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Vibrio species are bacteria that occur naturally in marine waters. Eating undercooked or raw shellfish, especially raw oysters, is the main risk for acquiring vibriosis from infection with Vibrio parahaemolyticus. Growth of Vibrio species in seawater is amplified during the warm months and Vibrio levels in shellfish increase during the summer.

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Vibriosis in King County

Purpose of surveillance:

  • To identify common source outbreaks
  • To identify and eliminate sources of transmission including contaminated food and water

Vibriosis case data

Local epidemiology:

Thirty-two laboratory-confirmed cases of vibriosis were reported in 2015. This is fewer than the number reported in the past two years (34 cases in 2014, 46 in 2013), but slightly above the five-year average of 30 cases per year. One case required hospitalization, and none died. Twenty-three lab-confirmed cases were caused by V. parahaemolyticus, eight were caused by V. alginolyticus, and one was caused by non-toxigenic V. cholerae.

Twenty-one (91%) of the 23 Vibrio parahaemolyticus cases reported raw oyster consumption during their exposure period; the remaining two cases were lost to follow-up. Fifteen cases purchased their oysters from King County commercial food establishments, two from food establishments elsewhere in Washington, while three cases were exposed outside of Washington State. One Vibrio parahaemolyticus case was related to recreationally harvested oysters served at a private party.

Of the eight V. alginolyticus cases reported in 2015, six reported recreational water exposure (3 Mexico, 2 Hawaii, 1 Puget Sound), one reported a gastrointestinal illness potentially related to ceviche consumption in Las Vegas, and one was lost to follow up. Four cases reported a pre-existing abrasion at the site of infection.

The most likely exposure for the case of non-toxigenic V. cholerae was consumption of raw oysters in a Puget Sound restaurant. Non-toxigenic V. cholerae is occasionally detected in the Puget Sound during warmer summer months.

An additional seven laboratory-confirmed cases were reported in non-King County residents whose most likely exposures were oysters consumed in King County.

One major preventative measure taken this year toward improved shellfish safety was the implementation of an updated Washington State Vibrio parahaemolyticus (Vp) Control Plan. Led by the Washington State Office of Shellfish and Water Protection, this proposal revised the existing WAC to place more preemptive controls on shellfish harvesting during periods of warm water temperatures.

Over the last ten years in Washington state, between 20 and 90 cases have been reported, with the number varying depending on environmental conditions.