Environmental investigations of Vibrio parahaemolyticus in oysters after outbreaks in Washington, Texas, and New York (1997 and 1998)

Total Vibrio parahaemolyticus densities and the occurrence of pathogenic st rains in shellfish were determined following outbreaks in Washington, Texas , and New York Recently developed nonradioactive DNA probes were utilized f or the first time for direct enumeration of V. parahaemolyticus in environm ental shellfish samples, V. parahaemolyticus was prevalent in oysters from Puget Sound, Wash.; Galveston Bay, Tex,; and Long Island Sound, N.Y., in th e weeks following shellfish-associated outbreaks linked to these areas. How ever, only two samples (one each from Washington and Texas) were found to h arbor total V. parahaemolyticus densities exceeding the level of concern of 10,000 g(-1). Pathogenic strains, defined as those hybridizing with tdh an d/or trh probes, were detected in a few samples, mostly Puget Sound oysters , and at low densities (usually <10 g(-1)). Intensive sampling in Galveston Bay demonstrated relatively constant water temperature (27.8 to 31.7<degre es>C) and V. parahaemolyticus levels (100 to 1,000 g(-1)) during the summer , Salinity varied from 14.9 to 29.3 ppt, A slight but significant (P < 0.05 ) negative correlation (-0.25) was observed between V. parahaemolyticus den sity and salinity. Based on our data, findings of more than 10,000 g-l tota l V. parahaemolyticus or >10 g(-1) tdh- and/or trh-positive V: parahaemolyt icus in environmental oysters should be considered extraordinary.