December 16, 2017

Why Undercooked Oysters Can Make You Sick

Public Health-King County is telling consumers why raw oysters can make you sick. Jenny Lloyd, one of the epidemiologists who has been investigating foodborne illness outbreaks linked to oysters in that state, answered some questions.

Oysters on Plate

The current outbreaks in Seattle have been caused by Vibrio bacteria. That bacteria lives in marine waters. Their numbers increase during the warm summer months, which explains the current crop of outbreaks. Since oysters are filter feeders, the bacteria concentrate in their flesh. Eating raw or undercooked shellfish, especially oysters, is the main risk for contracting this illness.

Most seafood should be cooked to an internal temperature of 145°F. Fish should be opaque and separate easily when tested with a fork. Clams, mussels, and oysters should open completely during cooking. Throw out ones that don’t open. Scallops should be cooked until the flesh is opaque and firm, and shrimp and lobster cooked until the flesh becomes pearly and opaque. Other food safety instructions go further. Safe Oysters at University of Georgia says that shellfish should be boiled for 3 to 5 minutes after the shells open, or steamed for 4 to 9 minutes.

To prevent these illnesses, it’s important to keep raw shellfish cold and cook them thoroughly. Anyone with a chronic illness or compromised immune systems, or anyone who routinely takes antacids is more likely to get very sick with this infection.

The symptoms of a Vibrio infection are watery diarrhea, abdominal cramps, nausea, vomiting, fever, and chills. People usually get sick within 24 hours of exposure to the pathogenic bacteria, but can become ill within four hours. Most people are sick for about three to five days.

Commercial harvesters guard against this type of contamination because they have to follow strict refrigeration and handling requirements. The shellfish growing areas off the coast are monitored for all kinds of pathogens, including Vibrio. If you choose to harvest shellfish yourself, you can protect yourself. Check the biotoxin status of the beach you plan to visit. Harvest as soon as possible after the tide goes out. Do not harvest oysters exposed to direct sunlight, and refrigerate or ice oysters immediately after they are harvested.



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