Environment/Climate Change
Swimmers are at higher risk of gastrointestinal illness when human-associated genetic markers of human fecal contamination are present Timothy Wade* Timothy Wade Elizabeth Sams Stephanie DeFlorio-Barker Alfred Dufour Richard Haugland Kevin Oshima Edward Hudgens Orin Shanks
Numerous epidemiological studies have found associations between the level of fecal contamination in recreational waters and the risk of gastrointestinal illness among swimmers. This association, however, is likely affected by the source of fecal contamination (e.g., human, avian, dog, etc.) and has been hypothesized to be strongest when humans are the primary source of the fecal contamination. We conducted an epidemiological study in 2015 at a Lake Michigan beach to evaluate the association between fecal contamination and swimming-associated gastrointestinal illness. A total of 533 beachgoers were enrolled and 10-14 days later completed a survey about symptoms experienced since the beach visit. Water samples were collected each study day and tested for both general indicators of fecal contamination (e.g., Enterococcus spp., E. coli, and coliphage) and human-associated Bacteroides genetic markers HumM2 and HF183/BacR287. One or both human markers were detected on 7 of the 13 study days. On days when human makers were detected associations between general fecal indicators and diarrhea among body-immersion swimmers were considerably stronger than days when human markers were absent. For example, among body-immersion swimmers, the odds ratios for diarrhea associated with a log increase in Enterococcus spp. CCE /100 ml and somatic coliphage PFU/L was 6.5 (95% CI 1.5-27.76) and 6.15 (95% CI 1.66-22.76), respectively. When human markers were absent these associations were not significant. Similar patterns were observed with the other general fecal indicators. These findings provide additional evidence that exposure to human-derived fecal contamination results in higher risks of swimming-associated illness.