One person has died and dozens have fallen ill after a serious illness E.coli An outbreak is linked to McDonald’s Quarter Pounder burgers, the U.S. Centers for Disease Control and Prevention (CDC) said Tuesday.

The outbreak, which began in late September, includes 10 western states, with most of the 49 cases concentrated in Colorado and Nebraska, the health department said.

Shares in the fast food chain fell more than six percent in after-hours trading after the announcement.

Ten people have been hospitalized, including one child with hemolytic uremic syndrome – a serious condition that damages the blood vessels in the kidneys.

“One elderly person in Colorado has died,” a CDC statement said.

All affected people carried the same trunk E.coli and reported eating at McDonald’s before developing their symptoms, specifically remembering having Quarter Pounders.

While investigators have not yet identified the exact ingredient causing the outbreak, they are focusing on sliced ​​onions and beef patties — both of which have been removed from restaurants in the affected states pending further investigation.

“Food safety is so important to me and everyone at McDonald’s,” Joe Erlinger, president of McDonald’s USA, said in a video message. “We have taken steps to proactively eliminate the chopped onions used in Quarter Pounders in select states.

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

He added that majority of states are not affected. Other menu items, including other beef products, remain available in affected states.

The agency advised those who consumed a Quarter Pounder and developed symptoms E.coli poisoning – such as diarrhea, fever above 102 degrees Fahrenheit (38.9 C) and vomiting – to seek medical attention.

Symptoms typically begin three to four days after exposure, and most people recover within five to seven days without treatment. However, some cases can become serious and require hospitalization.

© Agence France-Presse