Multi-state outbreaks of acute gastroenteritis traced to fecal-contaminated oysters harvested in Louisiana

Norwalk-like viruses (NLVs), or small round structured viruses, are known t o cause acute gastroenteritis associated with eating contaminated shellfish . Between 1993 and 1996, three oyster-related gastroenteritis outbreaks att ributed to NLV occurred in Louisiana. Intensive trace-back and environmenta l investigations revealed that the overboard disposal of sewage by oyster h arvesters into oyster-bed waters was the most likely source of contaminatio n in at least two of the outbreaks. The small infectious dose of NLV, the l arge quantity of virus particles in stool, and the ability of oysters to co ncentrate virus particles suggest that oster-related outbreaks will continu e unless strong control measures are established. Efforts to halt improper sewage disposal in oyster-harvesting waters, including overboard sewage dis charge, must be undertaken if future outbreaks are to be prevented.