Woman eating a delicacy oyster, close-up at a restaurant

Beware: Severe Illnesses are Linked to the Consumption of Raw Oysters

June 2019

by R. Sivaprasad, M.D., Chief of Infectious Diseases (Ret.), Monmouth Medical Center, RWJBarnabas Health 


Eating raw oysters and certain undercooked shellfish such as clams and mussels can put individuals at risk for infections. Oysters eat by constantly drawing in water and the materials in the water, including harmful bacteria and viruses. These bacteria and viruses can become concentrated in an oyster’s body and infect people who eat raw or undercooked oysters. One of the infections from eating raw oysters is caused by Vibrio, a genus of bacteria, several species of which can cause foodborne infection called vibriosis. Vibrio occurs naturally in coastal waters where oysters grow.   

Every year in the United States, about 80,000 people get vibriosis and 100 people die from it.  Most of these illnesses happen from May through October, when water temperatures are warm.  However, people can get sick from eating raw or undercooked oysters during any month of the year. Oysters that contain harmful bacteria don’t look, smell or taste different from other oysters.  The only way to kill harmful bacteria in oysters is to cook them properly.

Most Vibrio infections usually result in diarrhea and vomiting. Some people can get very sick because the infection can result in bloodstream infections. When the emergency room or the physician is contacted, one should report if raw shellfish was eaten or there was contact with brackish or saltwater (brackish water is a mixture of fresh and sea water).

Anyone can get sick from vibriosis, but certain individuals are more susceptible to infections and complications if they have the following problems: liver disease, alcoholism, cancer, diabetes, HIV; or, are taking immunosuppressive therapy for cancers or drugs to lower stomach acid levels.

The following tips are useful to avoid contracting infections from oysters or other shellfish:  

  • Only order fully cooked oysters at restaurants. 
  • Wash hands with soap and water after handling raw seafood.
  • Do not eat raw or undercooked oysters or other shellfish.
  • Before cooking, discard any shellfish with open shells. 
  • Fully cook oysters at home before eating. Hot sauce or lemon juice alone does not kill Vibrio.  
  • For oysters in the shell, boil until the shells open and continue boiling three to five minutes; or, steam until the shells open and continue steaming for four to nine more minutes.

Even experienced oyster lovers are unable to distinguish a good oyster from an infected one.


R. Sivaprasad, M.D., Emeritus Attending, Dept. of Medicine; Chief of Infectious Diseases (Ret.); Past President, Medical Staff, Monmouth Medical Center RWJBarnabas Health.

Editor’s Note: Oysters should be purchased fresh in the shell, when possible, and only from a trusted purveyor. Select oysters with tightly closed shells and discard those with cracked shells or shells trapped with slime and mud. They should be stored in the refrigerator, flat (not stacked), round side down, and over ice.  They can be safely stored for several days. Do not freeze them.





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