Health effects of white-water canoeing.

There is little quantitative information on the relation between water quality and disease attack rates after recreational activities in fresh water. We conducted a prospective cohort study to measure the health effects of white-water and slalom canoeing in two channels with different degrees of microbial contamination. Site A, fed by a lowland river, showed high enterovirus concentrations (arithmetic mean 198 pfu per 10 litre and moderate faecal coliform concentrations (geometric mean 285/dl); at site B, from an upland impoundment, all samples were free of enteroviruses and the geometric mean faecal coliform concentration was 22/dl. Between 5 and 7 days after exposure canoeists using site A had significantly higher incidences of gastrointestinal and upper respiratory symptoms than canoeists using site B or non-exposed controls (spectators). Like seawater bathers, fresh-water canoeists can be made ill by sewage contamination. The hazard of fresh water may be best measured by counting of viruses rather than bacteria.