Benefits of hepatitis C virus treatment: a balance of preventing onward transmission and re-infection

By treating HCV-infected injecting drug users (IDUs), we may prevent infections to other IDUs. Curing preferentially individuals who most often share injecting equipment has the advantage of preventing more infections. However, such high risk behavior IDUs are also more likely to become re-infected. We have created a model that can inform us about most efficient HCV treatment policy; the expected benefits per treatment of one HCV-infected IDU are calculated, defined as a decrease in the number of chronic HCV infections. This includes the probability that the cured IDU remains uninfected, and the number of new infections prevented both directly and indirectly in further infection generations. We explore analytically how these benefits depend on the syringe sharing frequency of the cured IDU. We find that whom to best cure is determined by the prevalence of HCV contamination among exchanged syringes within the IDU population. Treating lowest risk IDUs is most beneficial above a certain prevalence of contamination, since the term for re-infection dominates the equation in this domain. At lower prevalence treating highest risk IDUs is most beneficial, since here the term for prevention dominates. In a much simplified model the threshold between domains is found at exactly 50% HCV prevalence. The threshold value is lowered when taking HCV induced mortality or increased infectiousness during an acute stage of infection into account. It is increased when taking into account treatment duration, or when HCV-treatment is combined with intervention that reduces the syringe sharing rate of the cured IDU.