• McDonald’s Quarter Pounders are making people sick with E. coli, the CDC said Tuesday.
• One person died and 10 others were hospitalized after eating the hamburgers, the authority said.
• Shares of McDonald’s plunged in an extended range on Tuesday following the announcement.

McDonald’s shares fell more than 9% on Tuesday after the Centers for Disease Control and Prevention said one person died and 10 died in connection with an E. coli outbreak linked to the fast food chain’s Quarter Pounders others were hospitalized.

The health agency said the “rapidly advancing” outbreak is primarily affecting people in Nebraska and Colorado. It added that most of those affected reported eating a Quarter Pounder hamburger.

In an internal memo posted on the company’s website Tuesday, McDonald’s North America chief supply chain officer Cesar Piña said the chain was taking “swift and decisive” action in response to the outbreak. The statement said the illnesses may be linked to the onion slivers used in the Quarter Pounders, which are purchased from a single supplier that supplies three distribution centers.

McDonald’s is temporarily removing the burgers from restaurants in Colorado, Kansas, Utah, Wyoming and parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma, the statement said.

“We take food safety very seriously and it is the right thing to do,” Piña wrote.

A total of 49 cases have been reported in 10 states so far, but the scale of the outbreak is “likely much higher,” the CDC said.

The CDC said McDonald’s has removed some ingredients from its burgers and stopped selling Quarter Pounders in some states. Researchers are working to find out which ingredient makes people sick.

The company’s shares plunged around 9% amid extended training on Tuesday following the announcement.

McDonald’s profits fell 0.7% year-over-year in the second quarter of 2024, compared to growth of 10.3% in the same period in 2023, Business Insider previously reported.

McDonald’s was in the headlines earlier this week after former President Donald Trump appeared at one of its restaurants in Pennsylvania on Sunday to serve customers in the swing state.

E. coli is a bacteria that can make people sick with diarrhea, urinary tract infections, pneumonia and sepsis, according to the Centers for Disease Control. Infections can occur through contact with contaminated water or food, as well as through contact with other people or animals.

According to the CDC, handwashing is the best way to prevent the spread of E. coli.