Occurrence of Vibrio parahaemolyticus in two oregon oyster-growing bays

Occurrence of Vibrio parahaemolyticus in 2 Oregon oyster-growing areas (Yaquina and Tillamook Bays) was studied from November 2002 to October 2003. Vibrio parahaemolyticus was detected in 15.0% of oyster, 20.0% of seawater, and 47.5% of sediment samples with very low levels of pathogenic strains being detected in oysters (less than or equal to3.6 most probable number [MPN]/g). The densities of total and pathogenic V parahaemolyticus were higher in sediment (less than or equal to 1100 and less than or equal to43 MPN/g) than in seawater (less than or equal to15 and less than or equal to3.6 MPN/100 mL) or oyster (less than or equal to43 and less than or equal to3.6 MPN/ g). Densities of V. parahaemolyticus in both bays were positively correlated to water temperatures (P < 0.01), with higher densities in samples being detected in summer, especially July and August. There was no correlation between the densities of V. parahaemolyticus and water salinity or the densities of V. parahaemolyticus and bacterial populations in seawater. Freshly harvested oysters should be kept at refrigeration temperatures to prevent rapid growth of pathogenic V. parahaemolyticus in contaminated oysters.