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 spokesperson said Sunday, citing tests by the Colorado Agriculture Department.

The department has no further plans to test the beef patties, the company spokesperson said, and the patties have been ruled out as the source of the outbreak.

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

McDonald’s stopped sourcing slivered onions from that source — Taylor Farms Colorado Springs — indefinitely on Sunday, the company spokesperson said, days after it removed the Taylor Farms onions from its supply chain.

The onions from Taylor Farms were sold in stores in Colorado, Kansas, Wyoming and parts of other states in the area, the spokesperson said. Some of those locations included airports, which could account for cases in other states.

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