The Food Supply
Contaminated food is the major cause of E. coli outbreaks in North America.
Some mass outbreaks are caused by poor food-handling techniques at kitchens that serve many people, for example, at a restaurant, school, or hospital. Other mass outbreaks occur when a particular raw ingredient or prepared food becomes contaminated, and is then sold to many different consumers.
At Walkerton, the first reports of mass illness have come from several different institutions with separate kitchens - schools and a retirement home. The most probable situation, therefore, is that the source of the infection is not in one local kitchen, but that institutions have all bought and served the same contaminated food product.
As a precaution, since a small percentage of cases are carried through water, on May 19, the day the investigation begins, the public health unit contacts the manager of the municipal water system make sure that no unusual results have turned up during routine water testing. The unit is assured that the water has been "OK", which seems to confirm that investigators should be searching for a food item contaminated with E. coli.
