Los Angeles — McDonald’s announced Sunday that Quarter Pounders will again be on its menu at hundreds of its restaurants after testing ruled out beef patties as the source of the outbreak of E. coli poisoning tied to the popular burgers that killed one person and sickened at least 75 others across 13 states.

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 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 and people who are elderly, pregnant or who have weakened immune systems. 

McDonald’s says they believe slivered onions supplied from a California-based produce company have been isolated as the likely cause of the E. Coli outbreak tied to the company’s Quarter Pounders.

Early information analyzed by the FDA showed that uncooked slivered onions used on the burgers “are a likely source of contamination,” the agency said.

The company says the onions were distributed from Taylor Farms’ Colorado Springs facility and historically 900 restaurants have received onion supplies from Taylor Farms.

The 900 restaurants that have historically received onions from Taylor Farms are in states which include Colorado, Kansas, and Wyoming, as well as portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, Oklahoma, and Utah. Texas is not included in the list.

“The issue appears to be contained to a particular ingredient and geography, and we remain very confident that any contaminated product related to this outbreak has been removed from our supply chain and is out of all McDonald’s restaurants,” said McDonald’s North America Chief Supply Chain Officer Cesar Piña.

McDonald’s said testing was done over the weekend by the Colorado Department of Agriculture which did not detect E. Coli in samples taken of Quarter Pounder beef patties from restaurants in the area.

“Overlaying the CDC’s Epidemiological data with our Supply Chain traceback data, we have ruled out Quarter Pounder patties as the source,” Piña said. “Last week, out of an abundance of caution, we stopped distributing Quarter Pounder beef patties to the impacted area. Based on the above information, we are now confident in asking our beef suppliers to produce a new supply of fresh beef patties for the impacted areas. We will resume distribution of that fresh supply and the Quarter Pounder is expected to be available in all restaurants in the coming week.”

Piña says the 900 restaurants that received slivered onions in the affected area will start selling Quarter Pounders again, just without the onions.

“The FDA is continuing its investigation into Taylor Farms’ Colorado Springs facility. As a reminder, McDonald’s removed slivered onions from this facility from our supply chain on October 22 and shared that we had decided to stop sourcing onions from Taylor Farms’ Colorado Springs facility indefinitely. Over the past few days, you’ve likely seen that additional food service providers and restaurant brands that received onions from this facility have moved to stop selling and/or recall onions,” Piña said.

McDonald’s President Joe Erlinger thanked employees, governmental agencies, and franchisees and restaurant teams for helping to find and contain the issue.

“Because of your work, this issue was quickly identified and contained. Because of your work, our customers can be confident that any contaminated product related to this outbreak has been removed from our supply chain. Because of your work, we can confidently say that it’s safe to eat at McDonald’s restaurants. To all: I hope our actions and today’s steps demonstrate McDonald’s continued commitment to food safety and the strong partnership that we cherish having with each of you,” Erlinger said in a video message.

On Friday, federal officials said at least 75 people had been sickened from the outbreak. One person in Colorado died.

McDonald’s Quarter Pounder hamburgers have been linked to an outbreak of E. coli, a bacteria that can make people sick.

The outbreak has killed one person in Colorado, according to the U.S. Centers for Disease Control and Prevention. It has also affected nearly 50 other people in 10 states.

The illnesses may be linked to slivered onions used on Quarter Pounders or the patty itself, but the investigation into the specific contaminated food ingredient is ongoing, the CDC shared in a post Tuesday.

McDonald’s said it has removed Quarter Pounders from a total of 12 states, but that all other menu items are unaffected.

The CDC added the outbreak may not be limited to the states with known illnesses, either.

“The true number of sick people is likely much higher than the number reported. This is because many people recover without medical care and are not tested for E. coli,” the agency wrote.

Symptoms and early signs of E. coli

E. coli symptoms usually start about two to seven days after exposure, CBS News chief medical correspondent Dr. Jon LaPook said on the “CBS Evening News” Tuesday.

Symptoms can include:

• Diarrhea
• Fever
• Abdominal cramping
• Vomiting
• Feeling dehydrated or dizzy

If you ate a Quarter Pounder and have any of these symptoms, contact your health care provider, the CDC advises. 

“Especially if you have fever over 102, you can’t keep liquids down or your symptoms are lasting more than three days,” LaPook said. 

How E. coli is transmitted

People can get infected with E. coli by ingesting it.

“This can happen through contaminated food or water or contact with animals, environments, or other people,” the CDC’s website notes.

The best way to prevent infection is by keeping your hands clean, preparing food safely and drinking safe water, the agency adds.

How severe can E. coli get

“Most E. coli are harmless and are part of a healthy intestinal tract. E. coli help us digest food, produce vitamins, and protect us from harmful germs. But some E. coli can make people sick with diarrhea, urinary tract infections, pneumonia, sepsis, and other illnesses,” the CDC says. 

For example, certain E. coli infections can lead to a serious health condition called hemolytic uremic syndrome, or HUS, which can cause kidney failure, permanent health problems and death, according to the CDC.

Certain people are also at increased risk for E. coli infection, including: 

• Children under 5
• Adults 65 and older
• People with weakened immune systems
• International travelers