Recombinant norovirus implicated in gastroenteritis outbreaks in Hiroshima prefecture, Japan

Norovirus (NoV) is a major etiological agent of acute gastroenteritis outbreaks worldwide. A total of 314 fecal specimens collected from patients of 39 NoV gastroenteritis outbreaks in Hiroshima Prefecture, Japan, between December 2001 and April 2006 were tested for the occurrence of recombinant NoVs. Sixteen genotypes (GI/1, GI/2, GI/4, GI/7, GI/8, GI/11, GI/14, GII/2, GII/3, GII/4, G11/5, GII/6, GII/8, GII/12, GII/14, and GII/untypeable) were detected in the 39 outbreaks based on capsid sequences and GII/4 was predominant recently. Twelve strains detected in 11 (28.2%) of the 39 outbreaks were suspected to be recombinants by using Simplot and Recco analyses and five recombinant genotypes, GII/4-GII/12 (five strains), GIIb-GII/3 (four strains), GII/4-GII/ 2 (one strain), GII/4-GII/14 (one strain), and GI/2-GI/8 (one strain), were identified based on RNA-dependent RNA polymerase and capsid sequences. None of the strains genotyped as GII/4 based on the capsid sequence was identified as a recombinant. The putative recombination points in the recombinant strains were placed either upstream or downstream of the open reading frame (ORF) 1 and ORF2 overlap. The present study indicates the following: (a) recombination among ORFs is common in nature, (b) the involvement of recombinant NoVs in gastroenteritis outbreaks is extensive even in a local area such as Hiroshima Prefecture, Japan, and (c) the conserved region (ORF1 and ORF2 overlap) has a meaningful function against the recombination event.