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 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.

The FDA has issued an urgent recall for shellstock oysters harvested last month in Washington state's Hammersley Inlet.

According to a medical monthly report, 23 September to 6 October saw a huge rise in cases. At the time, Boots' Superintendent pharmacist Claire Nevinson issued a warning to parents. She said: "I always recommend encouraging your children to practice good personal hygiene, including regular hand washing with soap and warm water.