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Cook Oysters Thoroughly

July 9, 2010

OLYMPIA (Department of Health) - Hot summer weather has finally arrived, just in time for some very low minus tides that will draw many people to Puget Sound beaches to harvest oysters. However, oysters harvested recreationally shouldn't be eaten raw because higher summer temperatures can warm the water where oysters live, leading to potential health risks.

Bacteria such as Vibrio parahaemolyticus are more likely to grow in warmer water. People who eat raw oysters harvested from warm water can get sick with an illness called vibriosis, caused by the naturally occurring bacteria. Cooking shellfish thoroughly will prevent illness and is always a good idea, especially during the summer when Vibrio parahaemolyticus is most active.

Multiple reports of vibriosis have led state health officials to issue a warning to recreational and commercial shellfish harvesters. Extra precautions have been put in place in the Hood Canal area because more than one illness has originated from oysters harvested there.

Vibriosis symptoms may include diarrhea, nausea, stomach cramps, headache, vomiting, fever, and chills ? that typically appear within 12 to 24 hours after infected shellfish is eaten. Typically, vibriosis is mild to moderate, with symptoms lasting for two to seven days. It can threaten the lives of people with lowered immunity or chronic liver disease.

If you do harvest oysters recreationally this summer, follow these steps to avoid vibriosis:

  • Put oysters on ice or refrigerate them as soon as possible after harvest.
  • If a receding tide has exposed oysters for a long time, don't harvest them.
  • Always cook oysters thoroughly. Cooking oysters at 145 F for 15 seconds destroys vibrio bacteria. Rinsing fully-cooked oysters with seawater can recontaminate them.

For commercial harvesters, special control measures are in place from May through September, to keep people from getting sick if they eat raw oysters. Shellfish companies must quickly refrigerate oysters after they're harvested. They're required to keep detailed harvest and temperature control records to show that the oysters were handled properly.

More information on shellfish safety is on the Department of Health Office of Shellfish and Water Protection's website (

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