The U.S. Food and Drug Administration continues to believe that slivered onions from a single supplier are the likely source of contamination, McDonald’s said in a statement. It said it will resume selling the Quarter Pounder at affected restaurants —- without slivered onions — in the coming week.

As of Friday, the outbreak had expanded to at least 75 people sick in 13 states, federal health officials said. A total of 22 people had been hospitalized, and two developed a dangerous kidney disease complication, the Centers for Disease Control and Prevention said. One person has died in Colorado.

Early information analyzed by the FDA showed that uncooked slivered onions used on the burgers “are a likely source of contamination,” the agency said. McDonald’s has confirmed 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 had come from a facility in Colorado Springs, Colorado.

McDonald’s pulled the Quarter Pounder burger from menus in several states — mostly in the Midwest and Mountain states — when the outbreak was announced Tuesday. McDonald’s said Friday that slivered onions from the Colorado Springs facility were distributed to approximately 900 of its restaurants, including some in transportation hubs like airports.

The company said it removed slivered onions sourced from that facility from its supply chain on Tuesday. McDonald’s said it has decided to stop sourcing onions from Taylor Farms’ Colorado Springs facility “indefinitely.”

The 900 McDonald’s restaurants that normally received slivered onions from Taylor Farms’ Colorado Springs facility will resume sales of Quarter Pounders without slivered onions, McDonald’s said.

Testing by the Colorado Department of Agriculture ruled out beef patties as the source of the outbreak, McDonald’s said.

The department of agriculture received multiple lots of fresh and frozen beef patties collected from various Colorado McDonald’s locations associated with the E. coli investigation. All samples were found to be negative for E. coli, the department said.

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

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

Colorado had the most illnesses reported as of Friday, with 26 cases. At least 13 people were sickened 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 it didn’t pull the Quarter Pounder from any additional restaurants and noted that some cases in states outside the original region were tied to travel.

The CDC said some people who got sick reported traveling to other states before their symptoms started. At least three people said they ate at McDonald’s during their travel. Illnesses were reported between Sept. 27 and Oct. 11.

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

Symptoms of E. coli poisoning can occur quickly, within a day or two of eating contaminated food. They typically include fever, vomiting, diarrhea or bloody diarrhea and signs of dehydration — little or no peeing, increased thirst and dizziness. The infection is especially dangerous for children younger than 5, people who are elderly, pregnant or who have weakened immune systems.