Ten people have been hospitalized and one person has died after E. coli infections linked to McDonald’s Quarter Pounder hamburger in 10 states, the U.S. Centers for Disease Control said on Tuesday.

The death was reported in an older person in Colorado, and one child has been hospitalized with severe kidney complications, the CDC reported.

Forty nine people from 10 states have fallen sick from the same strain of E. coli, the CDC said. Most sick people are from Colorado or Nebraska.

Everyone interviewed in connection with the outbreak had reported eating at McDonald’s before falling ill and most mentioned eating Quarter Pounder hamburgers, the CDC said. The U.S. Agriculture Department, the Food and Drug Administration and state health officials are also investigating.

Cesar Piña, McDonald’s North American chief supply chain officer, said in an online statement that initial findings from the investigation have traced a subset of the infections to slivered onions “sourced by a single supplier that serves three distribution centers.”

Out of an abundance of caution, Piña said, McDonald’s has removed the quarter pounder hamburgers from its menus in the affected area, which includes Colorado, Kansas, Utah and Wyoming, as well as portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma.

Distribution of all slivered onions in the area has been paused and all local restaurants have been instructed to remove the product from their supply, he added.

McDonald’s USA president Joe Erlinger said in a video statement all other beef products are unaffected.

“I hope these steps demonstrate McDonald’s’ commitment to food safety,” he said.

Global News has asked McDonald’s Canada if any affected ingredients have been pulled from Canadian stores.

A Health Canada spokesperson referred Global News to its online listing of active outbreak investigations, which does not include any mention of E. coli infections at McDonald’s restaurants in Canada.

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E. coli bacteria are harbored in the guts of animals and found in the environment. Infections can cause severe illness, including fever, stomach cramps and bloody diarrhea.

People who develop symptoms of E. coli poisoning should seek health care immediately and tell the provider what they ate.

The news comes in an already tough year for the Chicago-based chain. Its global same-store sales fell for the first time in nearly four years in the second quarter as inflation-weary customers skipped eating out or chose cheaper options. The company responded with a $5 meal deal, which was introduced at U.S. restaurants in late June and was recently extended through December. The deal doesn’t include the Quarter Pounder.

McDonald’s shares dropped 9% in after-hours trading Tuesday after the CDC’s announcement.

In 2015, burrito chain Chipotle saw its sales battered and reputation hit due to E.coli outbreaks in several states.

The type of bacteria implicated in this outbreak, E. coli O157:H7, causes about 74,000 infections in the U.S. each year, leading to more than 2,000 hospitalizations and 61 deaths. Infections are especially dangerous for children younger than 5 and can cause acute kidney failure.

—With files from the Associated Press and Global News