title: Detection and genetic characterization of norovirus infections in children with acute gastroenteritis in Japan, 2007-2009.
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 Chiba 407 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.
authors.affiliation: Department of Developmental Medical Sciences, School of International Health, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
authors.forename: Wisoot
authors.initials: W
authors.lastname: Chan-It
authors.forename: Aksara
authors.initials: A
authors.lastname: Thongprachum
authors.forename: Shoko
authors.initials: S
authors.lastname: Okitsu
authors.forename: Shuichi
authors.initials: S
authors.lastname: Nishimura
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kikuta
authors.forename: Tsuneyoshi
authors.initials: T
authors.lastname: Baba
authors.forename: Atsuko
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Kumiko
authors.initials: K
authors.lastname: Sugita
authors.forename: Shintaro
authors.initials: S
authors.lastname: Hashira
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tajima
authors.forename: Masashi
authors.initials: M
authors.lastname: Mizuguchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ushijima
mesh_terms: D000293:Adolescent; D017250:Caliciviridae Infections / Q000150:complications* / Q000175:diagnosis / Q000453:epidemiology / Q000821:virology*; D002648:Child; D002675:Child, Preschool; D005243:Feces / Q000821:virology; D005260:Female; D005759:Gastroenteritis / Q000453:epidemiology / Q000209:etiology* / Q000821:virology*; D014644:Genetic Variation; D006801:Humans; D007223:Infant; D007564:Japan / Q000453:epidemiology; D008297:Male; D017720:Molecular Epidemiology; D029322:Norovirus / Q000235:genetics / Q000502:physiology*; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction