The US Centers for Disease Control and Prevention issued a food safety alert Tuesday warning dozens of people reported eating the Quarter Pounder sandwich at McDonald's before becoming sick.
The E. coli outbreak has led to 75 illness across 13 states, including 22 hospitalizations and one death, according to the latest information from the CDC, with most of the related illnesses occurring in Colorado.
A specific ingredient has not been confirmed as the source of the outbreak, federal agencies said Friday, but the US Food and Drug Administration previously said the slivered onions or beef patties on Quarter Pounder sandwiches are the likely source of contamination.
On Sunday, the Colorado Department of Agriculture said McDonald's beef patties used for the Quarter Pounder tested negative for E. coli. The department tested fresh patties from restaurants associated with the outbreak.
Based on the findings from the Colorado agriculture department and after comparing CDC data with its own supply chain data, McDonald's is confident in ruling out fresh beef patties as a source of contamination, according to a Sunday news release.
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The company is now asking beef suppliers to produce a new supply of fresh beef patties, and the Quarter Pounder is expected to be available in all restaurants in the coming week, the release said.
The 900 restaurants that received slivered onions from McDonald's supplier Taylor Farms' Colorado Springs facility will resume sales of Quarter Pounders without slivered onions, the release added. "Those restaurants are in Colorado, Kansas, and Wyoming, as well as portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, Oklahoma, and Utah," it said.
The FDA and CDC say they are continuing to work with partners to investigate the source of the outbreak. CNN has reached out to the FDA to see if it has ruled out beef patties as the source of the E. coli outbreak. When contacted by CNN on Sunday, the CDC referred back to its Friday release, which does not specify a specific ingredient as the cause.
"The FDA is using all available tools to confirm if onions are the source of this outbreak," a spokesperson said previously. "FDA and state partners are also collecting onion samples for analysis."
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Taylor Farms removed yellow onions from the market "out of an abundance of caution," the company said in a statement Wednesday, and distributor US Foods has issued a recall of four onion products due to "potential E. coli contamination."
"I know that our relationship is built on trust," McDonald's US President Joe Erlinger said in a video message posted Sunday. "You trust us to serve you safe food every time."
"On behalf of the McDonald's system, I want you to hear from me: we are sorry," Erlinger added. "For those customers affected, you have my commitment that, led by our values, we will make this right."