McDonald’s has stopped selling Quarter Pounder burgers in 20 percent (that’s a fifth) of its stores in the US Burgers have been linked to the E. Coli outbreak in 10 states.

The fast-food chain has removed the burgers from its menu in Colorado, Kansas, Utah, Wyoming and some areas in Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma, the news outlet reported Associated Press reported.

This came after one person died and dozens fell ill from E-coli infections, which the US Centers for Disease Control (CDC) linked to the Quarter Pounder burgers in 10 US states.

said McDonald’s US boss Joe Erlinger NBC‘S Today show Wednesday that it has taken steps to quickly remove the Quarter Pounder from its menu in the areas where the outbreak occurred.

“Given the recent events of the last 24 hours, our priority is to strengthen the confidence of American consumers,” he said.

He further said it was likely that the unidentified contaminated product had already passed through the company’s supply chain.

CDC spokesman Tom Skinner was quoted by the news agency Reuters that the department expects further E-Coli infections.

“McDonald’s took action fairly quickly to hopefully prevent as many cases as possible,” he added.

When asked why McDonald’s did not close restaurants, the company responded that the government’s investigation found no evidence of deficiencies in food preparation.

Preliminary investigations by the U.S. Food and Drug Administration found that freshly sliced ​​onions served raw in the Quarter Pounder burgers were likely a source of contamination.

Notably, McDonald’s also serves raw, sliced ​​onions in one of its breakfast sandwiches, but that sandwich is not available at affected stores. Other burgers, like the Big Mac, use diced, cooked onions, Associated Press reported. It was said that they were looking for a new regional supplier of fresh onions.

The fast food store said it has been working closely with federal food safety regulators since late last week, when it was alerted to the possible E-Coli outbreak.

It said the scale of the problem and the popularity of its products had complicated efforts to identify the source of the contamination. The Associated Press reported.

Notably, McDonald’s has 14,000 locations across the United States and serves over one million Quarter Pounder burgers every two weeks in affected states.