CNN
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The U.S. Centers for Disease Control and Prevention issued a food safety alert Tuesday regarding an E. coli outbreak they say is linked to McDonald’s Quarter Pounders.

At least 49 illnesses, including one death of an elderly person, have been reported in 10 states. Ten people have been hospitalized, including a child with hemolytic uremic syndrome, a serious complication that can arise from an E. coli infection. Most diseases occur in Colorado and Nebraska.

Most people who got sick reported eating McDonald’s Quarter Pounder sandwiches, the CDC says.

The agency says the investigation is “rapidly evolving” and that information from the U.S. Food and Drug Administration indicates chopped onions are a likely source of contamination.

McDonald’s has stopped using onion and quarter-pound beef patties in several states as the investigation continues, the CDC says. According to the agency, the beef patties are only used for the Quarter Pounders, and the chopped onions are primarily used for the Quarter Pounder and not for other items.

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

“We are working closely with our suppliers to replenish inventory for the Quarter Pounder over the coming weeks (timing will vary by local market),” the report said. “In the meantime, all other menu items, including other beef items (including the Cheeseburger, Hamburger, Big Mac, McDouble and the Double Cheeseburger) remain unaffected and available.”

According to the FDA, McDonald’s has removed the sliced ​​onions and quarter-pound patties from stores in Colorado, Kansas, Utah, Wyoming and parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma. Quarter Pounder burgers may not be available in other states.

However, the CDC also notes that the outbreak may extend beyond these states.

People with E. coli infections may have 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 become ill recover within a week without treatment, others may develop serious kidney problems and require hospitalization.

Anyone who becomes ill after eating a McDonald’s Quarter Pounder should seek medical attention and tell the provider what he or she ate, the CDC says.

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

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