title: Characterization of Occult Hepatitis B Infection Among Injecting Drug Users in Tehran, Iran.
abstract: BACKGROUND
  Hepatitis B virus (HBV) infection is a major health problem worldwide.
  
  
  OBJECTIVE
  The aim of this study was to investigate the frequency of occult hepatitis B infection (OBI) and its associated risk factors, together with the molecular characterization of the virus in injecting drug users of Tehran.
  
  
  METHODS
  The study consisted of 229 injecting drug users. Serum samples were collected and tested for the presence of hepatitis B core antibody (HBcAb) and hepatitis B surface antigen (HBsAg) by an enzyme-linked immunosorbent assay (ELISA). HBV B virus DNA was extracted from the serum samples, and a fragment of the S gene was amplified using the nested polymerase chain reaction. The genotype, subgenotypes, subtype, and S gene mutation of HBV were determined by direct sequencing. A phylogenetic tree was constructed using the neighbor-joining method.
  
  
  RESULTS
  Sixty-four (28%) participants were HBcAb positive, 59 cases were HBcAb positive and HBsAg negative, and 5 cases were HBsAg positive. Hepatitis B DNA was found in three HBsAg-positive cases. Thirteen of 59 (22%) individuals were hepatitis B DNA positive. The phylogenetic tree of hepatitis B DNA showed the existence of genotype D. The only significant correlation was between sharing a syringe and OBI.
  
  
  CONCLUSIONS
  In comparison with the rate of HBcAb positivity reported in other Iranian studies, the rate was higher in the present study. There were a few variations, genotypes, and subtypes among the infected injecting drug users. Further investigations are needed to unravel the molecular characterization of OBI.
authors.affiliation: Infectious Diseases and Tropical Medicine Research Center, Shahid Beheshti University of Medical Sciences, Tehran, IR Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Asli
authors.affiliation: Department of Microbiology, Faculty of Biological Sciences, Shahid Beheshti University, Tehran, IR Iran.
authors.forename: Tahmineh
authors.initials: T
authors.lastname: Kandelouei
authors.affiliation: Department of Microbiology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, IR Iran.
authors.forename: Koroush
authors.initials: K
authors.lastname: Rahimyan
authors.affiliation: Department of Immunology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, IR Iran.
authors.forename: Foad
authors.initials: F
authors.lastname: Davoodbeglou
authors.affiliation: Department of Microbiology, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, IR Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Vaezjalali
keywords: Genotype; Hepatitis B; Hepatitis B Surface Antigen; Injecting Drug User