Modelling the spread of hepatitis C virus infection among injecting drug users in Glasgow: implications for prevention

Stochastic simulation was used to model quantitatively the transmission of HCV through the sharing of used needles/syringes among IDUs in Glasgow. This combined information on (a) the incidence and cessation of injecting drug use, (b) the frequencies with which IDUs injected and shared needles/syringes, and (c) the susceptibility, transmissibility and carriage of HCV infection. The model that considered higher infectivity following infection produced seroprevalences (median: 62–72%) and incidences (18–30 per 100 susceptible injector-years) consistent with observed data during the 1990s. The annual number of new HCV infections among Glasgow IDUs was estimated to be low during 1960–1976 (median: 10–60), rise steeply during the early 1980s to peak in 1985 (1120), stabilise during 1991–1997 (510–610) and rise again during 1998–2000 (710–780). Scenario analyses indicated that 4500 HCV infections (10th–90th percentiles: 2400–7700) had potentially been prevented in Glasgow during 1988–2000 as a result of harm-reduction measures. Also, HCV incidence can be successfully reduced if IDUs who, unavoidably, share needles/syringes confine their borrowing to one person; with this strategy alone, an estimated 5300 HCV infections (10th–90th percentiles: 4100–6700) could have been averted in Glasgow during 1988–2000. Such insights will inform those responsible for developing new ways to prevent HCV transmission among IDU populations.