On October 22, 2024, the CDC reported that public health and regulatory officials in several states, the FDA, and the USDA-FSIS are investigating a multistate outbreak of E. coli O157:H7 infections. Epidemiologic data show that Quarter Pounder hamburgers served at McDonald's are contaminated with E. coli, making people sick. Early information from the FDA indicates onions may be a source of this outbreak. Investigators from all agencies are working quickly to determine the contaminated ingredient. As of October 22, 49 people infected with the outbreak strain of E. coli O157:H7 have been reported from 10 states. Illnesses started from September 27, 2024, to October 11, 2024. Of 28 people with information available, 10 have been hospitalized, and one person developed hemolytic uremic syndrome. One death has been reported from an older adult in Colorado. This is not the same person with HUS. Of the 18 people interviewed, all 18 (100%) reported eating at McDonald's, and 16 reported eating a beef hamburger. Of 14 people who remember the beef hamburger they ate at McDonald's, 12 (86%) reported eating a Quarter Pounder hamburger. Some people in this outbreak reported traveling to other states before their illness started. At least one person ate at McDonald's during their travel. Investigators are working to determine if the slivered onions or beef patties in Quarter Pounder burgers are the specific source of this outbreak. Preliminary traceback information reviewed by the FDA shows that slivered onions served on Quarter Pounders are a likely source of contamination. FDA is working quickly to confirm that these onions are a source of this outbreak and to determine if these onions were served or sold at other businesses. FSIS is conducting a traceback of hamburger patties served at McDonald's to determine if ground beef is a source of illness. Mcdonald's has stopped using fresh slivered onions and quarter pound beef patties in several states to protect their customers while a source of illness is confirmed. @ https://www.cdc.gov/ecoli/outbreaks/investigation-update-e-coli-o157-2024.html