Fast food giants have pulled fresh onions from their US menus after an E.coli outbreak at McDonald’s killed one person and sickened 49 others.

McDonald’s, as well as its rivals, including Burger King, KFC, Pizza Hut and Taco Bell, have gone all out, removing fresh onions from their menus at select US branches.

The ingredient is believed to be the likely source of the outbreak that led to McDonald’s takes out a quarter of a pound from a fifth of its US restaurants.

The onions are said to have come from Taylor Farms, a California company.

Beef shanks are now also under scrutiny from regulators who are investigating whether they could also be affected.

However, when beef is properly cooked, the E.coli is killed – while a quarter pounder is served with raw onions.

The popular burger has been pulled from restaurants in states including Colorado, Kansas, Utah and Wyoming, and parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma.

At least ten people were hospitalized in the McDonald’s outbreak, including a child who suffered a severe complication of kidney disease as a result.

The illnesses were confirmed between September 27 and October 11, according to the US Centers for Disease Control and Prevention.

“They’re not on our menu”

About 5 percent of Burger King locations in the U.S. have also pulled the ingredient from the menu, a company spokesman said.

Eric Stelly, of Greeley, Colorado, is suing McDonald’s after contracting an E.coli infection.

In a lawsuit, he said he ate at McDonald’s on Oct. 4 before falling ill two days later and seeking emergency care — health officials later confirmed his infection was part of the outbreak.

McDonald’s said Thursday that Taylor Farms supplied the onions.

The US Food and Drug Administration (FDA) confirmed that Taylor Farms was the supplier and added: “Yellow onions were sold to additional food service customers.”

An FDA spokesman said: “Customers who received recalled onions have been notified directly of the recall.”

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Major food distributors, including US Foods and Sysco Corp, also notified customers of the recall.

A service manager at a Burger King in Colorado said, “The company has told us not to use any onions for the foreseeable future. They are off our menu.”

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Onions have been implicated in previous outbreaks, and in 2015 Taylor Farms recalled a celery and onion mix used in Costo chicken salads after 19 people became ill with E.coli.

Then last year, 80 people got sick and one person died in a salmonella outbreak linked to diced onions from Gills Onions in Oxnard, California.