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Oysters, a Simple Food with a Complicated History

With the New Orleans Saints playing in the Super Bowl and Fat Tuesday just days away, it’s quite likely that large amounts of raw oysters will be consumed over the next couple of days, maybe even the next couple of weeks, at various bars, restaurants, and parties.  What is less certain is the level of risk to those consumers created by their gulping down those delicacies.

First, the good news.  Oysters have been prized from the early days of civilization for their silky texture and taste of the sea. The cultivation of oysters began more than 2,000 years ago when Romans collected oyster seed stock near the mouth of the Adriatic Sea and transported them to another part of Italy for grow-out. The Romans had such a passion for oysters that they imported them from all over the Mediterranean and European coasts.  Also, raw oysters nutritionally consist of 23 percent carbohydrates, 33 percent fat and 44 percent protein. This makes them a balanced food and a good source of protein and Omega-3 fatty acids. Oysters are a good source of zinc, selenium, vitamin D, iron, magnesium and phosphorus. [1]

Perhaps of equal importance, raw oysters have always been linked with love. Aphrodite, the Greek goddess of love, sprang forth from the sea on an oyster shell, promptly gave birth to Eros, and the word “aphrodisiac” was born.  Casanova, the renowned 18th century lover, famously used to breakfast on 50 oysters.  This may not be simply myth.  A team of American and Italian researchers in 2005 analyzed bivalve mollusks – a group of shellfish that includes oysters – and found they were rich in rare amino acids that trigger increased levels of sex hormones.  The scientists stressed that the oysters have to be eaten raw to be most effective!

In contrast, raw oysters may contain a number of different harmful bacteria, and have been linked to serious illness and death.  As such, food safety experts and public health agencies have consistently warned of the serious potential risk created by these mollusks, when consumed uncooked.

The harmful bacterium most commonly associated with the consumption of raw oysters is Vibrio vulnificus.  It is a bacterium in the same family as those that cause cholera. It normally lives in warm seawater and is part of a group of Vibrios that are called “halophilic” because they require salt. V. vulnificus can cause disease in those who eat contaminated seafood or have an open wound that is exposed to seawater. It is found in all of the coastal waters of the United States. Environmental factors responsible for controlling members of V. vulnificus in seafood and in the environment include temperature, pH, salinity, and increased dissolved organics. [2]

V. vulnificus causes wound infections, gastroenteritis, or a syndrome known as “primary septicemia.”  Wound infections result either from contaminating an open wound with sea water harboring the organism, or by lacerating part of the body on coral, fish, etc., followed by contamination with the organism. The ingestion of V. vulnificus by healthy individuals can result in gastroenteritis.

Ingestion of the organism by individuals with some type of chronic underlying disease [such as diabetes, cirrhosis, leukemia, lung carcinoma, acquired immune deficiency syndrome (AIDS), AIDS- related complex (ARC), or asthma requiring the use of steroids] may cause the “primary septicemia” form of illness.  A recent study showed that people with these pre-existing medical conditions were 80 times more likely to develop V. vulnificus bloodstream infections than were healthy people.  In these individuals, the microorganism enters the blood stream, resulting in septic shock, rapidly followed by death in many cases; the mortality rate for individuals with this form of the disease is over 50%. [2]

Although oysters can be harvested legally only from waters free from fecal contamination, even legally harvested oysters can be contaminated with V. vulnificus because the bacterium is naturally present in marine environments. V. vulnificus does not alter the appearance, taste, or odor of oysters.

V. vulnificus is a rare cause of disease, and is likely underreported. Between 1988 and 2006, CDC received reports of more than 900 V. vulnificus infections from the Gulf Coast states, where most cases occur.  Before 2007, there was no national surveillance system for V. vulnificus, but CDC collaborated with the states of Alabama, Florida, Louisiana, Texas, and Mississippi to monitor the number of cases of V. vulnificus infection in the Gulf Coast region.  In 2007, infections caused by V. vulnificus and other Vibrio species became nationally notifiable. [3]

Another Vibrio pathogen often associated with raw oysters is Vibrio parahaemolyticus.   V. parahaemolyticus is a marine bacterium that occurs naturally in filter-feeding molluscan shellfish, like oysters. V. parahaemolyticus is also a bacterium in the same family as those that cause cholera. It lives in brackish saltwater and causes gastrointestinal illness in humans.   V. parahaemolyticus was first implicated in an outbreak of food poisoning in Japan, in 1950, and has been associated with sporadic cases and outbreaks (multiple cases) of illness in the United States since 1969.  An estimated 4500 cases of V. parahaemolyticus infection occur each year in the United States.

Most people become infected with V. parahaemolyticus bacteria by eating raw or undercooked shellfish, particularly oysters. Less commonly, this organism can cause an infection in the skin when an open wound is exposed to warm seawater. When ingested, V. parahaemolyticus causes watery diarrhea often with abdominal cramping, nausea, vomiting, fever, and chills. Usually these symptoms occur within 24 hours of ingestion. Illness is usually self-limited and lasts 3 days. Severe disease is rare and occurs more commonly in persons with weakened immune systems. [4]

Public health agencies have been consistently warning of these potential risks associated with the consumption of raw oysters. The U.S. Food and Drug Administration (FDA) has advised people with certain medical conditions not to eat raw oysters, and to only eat oysters that have been thoroughly cooked. In people with medical conditions such as cancer, diabetes, or liver disease death can occur within two days.  The FDA list of such medical conditions includes: 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.  [5]

People who drink alcoholic beverages (including beer and wine) regularly may be at risk for liver disease, and, as a result, may also be 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. [5]

In June of 2005, the FDA issued its “Letter to Health Professionals Regarding the Risk of Vibrio vulnificus Septicemia Associated with the Consumption of Raw Oysters”. The letter asked for the help of health professionals in alerting their patients in the at risk group about the threat of Vibrio vulnificus septicemia associated with the consumption of raw oysters. The FDA therefore advised that those persons at-risk for V. vulnificus septicemia should only eat oysters that have been fully cooked. [6]

In addition to the Vibrios, raw oysters may also contain
other harmful organisms.&nb
sp; In March 2007, the FDA issued an alert regarding an outbreak of norovirus-associated illness linked to eating raw oysters harvested from San Antonio Bay, TX.  Illnesses had been reported by 25 individuals who ate raw oysters at an event in Maryland. The Maryland Department of Health & Mental Hygiene’s test results from ill patients were positive for norovirus.  Symptoms of illness associated with norovirus include nausea, vomiting, diarrhea and stomach cramping. Affected individuals often experience low-grade fever, chills, headache, muscle aches and a general sense of tiredness within 48 hours of exposure to the virus.  The implicated oyster beds in San Antonio Bay were closed for some time, and the oyster distributors issued voluntary recalls of the product.  [7]

The FDA has consistently sought to dispel a number of common but wrong assumptions about the risks involved with the consumption of raw oysters.  These myths include: eating raw oysters is safe if you drown them in hot sauce, which kills everything; avoid oysters from polluted waters and you’ll be fine; an experienced oyster lover can tell a good oyster from a bad one; alcohol kills harmful bacteria; just a few oysters can’t hurt you; and avoid raw oysters in months without the letter “R” and you’ll be safe.  [5]

The 2005 FDA Food Code currently recognizes that food establishments may serve undercooked animal foods to a consumer upon his or her specific request, if the consumer is properly advised of the hazards associated with eating undercooked animal foods.  Many consumers and food establishments exercise this “consumer advisory” option with oysters. For oysters, the term “fully cooked” means that the product is allowed to reach an internal temperature of at least 145°F for 15 or more seconds.  The FDA Food Code contains additional recommendations for safe food handling practices in retail and foodservice operations.

The risk posed by raw oysters has also been addressed by various legislatures, which have typically mandated related warnings to potential consumers. For example, California  mandates a warning that contains the language ” THIS FACILITY OFFERS RAW OYSTERS FROM THE GULF OF MEXICO. EATING THESE OYSTERS MAY CAUSE SEVERE ILLNESS AND EVEN DEATH IN PERSONS WHO HAVE LIVER DISEASE (FOR EXAMPLE ALCOHOLIC CIRRHOSIS), CANCER OR OTHER CHRONIC ILLNESSES THAT WEAKEN THE IMMUNE SYSTEM.” See, 17 CCR 13675.  Florida requires a warning stating “Consumer Information: There is risk associated with consuming raw oysters. If you have chronic illness of the liver, stomach or blood or have immune disorders, you are at greater risk of serious illness from raw oysters, and should eat oysters fully cooked. If unsure of your risk, consult a physician.” See, 64D-3.040, F.A.C.    

Finally, the courts have also addressed the nature of risk posed by raw oysters, primarily in the context of personal injury claims, with somewhat inconsistent results. Louisiana’s highest court, for example, has held that the Vibrio vulnificus bacteria, which occurs naturally in the Gulf of Mexico, and is harmless to most people, does not render raw oysters containing the bacteria unreasonably dangerous. Thus, neither the distributor of oysters nor a restauranteur was liable where the plaintiff died after consuming raw oysters containing these bacteria. See, Simeon v. Doe, 618 So. 2d 848, 851 (La. 1993). A Kentucky court found that the presence of Vibrio bacteria in raw oysters did not constitute a manufacturing or design defect, because there are no reasonably available alternatives to bacteria-laced oysters, screening is not feasible, and bacterium poses little threat to healthy persons.  See, Edwards v. Hop Sin, Inc., 2003 Ky. App. LEXIS 213, at *4 (Aug. 29, 2003).  

In contrast, a Texas court found that there is no question Vibrio vulnificus bacteria are highly dangerous to people who suffer an immunosuppressed condition.  Therefore, the issue of whether raw oysters constitute a product that is “dangerous to an extent beyond that which would be contemplated by the ordinary consumer who purchases it, with the ordinary knowledge common to the community as to its characteristics”, could not be resolved as a matter of law, and needed to be determined by the trier of facts.  See, Ayala v. Bartolome, 940 S.W.2d 727 (1997). In Cain v. Sheraton Perimeter Park South Hotel, 592 So. 2d 218 (Ala.1991), a patron sued a hotel and its restaurant alleging that he contracted hepatitis from consuming raw oysters served by the restaurant.  The Supreme Court of Alabama held that a fact question was presented as to whether a patron should have reasonably expected that raw oysters may have been contaminated.

Most recently, during the fall of 2009, the issue of raw oyster safety was again raised, and publicly and heatedly debated. On October, 17, 2009, the FDA announced, at a meeting of shellfish regulators, the agency’s intention to reformulate its policy on processing raw oysters to reduce Vibrio vulnificus.  The FDA announced that it would change HACCP rules to require post-harvest processing to reduce the risk posed by the bacterium.  The new rule was intended to take effect by the beginning of risk season in 2011.  

“There’s just a very clear public health case,” said Michael Taylor, the top food safety official at the FDA. “Vibrio is one of the most horrific infections we know about. Fifteen people a year die from this. It’s excruciating. And the people who don’t die suffer life-changing injuries. But we can prevent this.” Federal officials, who are emphasizing food safety improvements, point to California as an example. Between 1991 and 2001, 40 people in California died of Vibrio infection.  In 2003, the state banned raw untreated oysters from the Gulf during warm months and fatalities dropped to zero, Taylor said.

Oystermen, state officials, and their representatives on Capitol Hill, however, quickly complained that the federal government was overreaching, and was likely to destroy a gastronomical delight and its related industry, setting off a flurry of political action.  Opponents of the proposed new rule argued that antibacterial processing, which is similar to pasteurization, would ruin the taste of raw oysters, triple their cost, and place excessive burdens on a business with over 3500 workers, and with deep cultural and culinary roots, that was already at risk.

The FDA reacted by temporarily shelving the proposed new rule.  On November 13, 2009, in a media release, the FDA announced “Since making its initial announcement, the FDA has heard from Gulf Coast oyster harvesters, state officials, and elected representatives from across the region about the feasibility of implementing post-harvest processing or other equivalent controls by the summer of 2011.  These are legitimate concerns.”  Accordingly, the FDA delayed the implementation of the rule, deciding instead that, prior to its proceeding, it would “conduct an independent study to assess how post-harvest processing or other equivalent controls can be feasibly implemented in the Gulf Coast in the fastest, safest and most economical way.”  [8]

So, pending possible future action by the FDA, consumers who choose to eat raw oysters should continue to be aware of the potential health hazards posed by these controversial mollusks. The Florida Department of Agriculture and Consumer Services provides the following tips on how to handle oysters safely:

BUYING, STORAGE AND HANDLING

Live Oysters:


  • Remember to purchase seafood last and keep it cold during the trip home.

  • Live oysters should close tightly when tapped. 

  • Discard any oysters that don’t close; this is an indication that the shellfish are dead.

  • They should have a mild odor, similar to the ocean.

  • Live oysters should be free of cracks

    .


  • They will remain alive for up to seven days in the refrigerator when stored at a constant 41 degrees F in a container with the lid slightly open. 

  • Drain excess liquid daily.



Shucked Oysters: 


  • Remember to purchase seafood last and keep it cold during the trip home.

  • Oysters have a fresh odor when freshly shucked.

  • A clear, slightly milky or gray liquid should surround freshly shucked oysters.

  • Freshly shucked scallops should have very little liquid in the package

  • Refrigerate shellfish in a sealed container on ice or in the coldest part of the refrigerator.

  • Store shucked oysters up to five days.

PREPARATION

  • Keep raw and cooked seafood separate to prevent bacterial cross-contamination.


  • After handling raw seafood thoroughly wash knives, cutting surfaces, sponges and your hands with hot soapy water.


  • Always marinate seafood in the refrigerator.


  • Discard marinade; it contains raw juices which may harbor bacteria.


  • When marinade is needed for basting reserve a portion before adding raw seafood.


COOKING

  • Wash live oysters thoroughly under cold running water prior to cooking.


  • Steamed or grilled: cook until shell opens.


  • Shucked oysters: bread and fry in oil for 3 to 4 minutes at 375 degrees F.


  • Shucked oysters: bake for 10 minutes at 450 degrees F.    [1]

REFERENCES:

[1]    “Oysters”, Foodreference.com;
[2]    Vibrio vulnificus, Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins Handbook, Centers for Disease Control and Prevention;
[3]    Vibrio vulnificus, General Information, Centers for Disease Control and Prevention;
[4]    Vibrio parahaemolyticus, General Information, Centers for Disease Control and Prevention;
[5]    Vibrio vulnificus Health Education Kit, U.S. Food and Drug Administration;
[6]    “Letter to Health Professionals Regarding the Risk of Vibrio vulnificus Septicemia Associated with the Consumption of Raw Oysters”, U.S. Food and Drug Administration, June, 2005;
[7]    “FDA Investigating Norovirus Outbreak Linked to Oysters”, FDA News Release, March 2, 2007;
[8]    “FDA Statement on Vibrio Vulnificus in Raw Oysters”, FDA News Release, Nov. 13, 2009.

© Food Safety News
  • Jerry

    A piece of advice to those who get sick: get a good attorney.

  • On the basis of this article, I’d be hesitant to go out for oysters anymore at all. But my understanding from previous reports and coverage by the folks at CSPI is that the vibrio concern is mostly isolated to Gulf Coast harvested oysters, and even more specifically to those harvested in this area from April to October. Is this wrong? Is vibrio something we need to worry about from New England and Pacific Northwest oysters as well?
    http://www.thefooddemocracy.blogspot.com

  • Kevin

    Patrick, “coverage by the folks at CSPI” didn’t tell you (and millions of others)
    that there are Vibrio vulnificus illnesses all along the Atlantic Coast – Chesapeake Bay,
    Long Island Sound, Delaware Bay, etc.
    And not just in oysters, from clams occasionally, too.
    (the bacteria also exists off Spain & Israel, too, plus Asia.
    Not as many Vv cases on the Atlantic Coast, to be sure.
    But CSPI leads people into thinking it is only with Gulf Oysters, and that’s wrong.

  • ericthered

    if you don’t know about eating oysters ask around.
    You will find that the smartest healthiest happiest people you know enjoy oysters on the half shell. The real men and women of this world make educated decisions, eat delicious foods, enjoy good sex, and live life without needing a nanny government to telling them what is good for them. Web articles and news headlines aren’t the right place to inform your self about what to eat, they are entertainment that makes money off making news.
    I wish good health to all.
    But, if you are already a sick or weak person there are probably a lot of things you shouldn’t do. Eating delicious oysters is just one of the things you will miss out on.

  • Alex Ortiz

    Thank you soo much to whoever wrote this info on ths pathogen, you guys really just helped me out on this project.

  • sick

    I been sick for 24 hrs. coming out both ends, never again will I eat a raw oyster, I’m
    69 eating them all my life, I done.