Be wary of raw or undercooked oysters, especially those harvested in the Gulf Coast and Chesapeake Bay during warmer months. They are particularly vulnerable to Vibrio vulnificus, a bacterium that occurs naturally in marine waters but multiplies rapidly in warm weather.
Contaminated oysters can cause mild illness in healthy people, but severe illness in those with health problems.
Some retailers and restaurants sell oysters specially treated to kill Vibrio. However, these processes may not destroy all bacteria or other pathogens, including Norovirus, which oysters can carry any time of year due to contaminated waters.
People with compromised immunity or other chronic medical conditions (such as liver disease), pregnant women, young children, the elderly and anyone in frail health should avoid raw or undercooked oysters.