Risks of Eating Raw Oysters or Clams

Did You Know

Every year millions of Americans eat raw molluscan shellfish especially oysters and clams.

However, for some people, eating raw or undercooked oysters or clams can cause serious illness or even death from Vibrio vulnificus.

What Is It?

Vibrio vulnificus is a bacterium that can cause severe illness or death in some people who eat raw oysters or clams.

Between 1989 and 1996, the Centers for Disease Control and Prevention (CDC) reported 149 serious illnesses resulting in 75 deaths from Vibrio vulnificus infection.

Where Is it Found?

Vibrio vulnificus is found naturally in coastal waters. Vibrio vulnificus is NOT a result of pollution, and can be found in waters approved for oyster and clam harvesting. Vibrio vulnificus does NOT change the appearance, taste, or odor of oysters or clams.

Research shows that Vibrio vulnificus is found in oysters and clams from warm waters, such as the Gulf of Mexico. During the warm weather months of April though October, amounts of bacteria found in shellfish are higher.

How Can You Become Ill?

You can become ill by eating raw or undercooked oysters or clams. If the oysters or clams are cooked thoroughly, the Vibrio vulnificus bacteria are destroyed and there is no risk of infection.

Eating raw oysters or clams with hot sauce or while drinking alcohol does not destroy the bacteria. Infection can also occur when cuts, burn, or sores come in contact with seawater containing Vibrio vulnificus.

What Are the Symptoms?

Symptoms of Vibrio vulnificus include:

  • Vomiting
  • Diarrhea
  • Stomach pains
  • Severe weakness
  • Skin rashes and blisters
  • Shaking chills
  • High fever

It is important to remember that in "high risk" individuals Vibrio vulnificus infection can lead to death within two days. If you have any of these symptoms, see your physician immediately for medical treatment.

What Can You Do?

If you are at "high risk":

  • NEVER eat raw shellfish (oysters or clams)
  • ALWAYS choose cooked oysters or clams when dining out
  • ALWAYS cook oysters and clams thoroughly
  • NEVER swim or wade in saltwater with open wounds or sores

GET more information by calling the FDA hotline at 1-800-332-4010, your local or state health agencies, or your physician.

Who Is at Risk?

Most healthily individuals are not at risk from Vibrio vulnificus infections. Individuals with any of the conditions listed below are in a "high risk" category:

  • Liver disease
  • Alcoholism
  • Diabetes
  • AIDS or HIV infection
  • Gastric disorders
  • Inflammatory bowel disease
  • Cancer (including lymphoma, leukemia, Hodgkin's disease)
  • Hemochromatosis/hemosiderosis (abnormal iron metabolism)
  • Steroid dependency (as used for conditions such as emphysema, chronic obstructive pulmonary disease, etc.)
  • Any illness or medical treatment which results in a compromised immune system.
  • Older adults are more likely to have one or more of the above conditions and should be aware of their health status before eating raw oysters or clams.

Tips for Cooking Oysters & Clams in the Shell

  • Boil live oysters in boiling water for 3 to 5 minutes after shells open. 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.
  • Steam live oysters 4 to 9 minutes in a steamer that is already steaming.

Tips for Cooking Shucked Oysters & Clams

  • Boil or simmer for at least 3 minutes or until edge curl.
  • Fry in oil for at least 3 minutes at 375° F.
  • Broil 3 inches from heat for 3 minutes.
  • Bake for 10 minutes at 450°F.
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