-- Before cooking, discard any shellfish with open shells.
-- For shellfish in the shell:
Boil until the shells open and continue boiling 5 more minutes or steam until the shells open and continue steaming for 9 more minutes.
Only eat shellfish that open during cooking. Discard shellfish that do not open fully after cooking.
-- For shucked oysters:
Boil for at least 3 minutes, fry in oil for at least 3 minutes at 375 degrees, broil 3 inches from heat for 3 minutes or bake at 450 degrees for 10 minutes.
-- Source: Center for Disease Control