Hot Weather, Lowest Tides of the Year Raise Risk of Vibrio in Puget Sound Oysters

Get out and enjoy the low tides.

But be careful what you eat.

Saturday (June 24) and Sunday (June 25) will see tides 3.9 feet below average in south Puget Sound. Temperatures are forecast to be 90 and 93 degrees, respectively. The combination, however, leaves oysters out of water, exposed to the hot summer heat for so long that the naturally occurring bacterium Vibrio parahaemolyticus (Vp), filtered from the water by the oysters, grows at an accelerated rate inside of them. 

Historical outbreaks of vibriosis traced to oysters harvested from Washington state has already lead the Department of Health to issue its "vibrio advisory" warning for shellfish harvested from Hood Canal, Oakland Bay, Hammersley Inlet*, Totten Inlet, Eld Inlet, Pickering Passage, northern Case Inlet, North Bay and Burley Lagoon. It has also lead to more stringent rules surrounding harvesting, ranging from "time to ice" to complete closure of growing areas if water temperatures reach a certain level.

The Department of Health recommends you eat only well-cooked shellfish, especially in summer months, going further to say: "Do not consider shellfish to be fully cooked when the shells just open; they need to cook longer to reach 145° F." For additional information see the DOH website on vibriosis.

Get out and enjoy the low tides and warm weather this weekend. It won't get much better.

*Earlier in the year, oysters harvested from Hammersley Inlet were declared to be the source of norovirus, causing multiple illnesses and closure of commercial harvesting in the area. While the source has not been discovered, shellfish growers point to Shelton's waste water treatment facility which discharges directly into Hammerlsey Inlet and Oakland Bay. The City of Shelton denies its facility was the problem, claiming to have met all Department of Ecology standards.