Waterborne outbreak of gastroenteritis associated with a contaminated municipal water supply, Walkerton, Ontario, May-June 2000.

This report describes the findings of investigations led by the Bruce-Grey-Owen Sound Health Unit (BGOSHU) with the assistance of Health Canada and the Ontario Ministry of Health and Long-Term Care into an outbreak of gastroenteritis in Walkerton, Ontario, in May and June 2000. The purpose of these investigations was to determine the scope, the likely cause, and the contributing factors of the outbreak. This incident represents the first documented outbreak of Escherichia coli O157:H7 infection associated with a treated municipal water supply in Canada and the largest multi-bacterial waterborne outbreak in Canada to date.