Vibrio parahaemolyticus, a gram-negative, halophilic bacterium that inhabits warm estuarine waters worldwide, is the most common cause of seafood-associated bacterial gastroenteritis in the United States. The most common vehicle for this infection in the United States is the consumption of raw or improperly cooked oysters. Before the summer of 2004, Alaskan waters were thought to be too cold to support levels of V. parahaemolyticus high enough to cause disease.
Thermostable direct hemolysin (encoded by tdh) is a virulence factor that occurs in more than 90 percent of clinical strains of V. parahaemolyticus but usually in less than 1 percent of environmental isolates.A single nonpathogenic strain of V. parahaemolyticus was reported from environmental culture in Alaska only once. From 1995 to 2003, the Alaska Department of Environmental Conservation (DEC) tested approximately 400 Alaskan oysters and other marine environmental samples for vibrio species; none yielded V. parahaemolyticus (DEC: unpublished data).