Ground Beef Consumption in Noncommercial Settings Is a Risk Factor for Sporadic Escherichia coli O157:H7 Infection in Canada

The incidence of Escherichia coli O157:H7 infection in Canada continues to be high in areas where specimens of bloody and nonbloody diarrhea are routinely screened for this pathogen. Provincial laboratories reported 2432 cases of E. coli O157:H7 infection in 1989, a 29% increase over the 1885 cases reported in 1988 (Lior H, Laboratory Centre for Disease Control, personal communication). In 1989, the incidence in Calgary was 29/100,000; in Toronto, 4/100,000; and in Saskatoon, 18.5/100,000 (unpublished data). These rates generally are higher than the rate of 8/100,000 reported in the state of Washington in 1989. Previous outbreaks have most often incriminated ground beef, unpasteurized milk, and person-to-person spread as risk factors. However, studies of sporadic disease have been unable to identify a specific food item as a major risk factor. We conducted a case-control study during the summer months of 1990 to determine whether consumption of ground beef and specific summertime activities or food handling practices were risk factors for sporadic disease.