. P. (2011). How to keep Salmonella out of your salad. 18th Annual High Desert Gardening and Landscaping Conference. Sierra Vista, AZ.
• Gerba, C. P. (2011). Hygiene in the 21 st Century. Annual Conference of the Indiana Practitioners of Infection Control. Indianapolis, IN: Indiana Practitioners of Infection Control.
• Gerba, C. P. (2011). Hygiene in the 21st century. Annual Meeting of the Minnesota Dental Association. St. Paul, MN: Minnesota Dental Association.
• Gerba, C. P. (2011). Infection prevenrtion and control in healthcare settings: a global prespective. Petaling Jaya, Mayaysia: Malaysian Society of Infectious Diseases and Chemotherapy.
• Gerba, C. P. (2011). Microbial contamination of buses. American Public Transporation Association Annual Meeting. New Orleans: American Public Transporation Association.
• Gerba, C. P. (2011). Norovirus, the number one casue of foodborne outbreaks. Southwest Environmental Health Conference. Laughlin, NV.
• Gerba, C. P. (2011). Noroviruses. Annual Meeting of the Arizona Environmental Health Association. Phoenix, AZ: Arizona Environmental Health Association.
• Gerba, C. P. (2011). Reinventing hygiene in the 21st century. Maricopa County Environmental Health Services. Tucson, AZ.
• Gerba, C. P. (2011). Where the germs are and how to get rid of them. Workshop on Healthy Learning Environment. Holmdel, NJ.

Poster Presentations

• Gerba, C. P. (2019, fall). Evaluation of viruses common to wastewater as indicators of revese osmosis membrane system performance for portable reuse applications. 20th International Health Related Water Microbiology Symposium. Vienna, Austria: International Water Assoication.
• Wilson, A. M., Canales, R. A., Gerba, C. P., & Reynolds, K. A. (2018, April). How Much Are Surfaces to Blame in Norovirus Outbreaks?. Mel & Enid Zuckerman College of Public Health Research Forum. Tucson, AZ: Mel & Enid Zuckerman College of Public Health.
• Rock, C. M., & Gerba, C. P. (2014, 08/2014). The Assessment of Escherichia coli as an Indicator of Microbial Quality of Irrigation Waters Used for Produce. IAFP 2014. Indianapolis, IN.

Reviews

• Ijaz, M. K., Sattar, S. A., Nims, R. W., Boone, S. A., McKinney, J., & Gerba, C. P. (2023. Environmental dissemination of respiratory viruses: dynamic interdependencies of respiratory droplets, aerosols, aerial particulates, environmental surfaces, and contribution of viral re-aerosolization(pp e16420).
  More info

  During the recent pandemic of COVID-19 (SARS-CoV-2), influential public health agencies such as the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) have favored the view that SARS CoV-2 spreads predominantly droplets. Many experts in aerobiology have openly opposed that stance, forcing a vigorous debate on the topic. In this review, we discuss the various proposed modes of viral transmission, stressing the interdependencies between droplet, aerosol, and fomite spread. Relative humidity and temperature prevailing determine the rates at which respiratory aerosols and droplets emitted from an expiratory event (sneezing, coughing, .) evaporate to form smaller droplets or aerosols, or experience hygroscopic growth. Gravitational settling of droplets may result in contamination of environmental surfaces (fomites). Depending upon human, animal and mechanical activities in the occupied space indoors, viruses deposited on environmental surfaces may be re-aerosolized (re-suspended) to contribute to aerosols, and can be conveyed on aerial particulate matter such as dust and allergens. The transmission of respiratory viruses may then best be viewed as resulting from dynamic virus spread from infected individuals to susceptible individuals by various physical states of active respiratory emissions, instead of the current paradigm that emphasizes separate dissemination by respiratory droplets, aerosols or by contaminated fomites. To achieve the optimum outcome in terms of risk mitigation and infection prevention and control (IPAC) during seasonal infection peaks, outbreaks, and pandemics, this holistic view emphasizes the importance of dealing with all interdependent transmission modalities, rather than focusing on one modality.
• Silva-Beltrán, N. P., Boon, S. A., Ijaz, M. K., McKinney, J., & Gerba, C. P. (2023. Antifungal activity and mechanism of action of natural product derivates as potential environmental disinfectants.
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  There have been a considerable number of antifungal studies that evaluated natural products (NPs), such as medicinal plants and their secondary metabolites, (phenolic compounds, alkaloids), essential oils, and propolis extracts. These studies have investigated natural antifungal substances for use as food preservatives, medicinal agents, or in agriculture as green pesticides because they represent an option of safe, low-impact, and environmentally friendly antifungal compounds; however, few have studied these NPs as an alternative to disinfection/sanitation for indoor air or environmental surfaces. This review summarizes recent studies on NPs as potential fungal disinfectants in different environments and provides information on the mechanisms of inactivation of these products by fungi. The explored mechanisms show that these NPs can interfere with ATP synthesis and Ca++ and K+ ion flow, mainly damaging the cell membrane and cell wall of fungi, respectively. Another mechanism is the reactive oxygen species effect that damages mitochondria and membranes. Inhibition of the overexpression of the efflux pump is another mechanism that involves damage to fungal proteins. Many NPs appear to have potential as indoor environmental disinfectants.
• Gerba, C. P., Betancourt, W. Q., & Kitajima, M. (2017. How much reduction of virus is needed for recycled water: A continuous changing need for assessment?(pp 25-31).
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  To ensure the safety of wastewater reuse for irrigation of food crops and drinking water pathogenic viruses must be reduced to levels that pose no significant risk. To achieve this goal minimum reduction of viruses by treatment trains have been suggested. For use of edible crops a 6-log reduction and for production of potable drinking water a 12-log reduction has been suggested. These reductions were based on assuming infective virus concentrations of 10(5) to 10(6) per liter. Recent application of molecular methods suggests that some pathogenic viruses may be occurring in concentrations of 10(7) to 10(9) per liter. Factors influencing these levels include the development of molecular methods for virus detection, emergence of newly recognized viruses, decrease in per capita water use due to conservation measures, and outbreaks. Since neither cell culture nor molecular methods can assess all the potentially infectious virus in wastewater conservative estimates should be used to assess the virus load in untreated wastewater. This review indicates that an additional 2- to 3-log reduction of viruses above current recommendations may be needed to ensure the safety of recycled water. Information is needed on peak loading of viruses. In addition, more virus groups need to be quantified using better methods of virus quantification, including more accurate methods for measuring viral infectivity in order to better quantify risks from viruses in recycled water.
• Gerba, C. P. (2015. Quaternary Ammonium Biocides: Efficacy in Application(pp 464-469).

Other Teaching Materials

• Rock, C. M., Carr, D., Gerba, C. P., Bright, K., & Tamimi, A. (2015. AgWater App. University of Arizona.

Others

• Verhougstraete, M., Gerba, C. P., & Reynolds, K. A. (2016, September). Cost benefit of point-of-use devices in reduction of health risks from drinking water..
  More info

  Verhougstraete, M.P., K., Reynolds, A. Tamimi, and C. Gerba. 2016. Cost benefit of point-of-use devices in reduction of health risks from drinking water. A technical report For Water Quality Research Foundation.
• Elmaksoud, S. A., Patel, N., Maxwell, S. L., Sifuentes, L. Y., & Gerba, C. P. (2014, May). Use of household bleach for emergency disinfection of drinking water. Journal of environmental health.
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  Household bleach is typically used as a disinfectant for water in times of emergencies and by those engaging in recreational activities such as camping or rafting. The Centers for Disease Control and Prevention recommend a concentration of free chlorine of 1 mg/L for 30 minutes, or about 0.75 mL (1/8 teaspoon) of household bleach per gallon of water. The goal of the study described in this article was to assess two household bleach products to kill waterborne bacteria and viruses using the test procedures in the U.S. Environmental Protection Agency's Guide Standard and Protocol for Testing Microbiological Purifiers. Bleach was found to meet these requirements in waters of low turbidity and organic matter. While the test bacterium was reduced by six logs in high turbid and organic-laden waters, the test viruses were reduced only by one-half to one log. In such waters greater chlorine doses or contact times are needed to achieve greater reduction of viruses.
• Artiola, J. F., Artiola, J. F., Hix, G., Hix, G., Gerba, C. P., Gerba, C. P., Farrell-Poe, K. L., & Farrell-Poe, K. L. (2013, September). What Well Owners Should Know about Shock Chlorination. UA CALS Cooperative Extension, AZ1605. http://cals.arizona.edu/pubs/water/az1605.pdf
• Artiola, J., Hix, G., Gerba, C. P., & Farrell-Poe, K. (2013, June). What well owners should know abut shock colorination. extension bulltien.
  More info

  Extension Bulletin for homeowners who have private wells