An outbreak of E. coli O157:H7 infections traced to slivered onions on McDonald’s Quarter Pounder hamburgers has been declared over.
As of Dec. 3, the Centers for Disease Control and Prevention had confirmed 104 patients from 14 states. The CDC reported that 38 people required hospitalization and one patient died. Four patients developed hemolytic uremic syndrome (HUS), a serious condition that can cause kidney failure.
There were likely many more sick people in this outbreak because the CDC reports that for every confirmed patient in an E. coli O157:H7 outbreak there are 26 who go undiagnosed. This is because some people do not seek medical attention and others are not specifically tested for E. coli.
Patients became ill from mid-September through Oct. 21. Of 81 people interviewed, 80 reported eating at McDonald’s before becoming ill. Seventy-five patients were able to remember specific menu items they ate at McDonald’s, of which 63 reported a menu item containing fresh, slivered onions.
The outbreak was traced to onions from Taylor Farms. The company recalled its yellow onions on Oct. 22. By then, McDonald’s had stopped serving slivered onions on its products and temporarily stopped serving Quarter Pounders at some of its restaurants. Ground beef was tested and came back negative for E. coli contamination.
The Food and Drug Administration, the Colorado Department of Agriculture, and Colorado Department of Public Health and Environment collected several product and environmental samples during the outbreak investigation. One FDA sample of recalled onions and one environmental sample from a grower tested positive for E. coli, but they were non-O157:H7 E. coli and did not match the outbreak strain or any other clinical illnesses. However, epidemiologic and traceback evidence shows that recalled, yellow onions were the likely source of this outbreak.
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