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Exposure to human source fecal indicators and self-reported illness among bathers
Citation:
Napier, M., C. Poole, Rich Haugland, AND Tim Wade. Exposure to human source fecal indicators and self-reported illness among bathers. UNC Water Microbiology Conference, Chapel Hill, NC, May 18 - 22, 2015.
Impact/Purpose:
A preliminary evaluation of human specific markers as predictors of swimming related health effects
Description:
Introduction: Indicator microorganisms are used to predict the presence of fecal pollution in water and assess associated health risks, usually gastrointestinal illness and diarrhea. Few studies have characterized the health risks associated with human fecal sources using microbial indicators that can distinguish human fecal contamination in recreational waters. Our objective was to estimate the association between exposure to human source fecal indicator organisms and self-reported illness among bathers in the United States.Methods: We used data from 20,133 beach visitors enrolled in the National Epidemiological and Environmental Assessment of Recreational Water study in 2002-2009. Bathers were surveyed about beach activities, water exposure, and baseline symptoms on the day of their beach visit, and about health symptoms they experienced 10-12 days after the beach visit. Up to 18 water samples per day were collected and tested for human-specific Bacteroides spp. (HF183 TaqMan, BsteriF1, Bunif2, HumM2) using quantitative polymerase chain reaction (qPCR). We classified these human indicators in several binary categories according to the percentage of samples per day in which the indicator was detected: ≥50%, ≥80%, and ≥90%. Adjusted odds ratios (AOR) and 95% confidence intervals (CI) for the indicator-illness associations among bathers who immersed their bodies to the waist or higher were estimated using binomial regression. Robust standard errors were calculated due to clustering within beach and household. Results: We analyzed 3,271 water samples for human-associated Bacteroides spp. Human-associated Bacteroides spp. was detected in between 2 and 64% of samples per day, and varied by beach and assay used. In general, there appeared to be some evidence of a positive trend between the higher percentage of samples per day in which human indicators were detected and gastrointestinal and respiratory symptoms in the 10-12 days following their exposure. We found some evidence of increased association with diarrhea on days when ≥80% of samples indicated the presence of Bacteroides stericoris (AOR=1.28 (1.01, 1.62)) and with respiratory illness among bathers exposed to Bacteroides uniformis (AOR=1.28 (1.02, 1.60) or to any of the four assays (AOR=1.27(1.02,1.57)). However, we also observed several inverse associations with eye symptoms and rash, which are not as commonly associated with fecal contamination. Other indicator-illness associations were not associated with illness.Conclusion: In these preliminary analyses, we find some evidence that the risk self-reported illness is associated with exposure to recreational water contaminated with human fecal matter. HumM2 did not appear to be associated with any of the illnesses studied; gastrointestinal illness, ear infections and urinary tract infections did not appear to be associated with any of the human indicators studied. Future work will explore additional ways of classifying exposure and the joint effect of these human assays with conventional markers of fecal contamination.