The U.S. Centers for Disease Control and Prevention issued a food safety alert Tuesday regarding an E. coli outbreak it said was linked. McDonald’s Quarter Pounders.

At least 49 illnesses were reported in 10 states; one of which was the death of an elderly person. Ten people were hospitalized, including a child with hemolytic uremic syndrome, a serious complication of E. coli infection. Most of the disease is in Colorado and Nebraska.

The CDC reported that most of the people who got sick ate McDonald’s Quarter Pounder sandwiches.

The agency said the investigation was “moving quickly” but did not identify any specific context. But the researchers are focusing on two ingredients: sliced ​​onions and beef patties. According to the agency, beef patties are used only for Quarter Pounders, and onions are used primarily for Quarter Pounders and not for other products.

McDonald’s said in a statement that initial investigation findings linked the ingredients to “a single supplier serving three distribution centers.”

“We are working closely with our suppliers to renew supply of the Quarter Pounder in the coming weeks (timing will vary depending on local market),” he said. “In the meantime, all other menu items, including other beef items (including the Cheeseburger, Hamburger, Big Mac, McDouble and Double Cheeseburger), will not be affected and will remain available.”

According to the CDC, McDonald’s removed the ingredients from its stores in Colorado, Iowa, Kansas, Missouri, Montana, Nebraska, Oregon, Utah, Wisconsin and Wyoming. Quarter Pounder burgers may not be available in other states.

However, the CDC also states that the epidemic may spread beyond these states.

People with E. coli infection may experience symptoms such as severe stomach cramps, diarrhea, fever and vomiting. Symptoms of infection usually begin three or four days after ingesting the bacteria. Although most people who get sick recover within a week without treatment, some may develop serious kidney problems and require hospitalization.

The CDC says anyone who becomes sick after eating a McDonald’s Quarter Pounder should seek medical attention and tell the provider what they ate.

McDonald’s said in its statement that “serving customers safely every day, in every restaurant, is our top priority” and that it will continue to work with the CDC on the investigation.

McDonald’s stock price fell sharply in after-hours trading after news of the outbreak broke.

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