The Risk of Eating Raw Oysters or Clams
By Judith Wakefield
Clams and oysters harvested from approved waters, handled and processed in sanitary conditions, and properly refrigerated are safe for raw consumption by healthy individuals. Harvesting waters are monitored and if excessive levels of contaminants are found, commercial harvesting of shellfish is prohibited. Recreational fishermen should harvest clams or oysters only from waters that are safe and approved for harvesting.
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. Between 1989 and 1996, the Centers for Disease Control and Prevention (CDC ) reported 149 serious illnesses resulting in 75 deaths from Vibrio vulnificus infection.
Vibrio vulnificus is a bacterium that can cause severe illness or death in some people who eat raw oysters or clams. Vibrio vulnificus is found naturally in coastal waters and is NOT a result of pollution. It can even be found in waters approved for oyster and clam harvesting. Vibrio vulnificus does NOT change the appearance, taste, or odor of clams or oysters. During warm weather months of April through October, amounts of bacteria found in shellfish is higher. Oysters and clams are highly perishable and spoil quickly in the hot summer months if they are not properly refrigerated.
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. Infections can also occur when cuts, burns, or sores come in contact with seawater containing Vibrio vulnificus..
Most healthy individuals are not at risk from Vibrio vulnificus infections. But individuals with any of the following conditions are in a "high risk" category: Liver disease, Chronic alcohol abuse, Diabetes, AIDS or HIV infection, Gastric disorders, Inflammatory bowel or stomach disease, Cancer (including lymphoma, leukemia, Hodgkin’s disease, and especially if taking anti-cancer drugs or radiation treatment), Hemochromatosis/hemosiderosis (abnormal iron metabolism), Steroid dependency (as used for conditions such as emphysema, chronic obstructive pulmonary, etc.), Achlorhydria (a condition in which the normal acidity of the stomach is reduced or absent) or 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.
If you are at "high risk" what can you do? First, never eat raw shellfish - oysters, clams or even mussels. Always choose cooked shellfish when you are dining out. If you have them at home always cook them thoroughly. And just as important, never swim or wade in saltwater with open wounds or sores. You can get more information on this from the Food and Drug Administration hotline at 1-800-332-4010, the Health Department or your physician.
How do you know a good oyster when you see one? Oysters or clams in the shell (shellstock) should not gape and should close readily when tapped. However, soft-shell clams do not close completely because the neck of "siphon" often protrudes from the shell. Movement of the neck muscle should indicate the clam is alive. If an oyster shell doesn’t close tightly or the oyster or clam meat is dry when the shell is open, discard it. Avoid eating clams or oysters with broken or damaged shells.
Shellstock should be washed to remove excess debris prior to storage in well ventilated refrigerator container. Clams should be covered with a clean wet towel to prevent drying. The temperature of refrigeration units where oysters are stored should be between 34 degrees and 45 degrees. Shellfish should never be stored in air-tight containers and should be consumed as soon as possible. Shucked oysters or clams also require refrigeration, and be sure to eat them before the expiration date on the container. Raw and cooked oysters or clams should be handled separately to avoid possible cross contamination.
How do you cook oysters and clams in the shell? Use small pots to boil or steam them. Do not cook too many in the same pot because the ones in the middle may not get fully cooked. Steam live oysters or clams 4 to 9 minutes in a steamer that is already steaming. Cooking oysters and clams to an internal temperature of 140 degrees or greater for 4 to 6 minutes (or 3 to 5 minutes after the shell opens) destroys the common microorganisms of public health concern.
To cook shucked oysters and clams boil or simmer for at least 3 minutes or until the edges curl. Fry in oil for at least 3 minutes at 375 degrees. Broil 3 inches from the heat for 3 minutes. Or bake for 10 minutes at 450 degrees.
One of the advantages of living in a coastal county is the availability of shellfish. Some people like them raw, that’s fine if you are healthy. But people are taking their lives in their hands if they have one of the mentioned health problems that puts them in the "high risk" category and they still eat raw shellstock. For these people, eating thoroughly cooked shellfish is the safest way to enjoy them.