McDonald’s has temporarily pulled the Quarter Pounder from restaurants in Colorado, Kansas, Utah and Wyoming, in addition to portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma. Photo: Mike Stewart/Associated Press

One person from Colorado has died and dozens of others have been sickened in 10 states, the Centers for Disease Control and Prevention said. The agency said the first illness was reported in September.

What was the cause of the outbreak at McDonald’s?

McDonald’s said that a subset of illnesses may be linked to slivered onions used in the Quarter Pounder and that the onions are sourced from a single supplier that served three distribution centers.

Colorado health officials said the Food and Drug Administration’s early read was that onions were the outbreak’s source, and that the slivered onions are used primarily on Quarter Pounders and not other McDonald’s menu items. The Agriculture Department is also looking into the burgers’ beef patties, state officials said.

The company didn’t name the supplier and said it paused distribution of slivered onions to stores in certain areas. Local restaurants were told to remove the product from their supply.

McDonald’s has temporarily pulled the Quarter Pounder from restaurants in Colorado, Kansas, Utah and Wyoming, in addition to portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico and Oklahoma.