One person has died and dozens have been sickened by E. coli food poisoning linked to McDonald’s Quarter Pounder burgers in several U.S. states, federal health authorities said Tuesday.

The outbreak – which began in September – has spread across 10 Western states, with at least 49 infections reported, the US Centers for Disease Control (CDC) said.

“Epidemiological data show that Quarter Pounder burgers served at McDonald’s are contaminated with E. coli and are making people sick,” the CDC said.

The highest number of cases are concentrated in Colorado and Nebraska. Other affected states include Iowa, Kansas, Missouri, Montana, Oregon, Utah, Wisconsin and Wyoming.

Ten people have been hospitalized, including one child with serious kidney complications, according to the CDC.

“One older person in Colorado has died,” the CDC added.

Most remember eating Quarter Pounders

All of the people surveyed about the infections reported eating at McDonald’s before becoming ill.

Most of them mentioned eating the popular Quarter Pounder hamburger, the CDC said.

The bacterial strain in question, E. coli O157:H7, can cause serious illness. It was also the cause of an outbreak in 1993 when four children died after eating undercooked hamburgers at Jack in the Box restaurants.

“Initial information from the Food and Drug Administration (FDA) indicates that onions may be a source of this outbreak. Investigators from all agencies are working quickly to determine the contaminated ingredient,” the CDC said.

What did McDonald’s say?

McDonald’s share price tumbled more than 6% in extended trading after the world’s largest food chain was linked to the E. coli outbreak.

“Food safety is so important to me and everyone at McDonald’s,” McDonald’s USA President Joe Erlinger said in a video message.

The company has suspended distribution of the chopped onions and temporarily removed the Quarter Pounder from the menu in the affected areas.

Additionally, the Quarter Pounder has also been temporarily removed from the menu in parts of Idaho, Nevada, New Mexico and Oklahoma.

“We have taken steps to proactively eliminate the chopped onions used in Quarter Pounders in certain states,” Erlinger said.

“We have also made the decision to temporarily remove the Quarter Pounder from restaurants in certain states,” he added.

dvv/zc (AP, AFP, Reuters, dpa)