McDonald's is trying to pinpoint the cause of a deadly E. coli outbreak linked to its Quarter Pounder hamburgers.
While a specific ingredient has not yet been confirmed as the source of the outbreak, a preliminary investigation by the Food and Drug Administration suggests fresh, slivered onions that are served raw on Quarter Pounder hamburgers were a likely source of the contamination.
Other burgers, like the Big Mac, use diced, cooked onions.
The outbreak has killed one person and 75 others have fallen ill from E.coli strain O157:H7, according to the Centers for Disease Control and Prevention. At least 22 people had to be hospitalized and two people developed hemolytic uremic syndrome, a serious condition that can cause kidney failure.
A total of 13 states are now affected by the outbreak, with most illnesses reported in Colorado, Montana and Nebraska. Others states include: Iowa, Kansas, Michigan, Missouri, New Mexico, Oregon, Utah, Washington, Wisconsin and Wyoming.
The most recent illness started on October 10, and officials expect the case count to rise as more people learn about the outbreak.
While the investigation is ongoing, Taylor Farms, the supplier of slivered onions for the affected McDonald's locations, has initiated a voluntary recall of yellow onions.
"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," the agency said in a statement.
The Food Safety and Inspection Service is also conducting traceback on hamburger patties served at McDonald's in affected states to determine if ground beef is a source of illness.
McDonald's has also temporarily stopped selling Quarter Pounders in affected states, roughly one-fifth of its U.S. stores, as a result of the outbreak, including in: Colorado, Kansas, Utah, Wyoming, and portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma. According to company leadership, most other menu items are not involved in the outbreak.
Consumers who have already eaten at McDonald's and have symptoms of E. coli infection should contact their health care provider and receive care immediately.
Symptoms begin anywhere from a few days after consuming contaminated food or up to nine days later. Symptoms include severe stomach cramps, diarrhea, fever, nausea, and/or vomiting. Some infections can cause severe bloody diarrhea and lead to life-threatening conditions, such as a type of kidney failure called hemolytic uremic syndrome (HUS), or the development of high blood pressure, chronic kidney disease, and neurologic problems.