Emergence of a new Vibrio parahaemolyticus serotype in raw oysters - A prevention quandary

Context In May and June 1998, reported Vibrio parahaemolyticus infections i ncreased sharply in Texas. Objective To determine factors that contributed to the increase in V paraha emolyticus infections. Design, Setting, and Participants Cross-sectional survey of persons reporti ng gas troenteritis after eating seafood in Texas; survey of environmental conditions in Galveston Bay. Main Outcome Measures Traceback of oysters, water quality measures in harve st areas, presence of V parahaemolyticus in stool cultures; comparison of m edian values for environmental conditions before and during the outbreak co mpared with during the previous 5 years. Results Between May 31 and July 10, 1998, 416 persons in 13 states reported having gastroenteritis after eating oysters harvested from Galveston Bay. All 28 available stool specimens from affected persons yielded V parahaemol yticus serotype O3:K6 isolates. Oyster beds met current bacteriologic stand ards during harvest and fecal coliform counts in water samples were within acceptable limits. Median water temperature and salinity during May and Jun e 1998 were 30.0 degrees C and 29.6 parts per thousand (ppt) compared with 28.9 degrees C and 15.6 ppt for the previous 5 years (P<.001). Conclusions This is the first reported outbreak of V parahaemolyticus serot ype O3:K6 infection in the United States. The emergence of a virulent serot ype and elevated seawater temperatures and salinity levels may have contrib uted to this large multistate outbreak of V parahaemolyticus. Bacteriologic monitoring at harvest sites did not prevent this outbreak, suggesting that current policy and regulations regarding the safety of raw oysters require reevaluation. Consumers and physicians should understand that raw or under cooked oysters can cause illness even if harvested from monitored beds. In patients who develop acute gastroenteritis within 4 days of consuming raw o r undercooked oysters, a stool specimen should be tested for Vibrio species using specific media.