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Risk factors for Escherichia coli O157:H7 infection in an urban community.

Outbreaks of Escherichia coli O157:H7 have been attributed to meat or meat products, particularly ground meat, and to unpasteurized dairy products. However, the risk factors for sporadic cases have not been clearly delineated. Study data were collected by using a self-administered dietary and historical questionnaire on all patients whose history included bloody diarrhea and who attended one of the participating emergency departments. Designation as "case" or "control" occurred after stool culture results were known, eliminating the possibility for recall bias common to this type of study. Cases (E. coli O157:H7-positive) were further matched with one diarrheal and one healthy community control, and more detailed information on food preparation practices and other data were then taken. Of 266 presentations of bloody diarrhea, 103 (38.7%) were due to E. coli O157:H7. Unmatched analyses with bloody diarrheal controls revealed a seemingly lower risk for E. coli O157:H7 infection in fast food restaurant patrons. No increased risk could be detected for ground meat consumption despite adequate study power, although an association between ingestion of undercooked meat and infection (odds ratio = 3.5, P less than .05) was found when community controls were used. Proper food cooking (and handling) rather than the avoidance of particular food products is the preventive measure of choice.