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There’s Risk in Eating Raw Oysters

Each year millions of Americans enjoy raw oysters with a squeeze of lemon or perhaps a dash of hot sauce.  However, when eaten raw, this tasty mollusk poses certain health risks.

Last month, the Florida Department of Health issued a press release warning residents with certain health conditions to avoid eating raw oysters and exposing open wounds to seawater and estuarine due to the potential exposure to Vibrio vulnificus bacteria.

Vibrio vulnificus is a naturally occurring bacterium found in marine waters, particularly those waters with low salinity levels such as bays and estuaries. The bacterial population is typically greatest during the summer months when water temperatures rise.

In Florida, the bacteria are a major concern since Vibrio vulnificus occurs naturally in the warm waters of the Gulf coast from May through November. According to an article in the American Family Physician, “although it is found in all coastal waters of the United States, most V. vulnificus infections are attributed to consuming raw oysters harvested in the Gulf of Mexico during the summer.”

Because oysters are filter feeders, meaning they filter water containing plankton and food particles through gills, it is common for Vibrio vulnificus to become concentrated in their tissues when feeding in waters where bacteria thrive.

Raw oysters have also been associated with norovirus, including a recent outbreak in Canada’s British Columbia.

On a list of common myths about raw oysters, FDA explains that even an experienced oyster lover cannot tell a good oyster from a bad one.  There is no change to the taste, odor, or appearance of seafood contaminated by Vibrio vulnificus, which creates a significant challenge for food safety officials and consumers who cannot rely on their senses to determine if an oyster is safe.

In addition, Vibrio vulnificus bacteria are not a result of pollution.  This creates another challenge in that eating oysters from “clean” waters or in restaurants with high turnover will not guarantee that it is free of harmful bacteria.

Florida Department of Health officials as well as FDA and CDC caution that only heat can destroy the bacteria and make it safe for consumption.  Those agencies recommend that people, especially those individuals who are at the highest risk for infection, consume oysters that are thoroughly cooked by frying, stewing, or roasting.

According to an FDA fact sheet, people with certain health conditions, including individuals with liver damage or disease, diabetes, cancer, stomach disorders or any illness or treatment that weakens the immune system, are most at risk for developing serious illness from the bacteria.  FDA points out that although healthy people may also develop a bacterial infection from eating raw oysters, their illness tends to be less severe than those with preexisting health conditions.

While Vibrio vulnificus is not typically a life-threatening bacteria, individuals exposed to it may display various symptoms including nausea, vomiting, abdominal pain, diarrhea, fever, chills, and the formation of blistering skin lesions.

Aside from instructing consumers to cook oysters to ensure safety, Florida has taken steps to reduce the rate of Vibrio illness under the auspices of the National Shellfish Sanitation Program.  The program, passed by the Interstate Shellfish Sanitation Conference requires Florida, as well as other Gulf states including Texas, Mississippi, Alabama and Louisiana,  to implement a Vibrio vulnificus Risk Management Plan.

Under the National Shellfish Sanitation Program, the Risk Management Plan must include a consumer education program, a standardized process to collect information for each Vibrio illness, a process to track products implicated in Vibrio illnesses, and a plan to implement any additional controls in order to reduce the rate of illness by 60 percent.

Currently, the actual illness reduction rate achieved was determined by the Interstate Shellfish Sanitation Conference to be 35.2 percent.  This year, Florida and other Gulf states have implemented what they predict to be the necessary controls to achieve the additional 24.8 percent illness rate reduction to meet the 60 percent reduction goal.

However, it should be noted that Vibrio vulnificus is one of the few foodborne illnesses that has been shown to have an increasing rate of incidence. According to data from the CDC, the average annual incidence of Vibrio vulnificus infections increased by 41 percent between 1996 and 2005.

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