Shellfish are filter feeders, and may concentrate microorganisms (bacteria and viruses), as well as natural toxins and chemicals if they are present in the growing waters. The current National Shellfish Sanitation Program (NSSP) dictates uniform requirements that every state must meet, with federal oversight provided by the U.S. Food and Drug Administration (FDA). States are required by the NSSP to maintain minimum sanitation standards addressing issues such as water quality monitoring, harvest area enforcement, training of harvesters and dealers, processing, shipping, and handling.

The U.S. Food and Drug Administration and the Centers for Disease Control and Prevention and state and local partners investigated a multistate outbreak of foodborne illnesses associated with the consumption of raw oysters harvested in Estero El Cardon, Baja California Sur, Mexico between the dates of February 12, 2019 and April 9, 2019.