Development of Exposure-Response Relationships between Indicators of Water Quality and Swimming-Associated Illness
Timothy J. Wade1, Alfred P. Dufour2, Larry Wymer2
1National Health and Environmental Effects Reserach Laboratory, US EPA; 2National Exposure Research Laboratory, US EPA

Exposure to contaminated water quality during recreational swimming has long been associated with adverse health effects. Swimming in rivers, streams and lakes with high levels of fecal contamination are regularly linked to outbreaks of gastrointestinal illness and related infections. While these outbreaks may result in mild and self-limiting illnesses, more severe outbreaks of typhoid, shigellosis, hepatitis and viral gastroenteritis have also been reported. As early as the 1950s, epidemiology studies observed a higher occurrence of gastrointestinal symptoms among swimmers exposed to waters with higher fecal contamination as measured by coliform bacteria. Studies conducted during the 1970s by EPA and others led to the current recommended use of Enterococcus sp. and E. coli, common and normally harmless bacteria found in the intestinal tract of humans and other animals, as the preferred indicators of fecal contamination of recreational water quality. These indicator organisms are widely used to assess the microbial safety of recreational water. Since 2003, the US EPA has led a series of studies, enrolling over close to 50,000 respondents at beaches across the United States using novel and faster approaches to measure fecal indicator organisms. However, establishing “exposure-response” associations between indicators of water quality and swimming associated illness is far from straightforward. This presentation will review the basic assumptions behind these studies, discuss the concept of “acceptable risk” for recreational exposures, present the issues involved in interpreting results, and contrast different approaches to quantify exposure-response relationships. Data collected from the new series of EPA studies will used to illustrate the various approaches and models.

Keywords: Recreational Water; Diarrhea; Indicators; Exposure response models

Biography: Tim Wade is the Chief of the Epidemiology Branch at the United States Environmental Protection Agency in the National Health Effects Research Laboratory in Chapel Hill, North Carolina. Tim received his Ph.D in Epidemiology in 2001 from the University of California at Berkeley and a Master of Public Health Degree in Epidemiology and Biostatisitcs in 1998, also from UC Berkeley. His research focuses on describing and quantifying the health effects of exposure to waterborne contaminants.