Six studies (2,986 participants) were included in the review. There were 919 individuals who were hepatitis C virus antibody-negative and had complete case data, of which 40 became hepatitis C virus positive.
At baseline, 57% of injecting drug users reported exposure to opiate substitution therapy, and 67% were classified as high needle and syringe programme coverage.
New hepatitis C virus infection
Based on the augmented data, opiate substitution therapy significantly reduced the incidence of hepatitis C virus transmission among injecting drug users (OR 0.45, 95% CI 0.25 to 0.82). However, there was evidence of some heterogeneity (Ι²=47.7%). High needle and syringe programme coverage did not significantly reduce the incidence of hepatitis C virus transmission among injecting drug users (OR 0.58, 95% CI 0.30 to 1.15); there was no evidence of heterogeneity for this result (Ι²=0.0%).
Based on the analysis with the augmented data points removed, opiate substitution therapy significantly reduced the incidence of hepatitis C virus transmission among injecting drug users (OR 0.36, 95% CI 0.19 to 0.70). High needle and syringe programme coverage also significantly reduced the incidence of hepatitis C transmission among drug users (OR 0.52, 95% CI 0.28 to 0.99).
Self-reported injecting risk behaviour
Participants who were on full harm reduction (that were receiving opiate substitution therapy and reported high needle and syringe programme coverage) were at a significantly lower risk of new hepatitis C virus infection (OR 0.19, 95% CI 0.08 to 0.47) compared with those at minimal harm reduction. There was no statistically significant difference in the risk of new hepatitis C virus infection for those on partial harm reduction compared to minimal harm reduction.
The results for the adjusted analysis (adjusted for gender, injecting duration, injecting crack and homelessness) were similar to the main results. Female gender, homelessness and injecting crack cocaine were associated with a higher risk of new hepatitis C virus infection.
Results were also presented for the effects of opiate substitution therapy and needle and syringe programmes on injecting risk behaviours.