Serious illness which is a consequence of consumption of bivalve shellfish (mollusks) such as mussels, oysters and clams that have ingested, by filter feeding, large quantities of micro-algae containing a group of high molecular weight polyethers such as okadaic acid, dinophysis toxins, pectenotoxins, and yessotoxin; gastroenteritis develops shortly after ingestion and generally lasts 1-2 days.