Background: Prevalence of human immunodeficiency virus (HIV) and hepatitis C virus (HCV) in the injecting drug user (IDU) community can differ considerably. In Australia in 1997, HIV prevalence among attendees at Needle Exchange Programs was 1% while HCV prevalence was 50%. The impact that different needle-sharing behaviour and drug injecting use may have on the future levels of these viruses is uncertain.
Method: We develop a mathematical model of the number of people who inject drugs with each of these infections to determine their changes under different scenarios. The impact of transmission probabilities and needle sharing on the incidence and prevalence of HIV and HCV infections are assessed.
Results: Critical levels of needle sharing, below which total infections would fall to minimal levels, were estimated to be 17 IDU partners per year for HIV compared with 3 IDU partners per year for HCV. Current average levels of needle sharing in Australia are estimated to be six IDU partners per year.
Conclusions: This analysis suggests that under current drug injecting behaviour, HIV prevalence in IDU in Australia should remain below 1% but that HCV prevalence will stay elevated.