A Colorado farm has recalled onions it may have sold to McDonald’s before the fast-food chain’s E. coli outbreak, which killed one person in the state and sickened at least 49 people nationwide.

Taylor Farms, which is based in California but also grows vegetables in Colorado, issued a recall notice Wednesday for whole and diced yellow onions because of possible E. coli contamination.

McDonald’s stated it had purchased onions from Taylor Farms and distributed them to locations in areas affected by the 10-state outbreak, but distributor U.S. Foods told a different story, saying the recalled vegetables never went to the fast-food chain.

Taylor Farms has yet to comment on the allegations, and the U.S. Department of Agriculture declined to specify what farms and other facilities it was investigating.

Federal officials are investigating slivered onions and quarter-pound beef patties as possible sources of the outbreak. McDonald’s took Quarter Pounders off the menu in Colorado and other affected states, because most people who completed interviews about the foods they ate said they’d had that type of hamburger in the days before they got sick.

According to the Centers for Disease Control and Prevention, at least 26 of the 49 people who have gotten sick nationwide after eating at McDonald’s live in Colorado.

Ten people have needed hospital care.

The one fatality was an unidentified person in Mesa County who had pre-existing health conditions.

Whatever companies supplied and handled contaminated ingredients could face liability.

A Colorado man, Eric Stelly, sued McDonald’s for a minimum of $50,000 because he became ill with E. coli after eating at one of the chain’s locations in Greeley on Oct. 4. Stelly visited an emergency room, but the hospital didn’t keep him overnight. His attorney said he was “still recovering” as of Wednesday.

Most people infected with E. coli recover without specific treatment, but children under 5, adults over 65 and people with compromised immune systems are at a higher risk of complications.

The bacteria produce a toxin that causes abdominal pain, vomiting, bloody diarrhea and, rarely, bloodstream infections or kidney damage.

In the wake of the McDonald’s E. coli outbreak, other national restaurant chains temporarily stopped using fresh onions.

Colorado chain Illegal Pete’s told the Colorado Sun that it was among the restaurants that had purchased the recalled onions and was throwing them out, while Burger King said it was replacing the recalled onions with ones from another supplier.

Taco Bell, Pizza Hut and KFC also had to dispose of their onions in locations that received potentially contaminated shipments,

“As we continue to monitor the recently reported E. coli outbreak, and out of an abundance of caution, we have proactively removed fresh onions from select Taco Bell, Pizza Hut and KFC restaurants,” Yum Brands said in a statement.

Louisville, Kentucky-based Yum Brands wouldn’t say where onions were removed or whether the company uses the same supplier as McDonald’s.

Yum Brands said it will continue to follow guidance from regulators and its suppliers.

Restaurant Brands International, which owns Burger King, said Thursday that 5% of its restaurants use onions distributed by Taylor Farms’ Colorado facility. Burger King restaurants get deliveries of whole, fresh onions and its employees wash, peel and slice them.

Even though it wasn’t contacted by health officials and it had no indications of illness, Restaurant Brands said it asked the restaurants that received onions from the Colorado facility to dispose of them two days ago. The company said it’s restocking with onions from other suppliers.

Bill Marler, an attorney who specializes in foodborne illness cases and is representing clients in Nebraska who got sick after eating at McDonald’s, said Taylor Farms had to recall bags of diced celery and onions in 2015 following cases of E. coli in people who ate chicken salad from Costco.

Contaminated onions also caused a salmonella outbreak in 2023, which sicked at least 80 people, hospitalized 18 and killed one. That outbreak involved a different company, Gills Onions.

In almost all foodborne illness outbreaks, the farms and restaurants didn’t intentionally sell contaminated products, but something in the food safety process broke down, Marler said.

Often, it involves water contaminated by cow feces, such as an irrigation ditch that caught waste from a nearby feedlot, he said.

The strain of E. coli involved in the current outbreak is harmless to cattle but can cause severe symptoms in humans.

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.

“Usually in these cases, there’s a cow somewhere,” Marler said.

The Associated Press contributed to this report.