What is Vibrio vulnificus and where is it found?

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Vibrio vulnificus is a naturally occurring bacterium in warm coastal waters such as the Gulf of Mexico and South Atlantic Ocean. Concentration of V. vulnificus and cases of infection follow a seasonal trend, rising in April, peaking in August, and declining in November. V. vulnificus bacteria are not a result of pollution. Oysters feed by filtering water-surrounding areas where Vibrios may thrive and as a result, concentrate V. vulnificus in their tissues. When people with weak immune systems eat these shellfish raw or undercooked, the bacteria may enter their digestive tract and multiply rapidly. Additionally, individuals can become infected when open cuts, burns or sores come in contact with seawater containing V. vulnificus.

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​​​Why is Vibrio vulnificus of concern to public health officials?

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While not potentially life-threatening to most healthy people, symptoms of V. vulnificus infection may occur within 24 to 48 hours of ingestion. Symptoms may include sudden chills, fever, nausea, vomiting, diarrhea, shock and skin lesions. In people with certain medical conditions (i.e., cancer, diabetes, liver or stomach disorders, hemochromatosis, HIV/AIDS) death can occur within two days. According to the US Food and Drug Administration, “the risk of death is almost 200 times greater in those with liver disease than those without liver disease.” Anyone showing signs of any these symptoms after eating raw oysters should immediately seek medical attention. The fatality rate of high-risk individuals with V. vulnificus infections is 50 percent.

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Eating oysters from "clean" or approved waters or in reputable restaurants with high oyster turnover does not provide protection. Eating raw oysters with hot sauce or while drinking alcohol does not kill the bacteria, either. Only thorough heating can eliminate the bacteria. Post-harvest processes such as freezing, high-hydrostatic pressure, low-heat pasteurization, and irradiation can be used by the industry to reduce Vibrio bacteria to non-detectable levels of 30 MPN/gram.

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Why is Vibrio vulnificus important to oyster dealers (shellstock shipper, shucker-packer, repacker, reshipper, or depuration processor)?

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Raw oysters are the major source of food-borne disease caused by V. vulnificus. To minimize the risk of illness from the consumption of molluscan shellfish containing these pathogens, State Shellfish Control Authorities (SSCAs) place certain controls on the harvest of molluscan shellfish. Naturally occurring pathogens can be present in relatively low numbers at the time that molluscan shellfish are harvested, but may increase to more hazardous levels if they are exposed to time/temperature abuse.  In most cases, control for V. vulnificus involves limits on the time from harvest to refrigeration. The length of time is dependent upon the average monthly maximum water temperature (AMMWT) at the time of harvest, which is determined by the SSCA. For information about individual state Vibrio control plans, contact the SSCAs listed on the Interstate Shellfish Sanitation Conference website at www.issc.org.

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What is the processor’s and retailer's role in minimizing risk of Vibrio infections from raw oyster consumption?

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Shellfish Control Authorities require that shellstock intended for raw consumption bear a tag containing a warning about the risk of consuming raw or undercooked shellfish. The tag must remain on the bag until the shellfish is sold.  In addition, the tag or a record of the information it contains must be kept by the dealer for a minimum of 90 days. Because Vibrio bacteria increase when shellfish is temperature abused, dealers must ensure that it is received, stored, and shipped refrigerated at or below 45 ˚F (7.2 ˚C) or adequately iced. 

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Where can processors and dealers obtain additional information regarding handling and marketing of raw oysters to consumers and the required tags and records that are mandated by State Shellfish Control Authorities?

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Consult the most recent version of the “National Shellfish Sanitation Program Guide for the Control of Molluscan Shellfish,” as well as your state’s shellfish control authorities, a list of which can be found on the Interstate Shellfish Sanitation Program website at www.issc.org.

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What advisory information must the retailer provide to consumers of raw oysters?