The overwhelming majority of human cases of this serious illness occur between spring and fall. The quarantine applies to all species of mussels taken by the public anywhere on the California coast, including all bays and estuaries. No commercially harvested shellfish are included in the annual quarantine. All commercial shellfish harvesters in California must be certified by the state and are subject to stringent testing requirements to ensure that all oysters, clams and mussels entering the marketplace are free of toxins.
Commercial harvesting is stopped immediately if potentially dangerous levels of toxins are found.
In addition, shellfish should be taken for food only from areas free of sewage or chemical contamination. PSP affects the central nervous system, producing a tingling around the mouth and fingertips within a few minutes to a few hours after eating toxic shellfish. This typically is followed by disturbed balance, lack of muscular coordination, slurred speech and difficulty swallowing. In severe poisonings, complete muscular paralysis and death from asphyxiation can occur. It occurs only when populations of a single-celled organism, a dinoflagellate known as Alexandrium catenella , become abundant and concentrated in ocean waters.