Features of neurotoxic shellfish poisoning from recreationally harvested clams in Florida, 2006: Epidemiologic and clinical factors

A series of Neurotoxic Shellfish Poisoning (NSP) cases occurred along the south-west coast of Florida during 2006. NSP is caused by consumption of shellfish contaminated with brevetoxins originating from the marine dinoflagellate, Karenia brevis. K. brevis blooms cause the phenomenon known as red tide, a recurrent environmental hazard in the Gulf of Mexico. Florida state agencies routinely sample coastal waters for K. brevis; testing of regulated shellfish beds has been in place since the 1970's.

Descriptions of NSP cases are rare. In this series, 8 clusters representing 17 individuals were identified. All cases were associated with consumption of recreationally-harvested clams from coastal areas not officially approved or open for harvesting. Most (n=15) cases sought medical attention and treatment at surrounding hospitals. A variety of gastrointestinal and neurological symptoms were reported; neurological symptoms being the predominant clinical presentation. Incubation was from 1-6 hours, symptom duration was a few hours to 2 days, and 7 cases were admitted after emergency room presentation. Available samples of clams from case meals, implicated shellfish beds, and urinalysis from cases were positive for brevetoxins.

Most cases were tourists of Asian ethnicity who were unaware of shellfish bed closures. Increased public health warnings, including public services announcements, radio interviews and door-to-door reverse 911 contacts were initiated; cases abated after July. Despite local knowledge about red tides, routine monitoring of K. brevis cell counts in seawater, successful monitoring of state-regulated shellfish beds and local dissemination of shellfish-risk information; education of transient groups such as tourists remains a challenge.