From gourmet delight to fatal mistake, eating raw oysters or clams can be a serious risk for consumers with certain medical conditions.
The problem is an infection caused by the bacterium, Vibrio vulnificus. Vibrio vulnificus is a bacterium that is native to southern U.S. coastal waters. The populations of this organism increase rapidly in warm weather, usually April to September. The bacteria accumulate in oysters and clams that grow in those waters.
Eating raw or undercooked oysters and clams can be a serious risk for people with liver disease, including hepatitis, cirrhosis, alcoholism, diabetes, cancer, leukemia, hemochromatosis, HIV/AIDS or any illness or medical treatment that weakens the immune system. Even consumers who have had gastric surgery or those who take prescribed medications to decrease stomach acid are also at risk for this infection.
Vibrio vulnificus can also cause an infection of the skin when open wounds are exposed to warm seawater. These infections may lead to skin breakdown and ulceration.
In these at-risk persons, the bacteria can infect the blood stream, causing a severe and life-threatening illness. Symptoms are fever and chills, decreased blood pressure or septic shock and blistering skin lesions. Vibrio ulnificus bloodstream infections are fatal about 50 percent of the time. Illness in at-risk individuals can progress very rapidly, possibly resulting in death within two days. It is important to seek medical attention immediately.
Among healthy people, ingestion of vibrio vulnificus can cause vomiting, diarrhea, and abdominal pain which is usually temporary and without complications.
Thorough cooking of oysters and clams kills the bacteria. To cook live oysters or clams in the shell, use small pots so shellfish in the middle is thoroughly cooked. Boil the shellfish for three to five minutes after the shells open or steam for four to nine minutes in a pot that contains boiling water.
To cook shucked oysters, those without shells, boil or simmer for at least three minutes or until edges curl or fry at 375 degrees F for at least three minutes; or broil three inches from heat for three minutes; or bake at 450 degrees F for 10 minutes.
Vibrio vulnificus is not a result of pollution and can be found in waters approved for shellfish harvesting. The molluscan shellfish industry and the Interstate Shellfish Sanitation Conference are researching and implementing ways to reduce this risk.
Thorough cooking is advised.