persons in 13 states fell ill after eating raw oysters traced to this location (21). Then, just as these shellfish beds appeared to be safe again, New York authorities forbade the harvest of clams and oysters from beds near Long Island in mid-September, after 10 people became ill from eating raw shellfish collected there. The bacterial pathogen contaminating shellfish in both areas was identified as Vibrio parahaemolyticus. In the summer of 1997, this organism caused another large outbreak in the Pacific Northwest with 209 cases and one death (8). A related species, V. vulnificus, was blamed for two fatalities in Florida in 1998 and for a total of 33 deaths in the U.S. in 1996 (9,20). What kind of bacteria are these vibrios and where do they come from? Vibrios are short, Gram-negative rods, usually found in aquatic environments. Some, such as V. vulnificus and V. parahaemolyticus are halophiles which require a saltwater environment for growth. Both species are normal residents in coastal waters, and their numbers depend on the temperature and salinity of the water (12,15,17). Cell numbers typically increase during the summer as water temperatures rise but they are not positively correlated with indicators of fecal contamination. Therefore, vibrio concentrations are not necessarily higher in shellfish from beds closed to harvesting because of high coliform counts or evidence of sewage contamination. Numerous surveys of raw shellfish from coastal waters of the U.S. have demonstrated a high level of contamination with vibrios. One survey, conducted in the summer, indicated that 100 % of the oysters tested contained detectable V. parahaemolyticus and 67 % containe
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