RISK OF GASTROENTERITIS AMONG TRIATHLETES IN RELATION TO FECAL POLLUTION OF FRESH-WATERS

Background We conducted a prospective cohort study among endurance ath letes to investigate the effects of microbiological water quality on t he risk of gastroenteritis after bathing in fresh waters that meet cur rent water quality standards. We aimed to establish quantitative relat ionships, in order to evaluate current bathing water standards. Method s The study was spread over two summers, during which 827 triathletes (swimmers) in seven Olympic distance triathlons and 773 participants i n 15 run-bike-runs (non-swimming controls) participated. Intensive wat er quality monitoring was used to assess exposure to faecal indicator organisms and detailed questionnaires were used to collect data on the occurrence of health complaints and potential confounding factors. Re sults The microbiological water quality at the time of the triathlons met current Dutch and European bathing water standards. Dependent on t he case definition studied, gastroenteritis developed in 0.4-5.2% of s wimmers and 0.1-2.1% of non-swimmers in the week following exposure (o dds ratio [OR] = 1.6-2.3). Attack rates and burden of disease varied w ith the case definition used. Among swimmers, the attack rate of gastr oenteritis was significantly increased when the geometric mean concent ration of thermotolerant coliforms in the water at the time of exposur e was greater than or equal to 220/100 ml or the geometric mean concen tration of Escherichia coli was greater than or equal to 355/100 ml (O R comparing high versus low exposure 2.9-4.7 dependent on the case def inition studied). Thermotolerant coliform concentrations at these tria thlons ranged from 100/100 ml (the EU guide level) to 960/100 ml (the EU imperative level is 2000/100 ml). Below the threshold levels attack rates were comparable with attack rates among non-swimmers. A relatio n with other indicators of faecal pollution was not observed. Conclusi ons We observed that swimming in fresh waters that met the European im perative level for thermotolerant coliforms but failed the European gu ide level was associated with a significant risk of gastroenteritis am ong triathletes. This means that the current European imperative level for thermotolerant coliforms provides insufficient protection to gast rointestinal illness for those who are comparable with triathletes.