Wade TJ, Krueger WS, Sams EA, Converse RR, Hudgens E, Dufour A. Health risks associated with swimming at an inland river. Presented at the Society for Epidemiological Research 48th Annual Meeting; June 16, 2015. Denver, CO.


Swimming exposure to fecally-contaminated oceans and lakes has been associated with an increased risk of gastrointestinal (GI) illness. Although treated and untreated sewage are often discharged to rivers, the health risks of swimming exposure on rivers has been less frequently studied. In the summer of 2011, we conducted a study on the Mississippi River near Davenport, Iowa to evaluate the risk of gastrointestinal (GI) illness among swimmers. The study site was a beach on the river, downstream from the discharge of several sewage treatment plants. We offered enrollment to those attending the beach on summer weekends. Participants completed a beach interview as they were leaving to determine swimming exposures. Ten to twelve days later, they completed a telephone interview to ascertain the occurrence of any new GI symptoms since the beach visit. Water samples were collected once each study day (n=11) and measured for indicators of fecal contamination. Logistic regression models were used to evaluate the association between GI symptoms and swimming exposures. Following exclusions for baseline illness, a total of 332 subjects had sufficiently complete follow up information to include in analysis. Fecal indicator bacteria at the river were well in exceedance of EPA’s recommended geometric mean (GM) criterion for Enterococcus with a GM of 384 colony forming units (CFU) per 100 ml (EPA recommended GM criterion=35 CFU per 100 ml), indicating the presence of high levels of fecal contamination. A higher percentage of swimmers who swallowed water reported diarrhea (15%) compared to other swimmers who did not swallow water (9%) and non-swimmers (5%). Adjusted odds ratios, controlling for age, were 2.17 (95% Confidence Interval= 0.90-5.21) and 4.64 (95% Confidence Interval=1.18-18.19) comparing swimmers who swallowed water with swimmers who did not swallow water and other non-swimmers, respectively. This abstract does not represent EPA policy.

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