Hepatitis C virus treatment as prevention among injecting drug users: who should we cure first?

Treatment of injecting drug users (IDU) for hepatitis C virus (HCV) infection may prevent onward transmission. Treating individuals who often share injecting equipment is most likely to prevent new infections. However, these high-risk IDU are also more likely to become re-infected than low-risk IDU. We investigated to which group treatment is best targeted.

We modelled the expected benefits per treatment of one chronically HCV-infected IDU in a population of low- and high-risk IDU. The benefits of treating one low- or one high-risk IDU were compared.

Benefits included the probability for the treated IDU to become and remain uninfected, as well as the expected number of prevented infections to others (i.e. we quantified the total expected decrease in chronic infections).

We found a threshold in HCV-RNA prevalence above which treating low-risk IDU, and below which treating high-risk IDU, resulted in the greatest benefits. This threshold was at 50% of exchanged syringes being HCV contaminated. When 42% of IDU engaged in high-risk behaviour (borrowing and lending out syringes 7.3 times more frequently than low-risk IDU), the corresponding threshold of HCV-RNA prevalence among IDU was at 32%. Larger-risk heterogeneity led to a lower corresponding threshold among IDU. A combination of HCV treatment and 50% risk reduction was best directed at high-risk IDU for prevalence among syringes up to 59%. The threshold was marginally sensitive to changes in disease and treatment variables.

When more than half of all exchanged syringes in a population of injecting drug users (IDU) are contaminated by hepatitis C virus, it is most efficient to treat low-risk IDU first. Below this threshold, it is most efficient to treat high-risk IDU first.