Health effects of swimmers and nonpoint sources of contaminated water.

Microbiological contamination from nonpoint sources of pollution is usually related to animal faecal wastes through urban, pastureland and forest run-off of stormwater. Currently-used bacterial water quality indicators cannot discriminate between human and animal faecal contamination and, therefore, it is common practice to treat the risk associated with exposure to water polluted by animal or human wastes as equally hazardous. The purpose of this study was to determine if there is a risk of gastrointestinal illness after a swimming exposure to water contaminated with animal faecal wastes. The health status and swimming activity of volunteer study participants was followed for 49 days during June, July and August. Multiple bacterial indicators of water quality were monitored daily during the course of the study. Swimming-associated symptomatic gastrointestinal illness was observed in individuals who swam in animal nonpoint source contaminated water. Swimmer illness was not associated with high densities of common faecal indicator bacteria or high volume rainy days. Swimmer illness was associated with high numbers of swimmers per day and high densities of staphylococci. The observed illnesses appeared to be caused by a swimmer to swimmer transmission via the water.