McDonald’s Corp. says Quarter Pounders will return to menus at all restaurants this week after ruling out beef patties as the source of a multistate E. coli outbreak that has sickened dozens and left one person dead.

The fast food chain said it combined its supply chain tracing data with information from government bodies, including an analysis by the Colorado Department of Agriculture that found no E. coli in dozens of samples from multiple lots of the restaurant’s fresh and frozen beef patties.

The E. coli infections have been linked to McDonald’s Quarter Pounders and appear to stem from the slivered onions served on top of the sandwich. The company had stopped selling the burgers in affected areas, and said on Sunday they will return without onions.

“The issue appears to be contained to a particular ingredient and geography, and 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 company said in a statement Sunday.

Colorado has reported the most illnesses in the outbreak, which is spread across 13 states, infecting 75 people and causing one death, the Centers for Disease Control and Prevention said on Friday.

The CDC said it believes the risk to the public is “very low,” citing actions taken by McDonald’s and the onion supplier, Taylor Farms, which has recalled several batches of the product.

Other fast-food chains have also pulled onions from their menus over E. coli concerns.