McDonald’s on Sunday ruled out beef patties as a source of the E.coli outbreak linked to Quarter Pounder hamburgers, which has killed at least one person and sickened nearly 75 others.

"We remain very confident that any contaminated product related to this outbreak has been removed from our supply chain and is out of all McDonald’s restaurants," the fast-food chain's Chief Supply Chain Officer Cesar Pina said in a statement.

The Colorado Department of Agriculture said that all subsamples from multiple lots of McDonald’s brand fresh and frozen beef patties had tested negative for E. coli, adding that it had completed beef testing and does not anticipate receiving further samples.

McDonald’s said it would resume distribution of fresh supplies of the Quarter Pounder and that it is expected to be available in all restaurants in the coming week, according to the statement.

Regulators had been investigating whether McDonald's beef patties could be affected.

The U.S. Food and Drug Administration and the U.S. Department of Agriculture didn't immediately respond to a Reuters request for comment.

E. coli is killed in beef when cooked properly. The McDonald's Quarter Pounder is served with raw, slivered onions; affected restaurants will serve the burgers without such onions.

U.S. fast-food chains have pulled fresh onions out of their menu items after the vegetable was named as the likely source of an E. coli outbreak.

McDonald's has pulled the Quarter Pounder from about one-fifth of its U.S. restaurants, including in Colorado, Kansas, Utah and Wyoming, and in parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma.

Past E. coli outbreaks have hampered sales at big fast-food restaurants as customers avoid affected chains.