Unexpectedly high proportion of drug users and men having sex with men who develop chronic hepatitis B infection.

Background & Aims: In low endemic countries, most hepatitis B virus (HBV) infections are found in adult behavioural risk groups, such as drug users (DU) and men having sex with men (MSM). These risk groups are frequently exposed to HBV, which might induce a different rate of viral clearance compared with the general adult population, in whom the chronicity rate is estimated to be 5-10%. Our aim was to obtain insights into the proportion of MSM and DU developing chronic infection after a primary HBV infection, and the underlying risk factors.

Methods: From 1984 to 2002, sera of 1862 MSM and 1268 DU of the Amsterdam Cohort Studies were retrospectively tested for anti-HBc, HBsAg, and HBV DNA. As of 2003, all of the cohort participants were vaccinated, making further testing redundant.

Results: Hundred and forty seven participants seroconverted for anti-HBc during follow-up. The median age at the moment of the acute infection was 31 years. The proportion of those becoming chronically infected was 23% and 28% for MSM and DU, respectively. In both cohorts, being younger was a risk factor for developing chronic infection (OR: 0.9; 95% CI: 0.82-0.99). HIV/HCV co-infection was associated with developing chronic HBV infection in the DU cohort (OR: 32.1, 95% CI: 3.1-334.5).

Conclusions: Compared with the general population, MSM and DU had an unanticipated high rate of developing chronic HBV infections. HIV/HCV co-infection proved to be an important risk factor for developing chronic HBV infections in DU. The reason for the high rate of MSM becoming chronically infected remains unclear.