Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not all oysters are in the superfamily Ostreoidea.

Some types of oysters are commonly consumed cooked or raw, and in some locales are regarded as a delicacy. Some types of pearl oysters are harvested for the pearl produced within the mantle. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects.

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 United States 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.

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.

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

Ingredients

Serves 4

16 each - oysters - shucked
1/4 cup - olive oil
1 each - chopped, small onion
1 tablespoon - chopped, garlic
1 each - chopped, jalapeño chili
1 cup - chopped mushrooms
2 cups - chopped, spinach
1/4 cup - whipping cream or milk
1/4 cup - shredded cotija cheese

Preparation

1. Purchase oysters from a reputable vendor. Make sure they are completely closed shut. If an oyster shell is open discard.
2. Clean oysters thoroughly with water and scrub them with a brush so they are free of sand or dirt.
3. Shuck the oysters with a knife and rinse oyster thoroughly with water to clean any sand or dirt.
4. Clean oyster shells and arrange on a baking pan, set aside.
5. In a sauté pan add the oil and cook onions, garlic, and jalapeño peppers for 2 minutes.
6. Add mushrooms, and spinach and cook for 5 minutes or until ingredients are very soft and tender.
7. Season with salt and pepper.
8. Add the cream or milk and reduce slightly.
9. Add the cheese and combine thoroughly. Let mixture cool slightly.
10. Using a spoon, place a very thin layer of the mushroom and spinach mixture in the oyster shells, top with an oyster, then another layer of the spinach and mushroom mixture until you have two layers completed.
11. Sprinkle with cotija cheese and bake at 400 degrees for 10 to 15 minutes or until oysters are light brown and reaches the temperature of 180 degrees.
12. Serve hot and garnish with a lemon wedge.

Ingredients

Serves 4

16 each - oysters, shucked
2 cups - vegetables
Salt and pepper to taste

For the batter:
½ cup - flour plus ¼ cup for dusting
½ teaspoon - baking powder
¼ teaspoon - cayenne pepper
¼ teaspoon - black pepper
¼ teaspoon - salt

For the dipping sauce:
½ cup - mayonnaise
2 tablespoons - lemon juice
1 tablespoon - tapatio sauce

Preparation

1. Purchase oysters from a reputable vendor. Make sure they are completely closed shut. If an oyster shell is open discard.
2. Clean oysters thoroughly with water and scrub them with a brush so they are free of sand or dirt.
3. Shuck the oysters with a knife and rinse oyster thoroughly with water to clean any sand or dirt.
4. Season oysters with ¼ cup of flour seasoned with salt and pepper. Dust the oysters in the flour mixture and refrigerate until ready to use.
5. For the batter mix ½ cup of flour, the baking powder, cayenne pepper, black pepper and salt in a medium bowl. Gradually add the water to the dry mixture to form the batter.
6. In a two-quart saucepan add the oil and bring to a medium heat.
7. Dip the dusted oysters into the batter and slowly fry them in the hot oil for 3 minutes or until golden brown and the internal temperature reaches 180 degrees.
8. Place the fried oysters on a plate lined with paper towels so it absorbs the excess oil. Keep the oysters hot.
9. For the dipping sauce, add all ingredients in a small bowl and whisk until well combined.
10. Arrange 4 fried oysters per plate with some of the dipping sauce. Serve hot.

Ingredients

Serves 4

16 each - oysters, shucked
1/4 cup - olive oil
1 each - chopped, small onion
1 tablespoon - minced, garlic
2 each - chopped, ribs of celery
1 each - chopped, carrot
2 each - chopped, potatoes
1 quart - water
1 each - 8 oz. can tomato sauce (salsa de el pato)
1 each - chopped, tomato
Salt and pepper to taste

Preparation

1. Purchase oysters from a reputable vendor. Make sure they are completely closed shut. If an oyster shell is open discard.
2. Clean oysters thoroughly with water and scrub them with a brush so they are free of sand or dirt.
3. Shuck the oysters with a knife and rinse oyster thoroughly with water to clean any sand or dirt.
4. Using a one-gallon soup pot, bring oil to the smoking point.
5. Add the onions and garlic and cook for 2 minutes.
6. Add celery, carrots, and potatoes and continue to cook for 2 more minutes. Stir constantly so the vegetables are infused with flavor, not browned.
7. Add the water and the tomato sauce and bring to a boil.
8. Add the shucked oysters, season with salt and pepper and simmer until vegetables become fork tender, 10 to 15 minutes.
9. Ladle hot soup into 4 bowls and serve hot.

GARNISH: Fried tortilla chips or chopped cilantro and a wedge of lemon.

Before cooking, throw out any shellfish with open shells.

For shellfish in the shell, either:

• Boil until the shells open and continue boiling another 3–5 minutes; or
• Add to a steamer when water is already steaming and cook for another 4–9 minutes.

Only eat shellfish that open during cooking. Throw out any shellfish that do not open fully after cooking.

For shucked oysters, either:

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

Raw oysters contaminated with Vibrio vulnificus can be life threatening, even fatal when eaten by someone with liver disease, diabetes or a weakened immune system. However, there are myths that encourage people to eat raw oysters in spite of these dangers. Some of these myths, and the true facts behind them, include:

MYTH:Eating raw oysters are safe if you drown them in hot sauce, which kills everything.

Fact: The active ingredients in hot sauce have no more effect on harmful bacteria than plain water. Nothing but prolonged exposure to heat at a high enough temperature will kill bacteria.

MYTH:Avoid oysters from polluted waters and you'll be fine.

Fact:Vibrio vulnificus in oysters has nothing to do with pollution. Rather these bacteria thrive naturally in warm coastal areas (such as the Gulf of Mexico) where oysters live.

MYTH:An experienced oyster lover can tell a good oyster from a bad one.

Fact:Vibrio vulnificus can't be seen, smelled, or even tasted. Don't rely on your senses to determine if an oyster is safe.

MYTH:Alcohol kills harmful bacteria.

Fact: Alcohol may impair your good judgment, but it doesn't destroy harmful bacteria.

MYTH:Just a few oysters can't hurt you.

Fact: Roberta Hammond, Ph.D, the Food and Waterborne Disease Coordinator for Florida, cites a case where a fatality caused by Vibrio vulnificus occurred after eating only three oysters. The seriousness of any case depends on many factors, including how much bacteria is ingested and the person's underlying health conditions.

MYTH:Avoid raw oysters in months without the letter "R" and you'll be safe.

Fact: While presence of Vibrio vulnificus bacteria is higher in warmer months, according to the Department of Health and Human Service's Centers for Disease Control and Prevention (CDC), a full 40 percent of cases occur during colder months from September through April.

MYTH:Raw oysters are an aphrodisiac and will cure a hangover.

Fact: There is no scientific evidence that either of these commonly held beliefs is true.