Abstract

Background: Noroviruses are a major cause of epidemic gastroenteritis in children and adults. The aim of the present study was to investigate the molecular epidemiology of norovirus gastroenteritis in Japan.
Methods: A total of 954 fecal specimens collected from infants and children with acute gastroenteritis from five different regions (Tokyo, Sapporo, Saga, Osaka, and Maizuru) of Japan during 2007-2009 were identified by multiple RT-PCR and semi-nested PCR.
Results: Norovirus was detected in a relatively high detection rate (26.6 %; 254 of 954). Of the identified NoV, 9.5 % (91 of 954) were positive by semi-nested PCR. Norovirus GII (97.3 %) was more prevalent than GI (2.7 %). Norovirus infections were very common in the patients aged 12-23 months (44.5 %; 113 of 254). Winter month seasonality supported norovirus infection in Japan. All 7 GI sequences (100 %) detected only in 2007-2008 clustered with Chiba407 known as GI.4 genotype. Most of the norovirus GII sequences in 2007-2008 belonged to GII.4 (77.9 %), followed by GII.14 (11.9 %), and GII.3 and GII.6 (5.1 % each). In 2008-2009, norovirus sequences were classified into eight distinct genotypes (GII.1, GII.2, GII.3, GII.4, GII.6, GII.7, GII12, and GII.14). GII.4/2006b variant was responsible for 100 % among the detected GII.4 strains in both seasons. Interestingly, GII.6/GII.14 recombinant strains emerged, for the first time in Japanese children, as the second prevalent genotype (11.9 %) in 2007-2008 and then dropped rapidly to 2.3 % in a year after. In addition, GII.b/GII.3 and GII.4/GII.3 recombinant strains that had been described previously were also found in this study.
Conclusions: This is the first report to demonstrate the co-circulation of the predominant GII.4/2006b variant and the emerging GII.6/GII.14 recombinant strains and supports the importance of norovirus as a causative agent of diarrhea in Japanese children with acute gastroenteritis.

DOI: Clin. Lab. 2011;57:213-220