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Rethinking Indicators of Microbial Drinking Water Quality for Health Studies in Tropical Developing Countries: Case Study in Northern Coastal Ecuador

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  • Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia; Department of Civil and Environmental Engineering, University of California, Berkeley, California; Division of Biostatistics, School of Public Health, Berkeley, California; Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, Michigan

To address the problem of the health impacts of unsafe drinking water, methods are needed to assess microbiologic contamination in water. However, indicators of water quality have provided mixed results. We evaluate five assays (three for Escherichia coli and one each for enterococci and somatic coliphage) of microbial contamination in villages in rural Ecuador that rely mostly on untreated drinking water. Only membrane filtration for E. coli using mI agar detected a significant association with household diarrheal disease outcome (odds ratio = 1.29, 95% confidence interval = 1.02–1.65 in household containers and odds ratio = 1.18, 95% confidence interval = 1.02–1.37) in source samples. Our analysis and other published research points to the need for further consideration of study design factors, such as sample size and variability in measurements, when using indicator organisms, especially when relating water quality exposure to health outcomes. Although indicator organisms are used extensively in health studies, we argue that their use requires a full understanding of their purposes and limitations.

Author Notes

*Address correspondence to Karen Levy, Department of Environmental Health, Emory University Rollins School of Public Health, 1518 Clifton Road NE, Atlanta, GA 30322. E-mail: karen.levy@emory.edu

Financial support: This study was supported by grants from the National Institute of Allergy and Infectious Diseases (RO1AI050038), the University of California Pacific Rim Research Program, and the University of California Center for Occupational and Environmental Health.

Authors’ addresses: Karen Levy, Department of Environmental Health, Emory University Rollins School of Public Health, Atlanta, GA, E-mail: karen.levy@emory.edu. Kara L. Nelson, Department of Civil and Environmental Engineering, University of California, Berkeley, CA, E-mail: nelson@ce.berkeley.edu. Alan Hubbard, Division of Biostatistics, University of California Berkeley School of Public Health, Berkeley, CA, E-mail: hubbard@stat.berkeley.edu. Joseph N. S. Eisenberg, Department of Epidemiology, University of Michigan School of Public Health, Ann Arbor, MI, E-mail: jnse@umich.edu.

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