[A food poisoning outbreak caused by purple Washington clam contaminated with norovirus (Norwalk-like virus) and hepatitis A virus].

A party of 57 people dined together in a restaurant in Hamamatsu City on December 11, 2001. The next day, 22 of them developed symptoms of acute gastroenteritis, such as diarrhea, vomiting, and fever. Examination of 4 fecal specimens from these patients by ELISA for Norovirus (Norwalk-like virus, NV) detected both genogroup I (GI) and genogroup II (GII) NV in all the 4 specimens. In addition, RT-PCR and real-time PCR methods for NV detected the NV gene. Approximately one month after the outbreak of the food poisoning (acute gastroenteritis) by NV, 4 individuals in the same party developed type A hepatitis. Both RT-PCR and real-time PCR methods for hepatitis A virus (HAV) detected the HAV gene in their fecal specimens. The party of these patients ate purple Washington clam (Saxidomus purpuratus, imported from China) steamed with red pepper. Since this food appeared to have caused the viral infections, the one with the same lot number was subjected to viral examinations, which successfully detected the NV GI, NV GII, and HAV genes. These results led to the conclusion that the clam contaminated with NV and HAV had caused the food poisoning. The DNA sequences of the NV detected in the patients and the clam had 74 to 99% homology, indicating strains of various genotypes. All the strains of HAV that were derived from the patients and the clam were genotype 1A, and these sequences had over 95% homology, but were not completely identical. This outbreak led to the demonstration of imported fishery products as a cause of type A hepatitis, and indicated the need for guiding and enlightening people on the importance of adequate cooking of bivalves.