The US Food and Drug Administration began issuing warnings about a potential norovirus outbreak in oysters harvested from Washington state in early December

The Food and Drug Administration issued an oyster recall Thursday—it’s fourth in three weeks, after hundreds have been left sick—warning against the eating of certain oysters harvested in Washington that may be contaminated with the highly contagious norovirus.

Restaurants in Washington and Oregon purchased these oysters and they could have been distributed to other states. “The FDA is awaiting further information on distribution of these oysters and will continue to monitor the investigation and provide assistance to state authorities as needed,” the agency said.

The U.S. Food and Drug Administration is recalling oysters harvested from Puget Sound in December, citing possible norovirus contamination. It’s one of several recalls to impact the Pacific Northwest’s shellfish supply in the past month.