By Liz Highleyman

Due to overlapping routes of transmission -- including sharing of equipment used to inject drugs -- many individuals are coinfected with both hepatitis B virus (HBV) and hepatitis C virus (HCV). Much remains to be learned about how these viruses interact in the body, but studies suggest that they may inhibit each other.

As reported in the September 2008 Journal of Viral Hepatitis, F.C. Tseng of the National Cancer Institute and colleagues examined relationships between HBV infection, HCV infection, and other factors among injection drug users (IDUs) with detectable antibodies against both viruses.

Participants enrolled in a cross-sectional study during 1998-2000 were considered to have been infected with HBV if they had hepatitis B core antibodies, and chronically infected if they had hepatitis B surface antigen (HBsAg). They were considered to have been infected with HCV if they had anti-HCV antibodies, and chronically infected if they had detectable HCV RNA.

Results

• Among 1694 individuals with antibodies to both viruses, HBsAg prevalence decreased with increasing age among those who had detectable HCV RNA (from 4.55% in those aged 18-29 to 1.03% in those > 50 years; P = 0.02).

• HBsAg prevalence did not decrease with age, however, among participants who were HCV RNA negative.

• Chronic HBV infection was less common overall among individuals with chronic HCV infection (odds ratio [OR] 0.25; P < 0.0001).

• This inverse relationship was much stronger in the oldest (> 50 years) age group (OR = 0.15) than in the youngest (18-29 years) group (OR = 0.81) (P = 0.03).

• Similar results were obtained when duration of injection drug use was substituted for age (P = 0.05).

"Among IDUs who have acquired both HBV and HCV, chronic HBV infection is much less common among those with chronic HCV infection, but this inverse relationship increases markedly with increasing years of age and injection drug use," the study authors concluded. "Coinfection with HCV may enhance the resolution of HBsAg during the chronic phases of these infections."

One implication of this finding is that treatment that suppresses or eradicates HCV might allow a resurgence of HBV replication, as suggested by another recent study.

10/17/08

Reference
FC Tseng, BR Edlin, M Zhang, A Kral, and others. The inverse relationship between chronic HBV and HCV infections among injection drug users is associated with decades of age and drug use. Journal of Viral Hepatitis 15(9): 690-698. September 2008. (Abstract).