Shares of McDonald’s (MCD) plummeted in extended trading Tuesday after U.S. health authorities said they were investigatin꧟g an E. coli outbreak possibly linked to the burger chain’s Quarter Pounder. 

The Centers for Disease Control and Prevention (CDC) said in a statement Tuesday that 49 cases of E. coli infection had been reported across 10 states. Ten known cases have resulted in hospitalization and 1 death has been reported. 

“Most people in this outbreak are reporting eating ꧂the Quarter Pounder hamburger at McDonald’s before becoming sick. It is not yet known which specific food ingredient is contaminated,” the agency said. 

Regulators said McDonald’s is collaborating with their investigation, and stopped offering slivered onions and quarter-pound hamburger patties in sಌeveral states. Cases have been concentrated in Colorado and Nebraska, according to the CDC. 

Product Removed ꦗFrom Restaurants in Several States

Cesar Piña, the fast food chain's North America Supply Chain Officer, said in an internal message posted on the company's website that McDonald's is taking "swift and decisive action."

Piña said that initial findings in꧑dicate that some of the illnesses may be linked to slivered onions from a single supplier. In response, the company is suspending the distribution of slivered onions and removing Quarter Pounders from restaurants in Colorado, Kansas, Utah and Wyoming, as well as those in parts of Idaho, Iowa, Missouri, Montana, Nebraska, ༒Nevada, New Mexico and Oklahoma.

"The decision to do this is not one we take lightly, and it was made in close consultation with the CDC," McDonald's USA President Joe Erlinger said in a video message. He noted that the majority of McDonald's products are not affected.

Shares of McDonald's were down 6.5% in extended trading about two hours after the closing bell. The stock had fallen nearly 10% shortly after the CDC release.

UPDATE—Oct. 22, 2024: This article has been updated to include comments from McDonald's executives and recent share price activity.