A deadly outbreak of E. coli poisoning affiliated with McDonald’s Quarter Pounders has expanded, with at least 75 sick people in 13 states, federal health officials said Friday.

A total of 22 people are now hospitalized, and two have developed a dangerous complication of kidney disease, according to the Centers for Disease Control and Prevention. One person has died in Colorado.

No definitive source of it the outbreak has been identified, U.S. Food and Drug Administration officials said. Early information analyzed by the FDA showed that uncooked chopped onions used on the burgers “are a likely source of contamination,” the agency said.

McDonald’s has confirmed this that Taylor Farms, a California-based produce company, was the supplier of the fresh onions used in the restaurants involved in the outbreak, and that they came from a facility in Colorado Springs, Colorado.

“We have decided to indefinitely stop sourcing onions from the Taylor Farms facility in Colorado Springs,” McDonald’s said in a statement released Friday.

Taylor Farms said Friday that it has preemptively recalled yellow onions sent from its Colorado factory to its customers and continues to cooperate with the CDC and FDA as they investigate.

“It saddens us to see the diseases and the individuals and families affected,” the family-owned company said after the outbreak.

McDonald’s pulled the Quarter Pounder burger from menus in several states — mainly the Midwest and Mountain states — when the outbreak was announced Tuesday. McDonald’s said Friday that chopped onions from its Colorado Springs plant have been distributed to about 900 of its restaurants, including some in transportation hubs such as airports.

The new cases reported Friday were a sharp increase from the original number of 49 in 10 states. The most illnesses were reported in Colorado, with 26 cases. At least 13 people fell ill in Montana, 11 in Nebraska, 5 each in New Mexico and Utah, 4 each in Missouri and Wyoming, two in Michigan and one each in Iowa, Kansas, Oregon, Wisconsin and Washington, the CDC reported.

McDonald’s said Friday that it has not removed the Quarter Pounder from additional restaurants due to the increase in cases reported by the CDC. The company noted that some cases in states outside the original region were related to travel.

The CDC said some people who became ill reported traveling to other states before their symptoms started. At least three people said they ate at McDonald’s during their trip. Illnesses were reported between September 27 and October 11.

Taylor Farms directly notified its customers of the onion recall but did not tell the public about it, an FDA official said. Companies often issue press releases and the FDA sends out public notices for recalls, but these are not mandatory.

While it remains unclear whether the recalled onions were the source of the outbreak, several other fast-food restaurants — including Taco Bell, Pizza Hut, KFC and Burger King — have removed onions from some menus in certain areas this week.

Restaurant Brands International, owner of Burger King, said 5% of its restaurants use whole onions distributed by Taylor Farms’ facility in Colorado. They are washed, peeled and cut into slices by employees.

Although health officials had not been contacted and there was no indication of illness, Restaurant Brands said it had asked restaurants that received onions from the Colorado plant to get rid of them.

The outbreak involves infections with E. coli 0157:H7, a type of bacteria that produces a dangerous poison. It causes about 74,000 infections in the U.S. annually, leading to more than 2,000 hospitalizations and 61 deaths annually, according to CDC.

People sickened by the outbreak have already moved to sue McDonald’s, according to court records. According to her lawsuit, Clarissa DeBock ate food at a local McDonald’s in Nebraska on September 18, became ill on September 23 and sought emergency care two days later before she was diagnosed with an E. coli infection.

Symptoms of E. coli poisoning can occur quickly, within a day or two of eating contaminated food. They usually include fever, vomiting, diarrhea or bloody diarrhea and signs of dehydration – little or no urination, increased thirst and dizziness. The infection is especially dangerous for children under 5 years old, the elderly, pregnant people or people with a weakened immune system.

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AP business reporter Dee-Ann Durbin provided reporting from Detroit.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.