The health effects of swimming in ocean water contaminated by storm drain runoff

Waters adjacent to the County of Los Angeles (CA) receive untreated runoff from a series of storm drains year round. Many other coastal areas face a s imilar situation. To our knowledge, there has not been a large-scale epidem iologic study of persons who swim in marine waters subject to such runoff. We report here results of a cohort study conducted to investigate this issu e. Measures of exposure included distance from the storm drain, selected ba cterial indicators (total and fecal coliforms, enterococci, and Escherichia coli), and a direct measure of enteric viruses. We found higher risks of a broad range of symptoms, including both upper respiratory and gastrointest inal, for subjects swimming (a) closer to storm drains, (b) in water with h igh levels of single bacterial indicators and a low ratio of total to fecal coliforms, and (c) in water where enteric viruses were detected. The stren gth and consistency of the associations we observed across various measures of exposure imply that there may be an increased risk of adverse health ou tcomes associated with swimming in ocean water that is contaminated with un treated urban runoff.