title: Epidemiological and genetic analyses of a diffuse outbreak of hepatitis A in Japan, 2010.
abstract: BACKGROUND
  Hepatitis A virus (HAV) is still one of the most common causative agents of acute hepatitis in Japan. Although a relatively small number of annual acute hepatitis A cases (approximately 100-150, 0.78-1.17 per million) were recently reported, a larger number of cases (346, 2.71 per million) were reported in 2010.
  
  
  OBJECTIVE
  To investigate the causes of the 2010 HAV resurgence in Japan by using molecular epidemiological and genetic analyses.
  
  
  METHODS
  HAV specimens were obtained from 61 cases from 22 different prefectures. These viral specimens were genotyped by PCR amplification and sequencing of the VP1/2A region of HAV genome.
  
  
  RESULTS
  Phylogenetic analysis revealed that 61 HAV strains could be divided into three genotypes: IA (44 cases), IB (1 case) and IIIA (16 cases). The IA genotype consisted of two genomic sub-lineages. The sequences of one of the two IA sub-lineages (corresponding to 31 cases) were very similar, 26 of these 31 isolates had 100% identity. The other IA sub-lineage corresponded to strains endemic to Japan. The sequences of Japanese IIIA strains were similar to those of strains that caused a large epidemic in the Republic of Korea from 2007 to 2009.
  
  
  CONCLUSIONS
  The resurgence of HAV in 2010 can be attributed to importation of two newly emerged HAV genotypes.
authors.affiliation: Department of Virology II, National Institute of Infectious Diseases, Japan. kishii@nih.go.jp
authors.forename: Koji
authors.initials: K
authors.lastname: Ishii
authors.forename: Tomoko
authors.initials: T
authors.lastname: Kiyohara
authors.forename: Sayaka
authors.initials: S
authors.lastname: Yoshizaki
authors.forename: Takaji
authors.initials: T
authors.lastname: Wakita
authors.forename: Tomoe
authors.initials: T
authors.lastname: Shimada
authors.forename: Naomi
authors.initials: N
authors.lastname: Nakamura
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Nakashima
authors.forename: Yuki
authors.initials: Y
authors.lastname: Tada
authors.forename: Mamoru
authors.initials: M
authors.lastname: Noda
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D004196:Disease Outbreaks / Q000706:statistics & numerical data*; D005243:Feces / Q000821:virology; D005260:Female; D006506:Hepatitis A / Q000453:epidemiology* / Q000821:virology; D030041:Hepatitis A virus / Q000235:genetics*; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D010802:Phylogeny; D012367:RNA, Viral / Q000032:analysis / Q000097:blood; D012621:Seasons
chemical_list: D012367:RNA, Viral