Purpose: This study determined the levels of total and pathogenic (tdh+ and/or trh+) Vp in shellfish harvested from Massachusetts, Connecticut, New York, and New Jersey and correlate those levels to water parameters.
Methods: Shellfish samples (oysters from all states and hard clams from CT and NY) were collected twice a month from May through September, 2014. Replicate shellfish samples were analyzed for each collection using a standard 3-tube MPN enrichment. Confirmation of total (tlh+) and pathogenic (tdh+ and/or trh+) Vpin enrichments was by real-time PCR.
Results: Of 112 shellfish samples, 109, 83, and 90 samples contained levels of total, tdh+, and trh+ Vp above the limit of detection (LOD; 0.03 MPN/g), respectively. In samples > LOD, mean levels were 1.5 log MPN/g (range: -1.44, 3.63), -0.46 log MPN/g (range: -1.82, 1.63), and -0.50 log MPN/g (range: -1.82, 1.63) for total, tdh+, and trh+ Vp, respectively. Mean water temperatures and salinities over the study were 20.4°C (range: 9.4 - 26.3) and 23.7 ppt (range: 10.1 - 30.0). Overall, there was a significant positive correlation between water temperature and total (r = 0.72, P < 0.001), tdh+ (r = 0.25, P < 0.01), and trh+ (r = 0.21, P < 0.05) Vp. A significant negative correlation was observed between salinity and total (r = -0.29, P = < 0.01) and tdh+ (r = -0.30, P = < 0.01) Vp, but not trh+ Vp.
Significance: As few illnesses were reported from these areas in 2014, these data provide valuable information on the baseline levels of total and pathogenic Vp that are generally not associated with illness. Additionally, the correlations with water parameters will allow refinement of the existing risk prediction model.