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

Cesar Piña, chief supply chain officer for McDonald’s North America, said in a statement released Tuesday that an initial investigation into the outbreak suggests that “a subset of illnesses may be associated with onion slivers used in the Quarter Pounder and from a from a single supplier that supplies three distribution centers.”

Piña added that the fast food giant is pausing distribution of onion slivers in affected states and that inventory recovery notices are being distributed to restaurants in affected areas.