Norovirus impacts an oyster festival in Cape Cod – NoroCORE Food Virology

Norovirus impacts an oyster festival in Cape Cod

photo of oysters on the half shell

What do you do when well-laid plans go awry because of norovirus? If you are the Wellfleet OysterFest, you turn those lemon wedges meant to go with your raw oysters into lemonade. (We mean figuratively of course, we don’t know that they actually did that, but they did to a good job of making the best of a tricky public health situation.)

Just two days before the 16th Annual Wellfleet Oysterfest, approximately 75 people in the area developed norovirus-like illness. Most of the cases were associated with eating raw shellfish at weddings and restaurants in the outer Cape Cod area, and stool samples from some of these individuals tested positive for the virus.

As a result, the shellfish beds in Wellfleet were immediately closed for 21 days by Massachusetts state health officials starting on October 13, and product from Wellfleet Harbor, Wellfleet Inner Harbor, Herring River, and Loagy Bay harvested on or after September 26 was recalled. This recall included oysters, hard-shell clams, soft-shell clams, mussels, and razor clams.

In response, the festival organizers made some quick alterations to ensure the safety of their tens of thousands of attendees, in a two-day bash where hundreds of thousands of oysters and other shellfish are typically consumed. The festival went on with its regularly-scheduled events and was generally well-attended, but without any raw oysters on the menu. Instead, they served a variety of cooked oyster dishes and held their “shuck off” competition using oysters from other areas.

 

So how does norovirus get into molluscan shellfish?

Norovirus only infects humans, and when we are infected with the virus we shed millions to billions of copies of it in our stool and vomit. Since that is the only source of the virus, when molluscan shellfish (such as oysters, clams, and mussels) come into contact with the virus it generally means these animals were living in an environment contaminated for a time with human waste. By an interesting fact of their biology (that is very convenient for the virus), these animals can actually concentrate these viruses in their gut tissues, potentially transferring norovirus to us when we eat oysters and other molluscan shellfish. It is most problematic when these items are eaten raw or only lightly cooked, and part of the reason you see those warnings on restaurant menus about consuming raw or undercooked shellfish.

There is significant product tracking for harvested shellfish in the US, and when a batch is strongly believed or confirmed to be contaminated with norovirus, the usual recourse is to temporarily close the harvesting areas these animals came from and initiate a recall of the affected product, as was done here. In the grand scheme of foodborne norovirus outbreaks, outbreaks related to contaminated oysters are actually quite uncommon.

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