One day after a multistate E. Coli outbreak linked to McDonald’s Quarter Pounder hamburgers was publicized, a major supplier of onions in that region has issued a recall.

Though federal regulators have not confirmed the source of the outbreak, which has so far killed one person and sickened 49, initial investigations have suggested that the fresh slivered onions served mainly atop the Quarter Pounder were a “likely source of contamination.”

Taylor Farms, the sole supplier of those onions to the affected McDonald’s locations in 10 states, issued a recall Wednesday of several yellow onion products because of “potential E. coli contamination,” according to a notice from U.S. Foods, which distributes the products to many restaurants.

The notice instructed restaurants to immediately stop serving the specified onions — diced, peeled and whole — and destroy them.

The items were voluntarily recalled by Taylor Farms Colorado out of an “abundance of caution,” a spokeswoman for U.S. Foods said in an email. Taylor Farms did not immediately respond to requests for comment.

McDonald’s and the Food and Drug Administration said preliminary reviews linked the outbreak to those slivered onions, but health officials and McDonald’s said they had not ruled out possible contamination of the quarter-pound beef patties used for the popular menu item. The Department of Agriculture and the Centers for Disease Control and Prevention are also investigating the source of the contamination.