Oyster culture and harvest practices involve handling shellfish out of the water for varying time periods to reduce fouling and to harvest, cull or grade shellfish. During warm months, these practices can increase levels of pathogenic Vibrio parahaemolyticus populations in oysters and potentially increase the risk of illness for consumers. A more thorough understanding is needed of emerging aquaculture practices and appropriate management actions to reduce public health risks. Field-testing of Vibrio parahaemolyticus control measures for pre- and post-harvest husbandry practices have been conducted at harvest sites in Maine, New Hampshire, Massachusetts and Connecticut where aquaculture practices, regulations, environmental and seasonal climate conditions, and Vibrio parahaemolyticus populations all vary. The practices studied include exposure and re-submergence of both bottom and surface cultured oysters, relaying oysters, and temperature abuse (up to 12 h) of harvested oysters. Newly developed detection methods for regionally significant pathogenic Vibrio parahaemolyticus strains, i.e., ST36 and ST631, were used for evaluating Vibrio parahaemolyticus risk reduction.
Air exposure at elevated temperatures had inconsistent effects on the detection of pathogenic strains. Air exposed oysters at temperature equal to water temperatures caused much lower increased in Vibrio parahaemolyticus concentrations. Re-submergence trials in Maine, New Hamopshire and Massachusetts suggest 7 days is a consistently adequate time for re-submergence, while temperature abuse of harvested oysters for 5 hours or less did not significantly increase Vibrio parahaemolyticus concentrations. This study provides scientifically sound findings for each state and the region to use in managing the Vibrio parahaemolyticus risk in live shellfish to benefit the shellfish industry and consumer safety.