FDA Closes Investigation of McDonald’s E. Coli Outbreak Without Tests Confirming Onions as Source
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The U.S. Centers for Disease Control and Prevention (CDC) has announced that the Escherichia coli outbreak linked to yellow onions distributed by Taylor Farms and served at McDonald’s restaurants to be over, and the U.S. Food and Drug Administration (FDA) has closed its investigation.
Although the outbreak strain of Shiga toxin-producing E. coli O157:H7 (STEC O157:H7) was not confirmed in any product or environmental samples, FDA has concluded yellow onions to be the likely source of the outbreak based on traceback and epidemiologic evidence.
Outbreak Timeline
The outbreak investigation was opened on October 22, 2024 after a string of illnesses were reported in people who consumed McDonald’s Quarter Pounder sandwiches. By the close of the outbreak investigation on December 3, a total of 104 people infected with the outbreak strain of E. coli O157:H7 were reported from 14 states, mostly in the U.S. West and Midwest, with the exception of North Carolina. Of 98 people with information available, 34 were hospitalized, four people developed hemolytic uremic syndrome (HUS), and one person (not one of the HUS patients) died.
Traceback investigation conducted by FDA pointed to fresh, slivered onions served on McDonald’s burgers as the vehicle of illness in the outbreak, causing national restaurant chains to pull onions from their menus out of an abundance of caution. Soon after, FDA confirmed one Taylor Farms facility in Colorado Springs, Colorado to be the supplier of the implicated onions, which the agency affirmed was the probable cause of the outbreak. Taylor Farms initiated a voluntary recall.
Meanwhile, testing of burger patties from McDonald’s Quarter Pounders showed no trace of E. coli, ruling the meat out as the vehicle of illness, and CDC named yellow onions served at McDonald’s as the cause of the foodborne illness outbreak.
Despite FDA’s and CDC’s assertion that yellow onions were the vehicle of illness, all environmental samples from McDonald’s restaurants, distribution centers, and companies of interest tested negative for the outbreak strain of STEC O157:H7. A single sample of recalled onions and one environmental sample from a grower—which FDA could not implicate in the outbreak—tested positive for E. coli, but neither sample matched the outbreak strain or any other clinical illnesses. Additional samples from the investigation were analyzed and resulted negative for E. coli.
Still, FDA and CDC maintain that epidemiologic and traceback data point to yellow onions as the vehicle of illness in the outbreak. Of the 81 people interviewed who were sickened in the outbreak, 80 (99 percent) reported eating at McDonald's. Additionally, 75 people were able to remember specific menu items they ate at McDonald's, of which 63 (84 percent) reported a menu item containing fresh, slivered onions.
As of December 3, the outbreak is considered over by CDC, and FDA has closed its investigation.
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