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Human-associated fecal qPCR measurements and predicted risk of gastrointestinal illness in recreational waters contaminated with raw sewage
Citation:
Boehm, A., J. Soller, AND O. Shanks. Human-associated fecal qPCR measurements and predicted risk of gastrointestinal illness in recreational waters contaminated with raw sewage. Presented at 2016 Recreational Waters Conference, New Orleans, LA, April 12 - 15, 2016.
Impact/Purpose:
To inform the public.
Description:
We used quantitative microbial risk assessment (QMRA) to estimate the risk of gastrointestinal (GI) illness associated with swimming in recreational waters containing different concentrations of human-associated fecal qPCR markers from raw sewage– HF183 and HumM2. The volume/volume ratio of raw sewage to ambient water was determined by comparing the concentration in the recreational water to the concentrations in raw sewage from 54 different geographic locations across the United States. The concentrations of reference GI pathogens in raw sewage, volume ingested by swimmers, dose-response functions, and fraction of infected that become ill were adopted from previous studies. The QMRA model was implemented as a Monte Carlo simulation and did not consider immunity or person-to-person transmission of GI illness. Predicted GI risk increased with increased concentration of the human qPCR markers in ambient waters. The USEPA benchmark illness rate of 30 GI illnesses per 1000 swimmers occurred at predicted median concentrations of 4200 copies of HF183 and 2800 copies of HumM2 per 100 mL of recreational water. These results indicate that qPCR measurements made near the limit of quantification have the potential to be health-relevant. Future refinements of this model should consider risk as a function of human-associated qPCR marker concentrations from treated wastewater.