Global dissemination of Vibrio parahaemolyticus serotype O3:K6 and its serovariants.

Vibrio parahaemolyticus is recognized as a cause of food-borne gastroenteritis, particularly in the Far East, where raw seafood consumption is high. An unusual increase in admissions of V. parahaemolyticus cases was observed at the Infectious Diseases Hospital in Calcutta, a city in the northeastern part of India, beginning February 1996. Analysis of the strains revealed that a unique serotype, O3:K6, not previously isolated during the surveillance in Calcutta accounted for 50 to 80% of the infections in the following months. After this report, O3:K6 isolates identical to those isolated in Calcutta were reported from food-borne outbreaks and from sporadic cases in Bangladesh, Chile, France, Japan, Korea, Laos, Mozambique, Peru, Russia, Spain, Taiwan, Thailand, and the United States. Other serotypes, such as O4:K68, O1:K25, and O1:KUT (untypeable), that had molecular characteristics identical to that of the O3:K6 serotype were subsequently documented. These serotypes appeared to have diverged from the O3:K6 serotype by alteration of the O:K antigens and were defined as "serovariants" of the O3:K6 isolate. O3:K6 and its serovariants have now spread into Asia, America, Africa, and Europe. This review traces the genesis, virulence features, molecular characteristics, serotype variants, environmental occurrence, and global spread of this unique clone of V. parahaemolyticus.