BALTIMORE, MD (August 11, 2010) - The Maryland Departments of Health and Mental Hygiene (DHMH) and of the Environment (MDE) are reminding consumers of the potential risk of eating uncooked oysters, clams, mussels and other shellfish during the warmer months of the year. The yearly increase in Vibrio bacteria as the water temperature warms, is found naturally in coastal waters such as the Chesapeake Bay and its tributaries. The bacteria can also pose a threat of infection to persons with open cuts, scrapes, burns or sores who are exposed to coastal waters.
"We’ve seen recent infections associated with swimming or working in brackish bay waters and Maryland’s water temperatures have been higher than normal this summer," says Frances Phillips, DHMH Deputy Secretary of Public Health Services. "While we want everyone to enjoy fresh Maryland seafood this summer, we also want people to be aware of how to protect themselves from illness and infection."
Shellfish, which are filter-feeding organisms, are bivalve mollusks such as clams, oysters, and mussels. The term shellfish does not include crabs, lobsters, or shrimp.
To date, 24 cases of Vibrio infection have been reported in Maryland; on average approximately 30 cases are reported each year. Depending on manner of exposure, Vibrio bacteria can cause several types of illness ranging from wound infections to serious gastrointestinal disease. Serious complications are more likely to occur in high risk individuals with the following conditions:
- Liver disease (from hepatitis, cirrhosis, alcoholism)
- Diabetes
- Cancer (including lymphomas, leukemia, Hodgkin's disease)
- People taking certain medications, such as stomach acid reducers
- Iron overload disease (hemochromatosis)
- Any illness or medical treatment that weakens the body's immune system
"It is recommended that high risk people avoid consumption of raw shellfish," said Dr. David Blythe, DHMH State Epidemiologist. "All Marylanders should be aware that Vibrio bacteria can potentially cause illness in people who eat raw or undercooked oysters or clams, regardless of age or health history."
Symptoms of illness from ingesting Vibrio bacteria can include vomiting, diarrhea, stomach pains, severe weakness, skin rashes, blisters, shaking chills and high fever. If you have any of these symptoms after consuming shellfish, see your health care provider for medical treatment.
Cooking Shellfish
Shellfish should be cooked thoroughly to avoid health risks from Vibrio bacteria. Vibrio bacteria do not change the appearance, taste, or odor of oysters or clams. Only thoroughly cooking the oysters or clams will destroy the bacteria and eliminate the risk of infection:
- Live oysters or clams should be boiled three to five minutes after their shells open.
- Using a small pot to boil or steam oysters is recommended for thorough cooking.
- Discard any oysters that do not open during cooking.
- Shucked oysters or clams should be boiled or simmered at least three minutes or until the edges curl.
- They may also be fried in oil for three minutes at 375 degrees, broiled three inches from the heat for three minutes or baked in a 450 degree oven for 10 minutes.
Eating raw oysters or clams with hot sauce or while drinking alcohol does not destroy the bacteria. Anyone who works or swims in or catches any seafood from brackish bay waters or streams and rivers should thoroughly wash hands before cooking or eating.
Avoiding Infection
The only way to prevent infection is to avoid contact with the water. When water contact through swimming, working, or fishing cannot be avoided:
- Cover wounds with water proof bandage
- Carry hand sanitizer so that wounds that occur during water contact can be cleansed immediately
- Wash hands before handling food or eating
- Always shower following contact with natural waters
- Wear water shoes while wading to avoid cutting your feet
If anyone in contact with brackish bay waters or tributaries experiences signs of skin infection, such as redness or swelling, they should promptly see a doctor or health care provider.
Maryland Department of the Environment Science Services Director Rich Eskin said: "Vibrio are naturally occurring in the Chesapeake Bay and are not necessarily related to specific pollution sources. The primary environmental factors controlling vibrio frequency are temperature and salinity, and recent research has suggested that nutrients may play a role in vibrio concentration."
For more information Vibrio and seafood safety information visit:
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