Epidemiology and Infection

Special Article

Outbreaks of Norwalk-like virus-associated gastroenteritis traced to shellfish: coexistence of two genotypes in one specimen

M. Sugiedaa1, K. Nakajimaa2 and S. Nakajimaa3 c1

a1 Shizouka Prefectural Institute of Public Health and Environmental Science, 4–27–2, Kitaando, Shizuoka-shi, Shizuoka 420, Japan

a2 Department of Virology, Medical School, Nagoya City University, 1, Kawasumi, Mizuho-chou, Mizuho-ku, Nagoya-shi, Aichi 467, Japan

a3 Department of Microbiology, The Institute of Public Health, 4–6–1, Shirokanedai 4 Chome, Minato-ku, Tokyo 108, Japan


We determined the nucleotide sequences of Norwalk-like viruses in 10 PCR products from stool or oyster specimens obtained from four outbreaks of gastroenteritis in which shellfish was suspected as the cause in Shizuoka prefecture in Japan between 1987–94. The sequences were determined from nucleotide positions 4561–852 (292 bp) in the polymerase region. Two types of sequences were detected. One (genotype 1) had 87% sequence homology with the prototype Norwalk virus, and the other (genotype 2) had 59 % sequence homology. The sequences from isolates belonging to the same genotype were almost the same regardless of the year of isolation. Because sequences of 2 genotypes were detected in 2 of the 4 outbreaks, nested PCR was performed with genotype-specific primers to detect the presence of 2 genotypes in the same specimen. In 5 of 10 specimens, PCR bands were detected with both genotype-specific primers, indicating the coexistence of 2 genotypes in 1 specimen. We also detected two genotypes of Norwalk-like virus in an oyster from a sample implicated in one of the outbreaks which may provide direct evidence of oysters as the cause of the gastroenteritis.

(Accepted December 19 1995)


c1 Author for correspondence.