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. Vibrio cholerae causes potentially severe diarrhea and does not occur naturally in the United States.
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Purpose of surveillance:
- To identify common source outbreaks
- To identify and eliminate sources of transmission including contaminated food and water
Forty-four laboratory-confirmed and two epidemiologically-linked cases of vibriosis were reported in 2013, which marks the highest number of annual reports to date. Two cases required hospitalization, and none died. Forty lab-confirmed cases were caused by V. parahaemolyticus, two were V. alginolyticus, one was V. fluvialis, and one was non-toxigenic V. cholerae. An additional eleven laboratory-confirmed cases were reported in non-King County residents whose most likely exposures were oysters consumed in King County.
Thirty-five (88%) of the forty Vibrio parahaemolyticus cases and the two epidemiologically-linked cases reported raw oyster consumption during their exposure period. Thirty cases purchased their oysters from King County commercial food establishments, four purchased outside King County (all oysters were from the Pacific Northwest), one case consumed oysters but did not know their source, and two cases consumed raw oysters harvested recreationally (Hood Canal and San Juan Islands areas). Two cases acquired infections to existing wounds after recreational exposure to Puget Sound waters north of King County. Of the remaining three cases, one became infected after consuming multiple types of non-oyster seafood while on vacation in the Caribbean, and for two cases a food history was not available.
International travel was the most likely source of exposure for the V. cholerae (Asia) and V. fluvialis (Mexico) cases, as well as one V. parahaemolyticus case (Caribbean) and one V. alginolyticus case (Mexico).
Over the last ten years in Washington state, between 18 and 80 cases have been reported, with the number varying depending on environmental conditions.