State ban comes on eve of major oyster festival.

WELLFLEET — State officials have closed all shellfish beds in Wellfleet because of an outbreak of suspected norovirus linked to consumption of shellfish from that area, according to the Department of Public Health.

This is not good news on the eve of one of the largest seafood festivals in the state, with Wellfleet’s OysterFest expecting 15,000 to 20,000 people this weekend.

Even though they take precautions to ensure the quality of the shellfish they serve, OysterFest organizers have decided not to serve raw shellfish during the weekend. The festival will go on with only cooked food and there will be a shucking contest with oysters from outside sources, they said.

"This is just one year of the 'Fest and what we care about most is running a safe and fun festival," said Michele Insley, executive director of the event-organizing Shellfish Promotion and Tasting, in a statement. "We also value the long-term sustainability of our town's second highest revenue producer, shellfishing, so we are erring on the side of caution."

In the past two days health officials have received reports of about 75 suspected cases of norovirus, primarily associated with eating raw shellfish at weddings and restaurants in the Outer Cape Cod area, the department notice says. Norovirus is known to exist in oysters and other shellfish and can cause severe gastrointestinal illness with stomach pain, vomiting and diarrhea. There is no cure, only treatment of symptoms.

Oysters are particularly good at transmitting the virus. A 2015 study examining DNA of the virus found that 80 percent of the strains found in humans were also found in oyster samples.

The Division of Marine Fisheries has notified the town and shellfish harvesters in the area about the closure, the notice says. The department's Food Protection Program is notifying businesses to recall any affected shellfish harvested on or after Sept. 26.

The affected areas are Wellfleet Harbor and Inner Harbor, Herring River and Loagy Bay, the notice says.

The state Tuesday had closed all waters in or adjacent to Nantucket Sound to shellfishing for most species as a precaution after it discovered a bloom of a species of phytoplankton that could produce a potentially deadly toxin. That closure expanded a previous closure of areas in Buzzards Bay and Mount Hope Bay. That toxin is unrelated to the norovirus.