An outbreak of Vibrio parahaemolyticus in Washington state has sickened 22 people who ate raw oysters containing the bacteria.

So far, 18 cases of vibriosis have been linked to commercial shellfish operations and four illnesses to recreational oyster harvesting in Puget Sound and on the Washington coast, according to the Washington State Department of Health.

Vibrio parahaemolyticus is a naturally occurring bacteria. In the Pacific Northwest, it’s more likely to grow in July and August, when warm temperatures and low tides allow it to thrive.

It’s related to Vibrio vulnificus, which is prevalent in the warmer waters of the Gulf of Mexico.

Vibriosis symptoms typically appear within 12 to 24 hours after contaminated shellfish is eaten. Like most foodborne illnesses, it can be quite unpleasant — with diarrhea, nausea, stomach cramps, headache, vomiting, fever, and chills — but it usually abates within two to seven days. However, it can be life-threatening for people with lowered immunity or chronic liver disease.

Cooking shellfish thoroughly will prevent kill the bacteria, although that’s not always an appealing option to those who like to slurp raw oysters.

For commercial oyster harvesters in the Pacific Northwest, special control measures are in place from May through September to guard against Vibrio. 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.

The Washington State Health Department offers this advice for those who harvest oysters recreationally in the summer:

·         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.

·        Cooking oysters at 145° F for 15 seconds destroys Vibrio bacteria. Rinsing fully-cooked oysters with seawater can recontaminate them.