OLYMPIA, Wash. -- Several people who ate raw oysters from the Samish Bay and Hood Canal areas got sick from a naturally-occurring bacteria called Vibrio parahaemolyticus. Cooking shellfish thoroughly prevents vibriosis illness and is especially important during the summer months when warm temperatures and low tides allow the bacteria to thrive.
State health officials close a shellfish growing area when there are four or more sporadic illnesses in a specific area; this recently happened in Samish Bay and in Hood Canal 5, which runs from Clark Creek (about a mile north of Hoodsport) north to Cummings Pointe.
Oyster harvest in both areas has been closed by the state Department of Health to reduce exposure to Vibrio bacteria. There have been other vibriosis cases identified this summer, scattered around the state's growing areas. Typically, Washington sees about 50 cases of vibriosis a year.
Vibrio parahaemolyticus bacteria are found naturally in the environment. When water temperature rises, so does the chance of dangerous bacterial growth. The warm weather and daytime low tides have likely contributed to the latest cases of illness.
Symptoms of vibriosis include diarrhea, abdominal cramps, nausea, vomiting, headache, fever, and chills. The symptoms usually appear about 12 hours after eating infected shellfish, but they can begin within two hours or as late as 48 hours after consumption. The illness is usually moderate and lasts for two to seven days; however, it can be more serious, even life threatening to people with weak immune systems or chronic liver disease. Taking certain medications may make vibriosis more likely to occur after eating shellfish.
To help keep shellfish safe to eat, keep them cool from the time they are harvested until the time they are cooked. Thorough cooking will kill the bacteria, making the shellfish safe to eat. Food safety specialists recommend oysters be cooked to an internal temperature of 145° F to kill the bacteria.
More information, including maps of the affected areas, is available on the agency's website.
It's important to remember that just because an area doesn't appear to be closed because of Vibrio parahaemolyticus, it may be closed for marine biotoxins. Check the biotoxin web page to make sure an area you wish to harvest in is free from marine biotoxins.