No E. coli was detected in samples of beef patties used in McDonald’s Quarter Pounders that have been linked to a deadly outbreak, a company spokesman said Sunday, citing tests by the Colorado Department of Agriculture.

The department no longer plans to test the beef patties, a company spokesman said, and the patties have been ruled out as the source of the outbreak.

The most likely source of contamination was onions cut from a single source, the company spokesman said, citing the Food and Drug Administration.

McDonald’s stopped sourcing cut onions from that source — Taylor Farms Colorado Springs — indefinitely Sunday, a company spokesman said, days after it pulled Taylor Farms onions from its supply chain.

Taylor Farms’ onions were sold in stores in Colorado, Kansas, Wyoming and parts of other states in the area, the spokesman said. Some of these locations include airports, which may represent cases in other states.

A McDonald’s spokesman said the company is confident it is asking its beef suppliers to supply a new supply of patties for distribution. Quarter Pounders are expected to be available in restaurants this week.

All 900 restaurants that receive onions from Taylor Farms Colorado Springs will continue to sell onion-free Quarter Pounders for now, a company spokesman said.

No other burgers or products on the McDonald’s menu were affected by the outbreak.

The the strain of E. coli in the outbreakcalled O157:H7, produces a powerful toxin that can damage the lining of the small intestine.

The the outbreak was first reported on Tuesdaywhen the Centers for Disease Control and Prevention announced it was investigating an E. coli outbreak linked to McDonald’s Quarter Pounders in several states, prompting the fast-food chain to stop using diced onions and quarter-pound beef patties pound in several states, the agency. said then.

The CDC said Tuesday that the first E. coli case linked to McDonald’s occurred on Sept. 27. Colorado state health officials notified the CDC of an unusual increase in the disease on Oct. 10, and the agency began investigating on Oct. 15, Matt Wise, chief of the CDC’s Epidemic Response and Prevention Branch, told NBC News.

CDC he zeroed in on the sliced ​​onion on Quarter Pounders through Wednesday. On Thursday, McDonald’s said the onions linked to the outbreak came from Taylor Farms.

On Wednesday, distributor US Foods said Taylor Farms recalled four raw onion products out of an abundance of caution due to “potential E. coli contamination.” The company urged its customers, including restaurants, to stop using and destroy the affected products as soon as possible.

It also prompted other Colorado restaurant chains, including Illegal Pete’s and Taco Bell, to stop using onions on their menus.

A spokesperson for Yum! Brands, the parent company of Taco Bell, said certain Pizza Hut and KFC locations have also removed fresh onions from their menus. There are no signs of E. coli illnesses linked to those restaurants.

The FDA said Thursday that it is looking into Taylor Farms as a possible source of the E. coli outbreak linked to Quarter Pounders, but added that “we are looking at all possible sources.”

A spokesman for Taylor Farms did not immediately respond to a request for comment Sunday.

As of Friday, 75 people in 13 states have been infected with the E. coli strain and one person has died, according to the CDC.

Twenty-two people were hospitalized and two people developed hemolytic uremic syndrome, a severe complication that can cause permanent kidney failure or death.

More people they sued McDonald’s claiming to have fallen ill after they ate at the restaurant.

This article was originally published on NBCNews.com