Raw oysters are a delicacy among seafood diners worldwide. However, eating raw oysters may increase your risk for food poisoning and other health complications. While contamination of food from bacterial, viral or parasitic agents can happen at any time, primarily because of the transfer of harmful organisms from one surface to another, the risk is exacerbated for raw foods compared with cooked foods because there is no heat applied to kill the organisms.
Vibrio vulnificus Bacterial Infections
Raw oysters may cause food poisoning, particularly from Vibrio vulnificus, a bacterium that can spread through contaminated seawater and cause an onset of symptoms in healthy individuals between the first and seventh day of exposure. The FDA notes that exposure to Vibrio vulnificus can cause sudden chills, fever, nausea, vomiting and diarrhea within 24 to 48 hours; it can be potentially life-threatening to most people and lethal within two days if you have certain medical conditions such as diabetes, cancer or liver disease. You cannot tell whether a raw oyster is contaminated with Vibrio vulnificus by looking at it, smelling it, determining how fresh it is or the cleanliness of the waters where it was found, or by the reputation of the restaurant where you eat. Furthermore, adding lemon or lime juice or hot sauce does not kill the bacteria -- only heat does. Seek immediate medical attention if you suffer from symptoms after eating raw oysters.
Hepatitis A Virus Infections
Oysters may transmit hepatitis A virus infections to consumers who eat raw shellfish. Hepatitis A causes liver inflammation with flu-like symptoms. The virus is transmitted through food or water contaminated from a stool by an infected person or a food preparer who did not wash his or her hands after defecating. Research published in "Southeast Asian Journal of Tropical Medicine and Public Health" in 2010 identified the concurrent presence of hepatitis A virus and Escherichia coli in raw oysters collected in Thailand. Pathological strains of Escherichia coli can cause gastrointestinal infections and bloody diarrhea. The research concludes that these oysters are a heath risk for consumers. Onset of symptoms may take up to 28 days from exposure.
Norovirus Infections
Norovirus infection can cause severe diarrhea, vomiting and gastrointestinal illness, between 12 and 48 hours of exposure from raw oysters. Research published in the "Journal of Public Health" in 2010 presents an outbreak of intestinal inflammation among restaurant diners who ate oysters contaminated with norovirus. Oyster meat imported from Japan to Australia contaminated with norovirus involved 83 cases of illness, according to research published in "Clinical Infectious Diseases" in 2007.
Heavy Metal Toxicity
Raw oysters may contain heavy metals toxic to your liver and kidneys. Research published in "Bulletin of Environmental Contamination and Toxicology" in 2009 reports concentrations of lead, cadmium, copper and zinc in the soft tissue of oysters located in seven coastal lagoons of Northwestern Mexico were higher than values in polluted areas. The research warns that these oysters are a possible consumer health risk.
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