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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Purpose of surveillance:
- To identify common source outbreaks
- To identify and eliminate sources of transmission including contaminated food and water
Thirty-four laboratory-confirmed cases of vibriosis were reported in 2014. This is fewer than the record number reported in 2013 (46 cases), but still above the five-year average of 27 cases per year. Three cases required hospitalization, and none died. Thirty-two lab-confirmed cases were caused by V. parahaemolyticus, one was V. alginolyticus, and one was non-toxigenic V. cholerae.
An additional nine laboratory-confirmed cases were reported in non-King County residents whose most likely exposures were oysters consumed in King County.
Twenty-eight (88%) of the 32 Vibrio parahaemolyticus cases reported raw oyster consumption during their exposure period. Seventeen cases purchased their oysters from King County commercial food establishments, four cases from food establishments elsewhere in Washington, while seven cases one in four were exposed outside of Washington State (3 British Columbia, 2 Oregon, 2 California). Two Vibrio parahaemolyticus cases were linked to seafood other than oysters: one case's most likely exposure was Dungeness crab recreationally harvested from Hood Canal in early July; another case's only exposure was cooked clams purchased at a King County restaurant. Public Health was unable to obtain exposure information from the remaining two cases.
The V. alginolyticus case was likely infected while swimming in Southeast Asia and subsequently developed an ear infection. Unlike infections from V. parahaemolyticus or V. cholerae, V. algynolyticus infections are most often acquired by swimming or wading in sea water (including the Puget Sound). Cases usually have a pre-existing open wound (such as an ear infection or cut on the foot) which becomes infected by the bacteria.
Over the last ten years in Washington state, between 20 and 90 cases have been reported, with the number varying depending on environmental conditions.