A California grower was the source of fresh onions linked to a deadly E. coli food poisoning outbreak at McDonald’s, officials with the restaurant chain said Thursday.

Meanwhile, other fast-food restaurants — including Taco Bell, Pizza Hut, KFC and Burger King — pulled onions from some menus.

McDonald’s officials said that Taylor Farms, of Salinas, California, sent onions to one distribution facility, which led the fast-food chain to remove Quarter Pounder hamburgers from restaurants in several states. McDonald’s didn’t say which facility it was.

An outbreak tied to the burgers has sickened at least 49 people in 10 states, including a person who died, federal health officials have said. Investigators said they were focused on slivered onions as a potential source of the infections.

U.S. Foods, a major wholesaler to restaurants across the country, said Thursday that Taylor Farms had issued a recall this week for peeled whole and diced yellow onions for potential E. coli contamination.

The recalled onions came from a Taylor Farms facility in Colorado, a U.S. Foods spokesperson said.

But the wholesaler also noted that it wasn’t a McDonald’s supplier and that its recall didn’t include any products sold at the fast-food chain’s restaurants.

Taylor Farms did not respond to multiple requests for comment.

Officials with the U.S. Food and Drug Administration did not confirm that the agency is investigating Taylor Farms. A spokesperson said Thursday that the agency is “looking at all sources” of the outbreak.

In the meantime, other national restaurant chains temporarily stopped using fresh onions.

“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.

Onions have been implicated in previous outbreaks. In 2015, Taylor Farms recalled a celery and onion mix used in Costco chicken salads after 19 people were sickened with E. coli.

At least 10 people have been hospitalised in the McDonald’s outbreak, including a child who suffered a severe kidney disease complication as a result of the infection.

Illnesses were confirmed between Sept. 27 and Oct. 11, according to the U.S. Centers for Disease Control and Prevention.

Victims were infected 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, diarrhoea or bloody diarrhoea 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.