Background Human immunodeficiency virus (HIV) outbreaks occur among injecting drug users (IDUs), but where HIV is low insight is required into the future risk of increased transmission. The relationship between hepatitis C virus (HCV) and HIV prevalence among IDUs is explored to determine whether HCV prevalence could indicate HIV risk.
Methods Systematic review of IDU HIV/HCV prevalence data and regression analysis using weighted prevalence estimates and time–series data.
Results HIV/HCV prevalence estimates were obtained for 343 regions. In regions other than South America/sub-Saharan Africa (SAm/SSA), mean IDU HIV prevalence is likely to be negligible if HCV prevalence is <30% (95% confidence interval 22–38%) but increases progressively with HCV prevalence thereafter [linearly (β = 0.39 and R2 = 0.67) or in proportion to cubed HCV prevalence (β = 0.40 and R2 = 0.67)]. In SAm/SSA, limited data suggest that mean HIV prevalence is proportional to HCV prevalence (β = 0.84, R2 = 0.99), but will be much greater than in non-SAm/SSA settings with no threshold HCV prevalence that corresponds to low HIV risk. At low HCV prevalences (<50%), time–series data suggest that any change in HIV prevalence over time is likely to be much smaller (<25%) than the change in HCV prevalence over the same time-period, but that this difference diminishes at higher HCV prevalences.
Conclusions HCV prevalence could be an indicator of HIV risk among IDUs. In most settings, reducing HCV prevalence below a threshold (30%) would reduce substantially any HIV risk, and could provide a target for HIV prevention.