“The decision to do this is not one we take lightly and was made in close consultation with the CDC,” McDonald’s U.S. President Joe Erlinger said in a video statement on Tuesday.

Cesar Piña, chief supply chain officer for McDonald’s North America, said in a statement Tuesday that an initial investigation into the outbreak indicated that “some of the illnesses may be related to chopped onions used in the Quarter Pounder that come from from a single supplier serving three distribution centers.”

Piña added that the fast food giant has halted the distribution of chopped onions in the affected states and that reports of restoring supplies have been spread to restaurants in the affected areas.