How does the consumer know that shellfish are safe to eat?

Clams and oysters in the shell should be alive and the shells should be closed tightly or should close when the mollusks are tapped. The U.S. Public Health Service, in cooperation with the States, has a sanitation control program that covers the labeling and shipment of clams, mussels, and oysters. These shellfish may be harvested only from non-polluted waters and processed for shipment in sanitary plants inspected by State shellfish inspectors. Authorities periodically test water for sewage pollution and ban catches from polluted areas.