Use of quantitative microbial risk assessment to improve interpretation of a recreational water epidemiological study

Abstract

We conducted a supplemental water quality monitoring study and quantitative microbial risk assessment (QMRA) to complement the United States environmental protection agency's (U.S. EPA) National Epidemiological and Environmental Assessment of Recreational water study at Boquerón beach in Puerto Rico to estimate the gastrointestinal (GI) illness levels associated with recreational water exposures. The previously reported epidemiological study had sufficient statistical power to detect an average illness rate of approximately 17 swimming associated GI illnesses per 1000 recreation events or greater, and found no consistent relationships between water quality measured by fecal indicator organisms (FIO) and swimming-associated illnesses (U.S. EPA, 2010a). The QMRA incorporated monitoring data for pathogens and fecal indicators collected during the epidemiological study period and calculated average swimming-associated illness levels that were approximately two GI illnesses per 1000 recreation events. To our knowledge, this is the first time that a comprehensive water quality monitoring program and QMRA analysis has been conducted in parallel with a recreational water epidemiological study. The QMRA results were consistent with the low rate of reported illnesses during the 2009 epidemiological study (i.e. <17 GI illnesses per 1000 recreation events) and provide additional context for understanding the epidemiological results. The results illustrate that coupling QMRA with an epidemiological study at a single study site provides a unique ability to understand human health illnesses especially under conditions where water quality, as measured by traditional FIO is good and/or average illness rates are lower than can be quantified via epidemiological methods alone.