Oyster-related illnesses surge in Washington state

Jul 27, 2006 (CIDRAP News) – Washington state health officials said yesterday that 60 people have become ill after eating raw oysters from the state's coastal waters in recent weeks, well above the normal reported total for a whole year.

The Washington Department of Health (WDH) said it usually records about 20 cases of vibriosis a year, but a dramatic rise in cases prompted the state to close several oyster harvesting areas on Jul 20. The department closed more areas yesterday.

Two patients have been hospitalized in the outbreak, but there have been no deaths, a Washington health official told CIDRAP News today.

The vibrosis outbreak is the largest in 8 years, according to an article last week in Washington's Kitsap Sun newspaper.

Additional cases in Oregon and British Columbia have also been linked to eating raw Washington oysters. In a Jul 14 press release, the Oregon Department of Human Services said 14 people had become ill after eating raw oysters at restaurants around Portland.

New York City health officials, citing the outbreak in the Pacific Northwest, on Jul 21 issued a similar warning about eating undercooked shellfish after four clusters of vibriosis cases were recorded in the city.

Vibriosis is a bacterial illness caused by Vibrio parahaemolyticus, which naturally occurs in seawater. High levels can grow during summer. Nancy Napolilli, WDH director of food safety and shellfish, told the Kitsap Sun last week that unseasonably warm temperatures and afternoon low tides are likely causes of the dramatic rise in vibriosis cases. She also said a change in the strain of bacteria may also be a contributing factor.

Symptoms of vibriosis include diarrhea, abdominal cramps, nausea, vomiting, headache, fever and chills, the WDH said. They usually appear within 12 hours after eating infected shellfish, but can begin anytime between 2 to 48 hours after consumption. The illness is usually mild or moderate, lasting 2 to 7 days, but it can be life-threatening in people who have immune dysfunction or chronic liver disease. Most cases resolve without treatment.

Washington officials said that while the restricted oyster areas are closed to recreational harvesting, some commercial growers can continue harvesting oysters if they are shucked, packed, and labeled "for cooking only." Napolilli recommends that restaurants and consumers thoroughly cook all shellfish before serving or eating. Cooking shellfish to an internal temperature of 145°F kills the bacteria, she said.