Raw Oysters Contaminated With Vibrio vulnificus Can Cause Illness and Death

Understanding the Risks

Each year millions of Americans enjoy eating raw oysters. However, some people with certain medical conditions are at high risk for becoming seriously ill and dying from eating raw oysters. The U.S. Food and Drug Administration (FDA) is advising these high-risk individuals not to eat raw oysters, and to only eat oysters that have been thoroughly cooked.

The Cause: Vibrio vulnificus

Vibrio vulnificus (V. vulnificus) is a bacterium that occurs naturally in warm coastal areas, such as the Gulf of Mexico. Vibrio vulnificus is found in higher concentrations in the summer months as water becomes warmer.

Oysters feed by filtering water-surrounding areas where vibrios may thrive and as a result concentrate V. vulnificus in their tissues. When a person eats these shellfish raw or undercooked, the bacteria enter the digestive tract and multiply rapidly. In addition to ingestion, high-risk individuals can become infected when cuts, burns or sores come in contact with seawater containing V. vulnificus.

The Risk Factors

While not potentially life-threatening to most healthy people, symptoms of V. vulnificus infection may occur within 24 to 48 hours of ingestion and may include sudden chills, fever, nausea, vomiting, diarrhea, shock and skin lesions. In people with certain medical conditions such as cancer, diabetes or liver disease death can occur within two days. Anyone showing signs of any these symptoms after eating raw oysters should seek medical attention immediately.

Certain health conditions put people at high risk for serious illness or death from V. vulnificus infections. Some of these health conditions may be present without any symptoms so people may not know they are at risk. Individuals should check with their doctors if they are unsure of their risk. Vibrio vulnificus infections in high-risk individuals have a 50 percent fatality rate.

These conditions include:

• Liver disease (from hepatitis, cirrhosis, alcoholism, or cancer)
• Iron overload disease (hemochromatosis)
• Diabetes
• Cancer (including lymphomas, leukemia, Hodgkin's disease)
• Stomach disorders
• Or any illness or medical treatment that weakens the body's immune system, including HIV infection

Drinking Alcoholic Beverages Regularly and Liver Disease

People who drink alcoholic beverages (including beer and wine) regularly may be at risk for liver disease, and, as a result, at risk for serious illness or death from consuming raw oysters. Even drinking two to three drinks daily can contribute to the development of liver disease, which may occur without symptoms. Alcoholism and infections from Hepatitis can injure the liver and impair its function years before an individual begins to experience symptoms. Liver disease puts people at risk for V. vulnificus infection from raw oysters. The risk of death is almost 200 times greater in those with liver disease than those without liver disease.

Reducing Risk

Vibrio vulnificus bacteria are not a result of pollution, so although oysters should always be obtained from reputable sources, eating oysters from "clean" waters or in reputable restaurants with high turnover does not provide protection. Eating raw oysters with hot sauce or while drinking alcohol does not kill the bacteria, either. Only heat can destroy the bacteria.

Since thoroughly cooking oysters will destroy the bacteria, oysters can continue to be enjoyed in many cooked preparations by following this advice.

 COOKING OYSTERS

The presence of Vibrio vulnificus bacteria is not a result of pollution, so although oysters should always be obtained from reputable sources, eating oysters from "clean" waters or in restaurants with high turnover does not provide protection. Eating raw oysters with hot sauce or while drinking alcohol does not kill the bacteria, either. Only heat can destroy the bacteria.

Since thoroughly cooking oysters will destroy the bacteria, oysters can continue to be enjoyed in many cooked preparations by following this advice.

At Restaurants:

• Order oysters fully cooked.

Cooking at Home:

• When you purchase oysters the shells should be closed. Throw away any oysters with shells already opened.
• In the shell: After the shells open, boil live oysters for another 3-5 minutes. (Use small pots to boil or steam oysters. Do not cook too many oysters in the same pot because the ones in the middle may not get fully cooked. Discard any oysters that do not open during cooking).
• In a steamer: Add oysters to water that is already steaming and cook live oysters for another 4-9 minutes.

Shucked Oysters:

• Boil or simmer shucked oysters for at least 3 minutes or until the edges curl.
• Fry at 375 degrees for at least 3 minutes.
• Broil 3 inches from heat for 3 minutes.
• Bake at 450 degrees for 10 minutes.

For further information contact:
FDA Food Safety Hotline (English only) 1-888-SAFEFOOD