Dozens of people across the U.S. have contracted E. coli traced to ingredients in McDonald's Quarter Pounders, the Centers for Disease Control and Prevention (CDC) said Tuesday.
So far, 49 people from 10 states have fallen ill with a strain known as E. coli O157:H7, which causes a severe intestinal infection in humans.
Most of the cases have been in Colorado, which has 27 reported cases, and Nebraska, which has nine reported cases, according to the CDC.
Ten people have been hospitalized, including a child with complications from hemolytic uremic syndrome (HUS) -- a disease that affects the kidneys. An older person in Colorado has died, according to the CDC.
Every patient interviewed by the CDC said they ate at McDonald's before falling ill and most said they ate Quarter Pounder hamburgers, specifically.
It's not clear which ingredient is responsible for the illnesses, but CDC investigators are focused on two ingredients: fresh, slivered onions and fresh beef patties.
McDonald's told the CDC it has removed slivered onions and beef patties used for Quarter Pounder hamburgers from stores in the states where cases have been reported, the federal health agency said. As a result, the CDC said Quarter Pounders won't be available for sale in some states.
Although most E. coli bacteria are harmless and are part of a healthy intestinal tract, some strains of the bacteria can make people sick, according to the CDC.
E. coli symptoms often begin three to four days after ingesting the bacteria and include severe stomach cramps, diarrhea that may be bloody and vomiting.
Most people recover on their own within five to seven days, but some people may develop HUS and require hospitalization.
The CDC urges those who are experiencing severe E. coli symptoms and recently ate a McDonald's Quarter Pounder to contact their health care provider immediately.
In a statement on Tuesday evening, McDonald's North America Chief Supply Chain Officer Cesar Piña said that the fast food chain believes the outbreak is linked to slivered onions "used in the Quarter Pounder and sourced by a single supplier that serves three distribution centers."
"As a result, and in line with our safety protocols, all local restaurants have been instructed to remove this product from their supply and we have paused the distribution of all slivered onions in the impacted area," the statement read, in part. "We will continue to work with the Centers for Disease Control and Prevention and are committed to providing timely updates as we restore our full menu."