Abstract Body

Background: The incidence of hepatitis C virus (HCV) infections among HIV-infected men who have sex with men (MSM) increased markedly in industrialized countries and is associated with high risk sexual behaviour including traumatic sex. Finding the most effective interventions to control this epidemic is key to reducing liver-related morbidity and mortality in these patients. HCV treatments with direct-acting antivirals (DAAs) achieve high cure rates, but the role of these therapies on reducing HCV transmission remains uncertain.

Methods: Based on behavioural, epidemiological and clinical information collected prospectively in the Swiss HIV Cohort Study (SHCS), we developed a deterministic mathematical model for sexually transmitted HCV infections among HIV-positive MSM in Switzerland. We reproduced the epidemic for the period 2000-2013 and estimated the basic reproductive number R0. We then evaluated the effects of increasing treatment uptake (5-fold increase from the currently observed treatment rate of 0.22/person-year), or of increasing treatment efficacy on reducing the future HCV incidence. Finally, we evaluated the impact of three scenarios of future unsafe sex frequency on HCV incidence.

Results: The best-fit parameter values indicated that the HCV epidemic was mainly driven by the increase in sexual risk behaviour in recent years. The epidemic threshold (R0 = 1) was crossed in 2010. A pessimistic scenario assuming that the frequency of unsafe sex continues to rise predicts a steep increase in HCV incidence, with little differences between treatment strategies (Figure). A scenario where the frequency of unsafe sex remains stable results in declining HCV incidence with or without DAA therapy, provided that treatment rate increases considerably. The optimistic assumption that the frequency of unsafe sex reduces considerably leads to an immediate and steep decrease in the future HCV incidence, even in the absence of improvements in treatment rate and/or efficacy (Figure).

Conclusions: Treatment interventions are only effective in reducing HCV transmission among HIV-infected MSM if the frequency of high risk sexual behaviour does not increase as in recent years. However, if unsafe sex behaviour stabilizes, increased treatment uptake and efficacy are predicted to curb the epidemic within 10 years.

Figure. Projected HCV incidence in HIV-infected MSM assuming different treatment and behavioural scenarios.