title: Seroepidemiology of hepatitis B virus infection among children in Mongolia: results of a nationwide survey.
abstract: BACKGROUND
  Because Mongolia is one of the highly endemic countries for hepatitis B virus (HBV) infection in the world, hepatitis B (HB) vaccine was introduced into the National Expanded Program on Immunization in 1991. However, relatively few data are available concerning HBV infection among children born after the start of the program, so far. The aim of the present paper was to describe the seroepidemiology of HBV infection among primary school children using representative national data.
  
  
  METHODS
  In 2004, a nationwide school-based cross-sectional serosurvey was carried out throughout Mongolia, covering both urban and rural areas. Serum samples were tested for hepatitis B surface antigen (HBsAg), antibody to hepatitis B core antigen (anti-HBc) and hepatitis B e antigen (HBeAg) as well as for liver enzymes.
  
  
  RESULTS
  A total of 1145 children aged 7-12 years were studied, which represents nearly 2% of the second grade population of elementary schools in Mongolia. The overall prevalence of HBsAg and anti-HBc was 5.2% (95% confidence interval [CI]: 3.9-6.5%) and 15.6% (95%CI: 13.5-17.7%), respectively. Among HBsAg-positive children 67.8% (95%CI: 55.9-79.7%) were also positive for HBeAg. The prevalence of chronic HBV infection increased by age and was significantly higher among children from rural areas compared to those from urban areas (7.7% vs 3.0%; P < 0.001). In the multivariate logistic regression analysis, rural residence (odds ratio [OR]: 2.57; 95%CI: 1.45-4.58), male sex (OR: 1.9; 95%CI: 1.08-3.26) and age (OR: 1.5; 95%CI: 1.10-2.05) were independent demographic predictors for chronic HBV infection.
  
  
  CONCLUSIONS
  The prevalence of chronic HBV infection has been decreasing in the Mongolian young generation, most likely due to infant HB vaccination. However, significant rural-urban differences in the prevalence of HBV infection were found that demand further investigation to estimate the potential causes.
authors.affiliation: Department of Public Health, Jichi Medical University School of Medicine, Tochigi, Japan. davaamon@jichi.ac.jp
authors.forename: Dambadarjaa
authors.initials: D
authors.lastname: Davaalkham
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Ojima
authors.forename: Pagvajav
authors.initials: P
authors.lastname: Nymadawa
authors.forename: Navaansodov
authors.initials: N
authors.lastname: Tsend
authors.forename: Tserenkhuu
authors.initials: T
authors.lastname: Lkhagvasuren
authors.forename: Steven
authors.initials: S
authors.lastname: Wiersma
authors.forename: Ritei
authors.initials: R
authors.lastname: Uehara
authors.forename: Makoto
authors.initials: M
authors.lastname: Watanabe
authors.forename: Izumi
authors.initials: I
authors.lastname: Oki
authors.forename: Yosikazu
authors.initials: Y
authors.lastname: Nakamura
mesh_terms: D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006509:Hepatitis B / Q000453:epidemiology* / Q000821:virology; D006510:Hepatitis B Antibodies / Q000276:immunology*; D006512:Hepatitis B Core Antigens / Q000276:immunology*; D006514:Hepatitis B Surface Antigens / Q000276:immunology*; D006515:Hepatitis B virus / Q000276:immunology*; D006801:Humans; D007118:Immunoassay; D015994:Incidence; D008297:Male; D008986:Mongolia / Q000453:epidemiology; D015999:Multivariate Analysis; D011159:Population Surveillance / Q000379:methods*; D015995:Prevalence; D011379:Prognosis; D012189:Retrospective Studies; D012424:Rural Population / Q000706:statistics & numerical data; D016036:Seroepidemiologic Studies; D014505:Urban Population / Q000706:statistics & numerical data
chemical_list: D006510:Hepatitis B Antibodies; D006512:Hepatitis B Core Antigens; D006514:Hepatitis B Surface Antigens