Vibrio vulnificus and Oysters

Isolated by the Centers for Disease Control in 1964 and formally documented in 1979,(1)Vibrio vulnificus is a gram-negative bacterium that occurs naturally in warm, unpolluted seawater. Vibrio vulnificusabundance is positively correlated with seawater temperature, and warmer water temperatures are linked to an increase in Vibrio vulnificus related illnesses, i.e., warmer summer months have a significantly higher number of Vibrio vulnificus related illnesses reported than do cooler winter months(2).

Transmission of Vibrio vulnificus to humans occurs through two methods: (1) the direct consumption of raw, undercooked or non-depurated seafood (finfish, crustaceans, and mollusks) and (2) exposure of wounds to contaminated seawater. Once an individual is infected, replication of the bacteria within tissues is rapid(3). Healthy individuals are at no serious risk of infection, but for a small number of individuals considered at-risk, Vibrio vulnificus infection can cause severe illness (primary septicemia and septic shock). Although Vibrio vulnificus related infections are treatable with a regimen of antibiotics and supportive care, without prompt medical attention the health of infected patients can deteriorate rapidly. The result of which can be a greater than 50% mortality rate(4).

Oysters are sedentary bivalve mollusks that feed by filtering plankton (small plants and animals) from estuarine water. Because Vibrio vulnificusoccurs naturally in the same waters that oysters feed, the bacteria is ingested and becomes assimilated and concentrated in the animal’s tissues. When people ingest oysters, there is a risk of also ingesting Vibrio vulnificus. The infection dose for Vibrio vulnificus is not accurately known. Healthy individuals can safely consume raw oysters without serious risk of Vibrio vulnificus illness. However, at-risk oyster consumers can eliminate their risk by eating oysters fully cooked or reduce their risk by eating oysters that have been post-harvest processed. Both of these techniques adequately reduce the Vibrio vulnificus bacteria. Although the number of illnesses that result from Vibrio vulnificus is extremely low when compared to other food-borne illnesses(6), primary source literature has repeatedly stressed the need for increased and continued educational programs targeting medical/health professionals and the at-riskpatient/oyster consumer.(7)