ABSTRACTVibrio parahaemolyticusandVibrio vulnificuscan grow rapidly in shellfish subjected to ambient air conditions, such as during intertidal exposure. In this study, levels of total and pathogenic (tdh+and/ortrh+)V. parahaemolyticusand totalV. vulnificuswere determined in oysters collected from two study locations where intertidal harvest practices are common. Samples were collected directly off intertidal flats, after exposure (ambient air [Washington State] or refrigerated [New Jersey]), and after reimmersion by natural tidal cycles. Samples were processed using a most-probable-number (MPN) real-time PCR method for total and pathogenicV. parahaemolyticusorV. vulnificus. In Washington State, the mean levels ofV. parahaemolyticusincreased 1.38 log MPN/g following intertidal exposure and dropped 1.41 log MPN/g after reimmersion for 1 day, but the levels were dependent upon the container type utilized. PathogenicV. parahaemolyticuslevels followed a similar trend. However,V. vulnificuslevels increased 0.10 log MPN/g during intertidal exposure in Washington but decreased by >1 log MPN/g after reimmersion. In New Jersey, initial levels of all vibrios studied were not significantly altered during the refrigerated sorting and containerizing process. However, there was an increase in levels after the first day of reimmersion by 0.79, 0.72, 0.92, and 0.71 log MPN/g for total,tdh+andtrh+V. parahaemolyticus, andV. vulnificus, respectively. The levels of all targets decreased to those similar to background after a second day of reimmersion. These data indicate that the intertidal harvest and handling practices for oysters that were studied in Washington and New Jersey do not increase the risk of illness fromV. parahaemolyticusorV. vulnificus.IMPORTANCEVibrio parahaemolyticusandVibrio vulnificusare the leading causes of seafood-associated infectious morbidity and mortality in the United States.Vibriospp. can grow rapidly in shellfish subjected to ambient air conditions, such as during periods of intertidal exposure. When oysters are submersed with the incoming tide, the vibrios can be purged. However, data on the rates of increase and purging during intertidal harvest are scarce, which limits the accuracy of risk assessments. The objective of this study was to help fill these data gaps by determining the levels of total and pathogenic (tdh+and/ortrh+)V. parahaemolyticusandV. vulnificusin oysters from two locations where intertidal harvest practices are common, using the current industry practices. The data generated provide insight into the responses ofVibriospp. to relevant practices of the industry and public health, which can be incorporated into risk management decisions.
A case-control analysis of traceback investigations for Vibrio parahaemolyticus infections (vibriosis) and pre-harvest environmental conditions in Washington State, 2013–2018