PREDICTING LIKELIHOOD OF GASTROENTERITIS FROM SEA BATHING - RESULTS FROM RANDOMIZED EXPOSURE

The health effects of bathing in coastal waters is an area of scientif ic controversy. We conducted the first ever randomised ''trial'' of an environmental exposure to measure the health effects of this activity . The trial was spread over four summers in four UK resorts and 1216 a dults took part. Detailed interviews were used to collect data on pote ntial confounding factors and intensive water quality monitoring was u sed to provide more precise indices of exposure. 548 people were rando mised to bathing, and the exposure included total immersion of the hea d. Crude rates of gastroenteritis were significantly higher in the exp osed group (14.8 per 100) than the unexposed group (9.7 per 100; p=0.0 1). Linear trend and multiple logistic regression techniques were used to establish relations between gastroenteritis and microbiological wa ter quality. Of a range of microbiological indicators assayed only fae cal streptococci concentration, measured at chest depth, showed a sign ificant dose-response relation with gastroenteritis. Adverse health ef fects were identified when faecal streptococci concentrations exceeded 32 per 100 mL. This relation was independent of non-water-related pre dictors of gastroenteritis. We do not suggest that faecal streptococci caused the excess of gastrointestinal symptoms in sea bathers but the se microorganisms do seem to be a better indicator of water quality th an the traditional coliform counts. Bathing water standards should be revised with these findings in mind.