Variability of Total and PathogenicVibrio parahaemolyticusDensities in Northern Gulf of Mexico Water and Oysters

Vibrio parahaemolyticus is indigenous to coastal environments and a frequent cause of seafood-borne gastroenteritis in the United States, primarily due to raw-oyster consumption. Previous seasonal-cycle studies ofV. parahaemolyticus have identified water temperature as the strongest environmental predictor. Salinity has also been identified, although it is evident that its effect on annual variation is not as pronounced. The effects of other environmental factors, both with respect to the seasonal cycle and intraseasonal variation, are uncertain. This study investigated intraseasonal variations of densities of total and pathogenicV. parahaemolyticus organisms in oysters and overlying waters during the summer of 2004 at two sites in the northern Gulf of Mexico. Regression analyses indicated significant associations (P < 0.001) between totalV. parahaemolyticus densities and salinity, as well as turbidity in water and in oysters at the Mississippi site but not at the Alabama site. PathogenicV. parahaemolyticus organisms in Mississippi oyster and water samples were detected in 56% (9 out of 16) and 78% (43 out of 55) of samples, respectively. In contrast, 44% (7 out of 16) of oyster samples and 30% (14 out of 47) of water samples from Alabama were positive. At both sites, there was greater sample-to-sample variability in pathogenicV. parahaemolyticus densities than in totalV. parahaemolyticus densities. These data suggest that, although totalV. parahaemolyticus densities may be very informative, there is greater uncertainty when totalV. parahaemolyticus densities are used to predict the risk of infection by pathogenicV. parahaemolyticus than previously recognized.