Analytical approach:
This economic evaluation was based on a dynamic state-transition model intended to simulate the natural history of the population of injection drug users, non-users, and those with HIV or HCV infection, as well as combinations of these states, in Vancouver, British Columbia. The time horizon of the analysis was 10 years. The authors stated that the perspective of the health care system was adopted.
Effectiveness data:
The bulk of clinical evidence was Vancouver-specific including both published and unpublished data from cohorts in the Vancouver Injection Drug Users Study and the Scientific Evaluation of Supervised Injecting (SEOSI) study. These data were supplemented with estimates from the literature and authors’ opinions. Some information on the published sources was provided in a technical appendix, in which the authors justified the selection of their estimates. In general, the data from North American studies were selected. Three measures of the efficacy of the intervention were considered: decreased needle sharing; decreased needle sharing and increased use of safer practices when sharing injections; and decreased needle sharing, increased use of safer practices, and increased referral for methadone treatment.
Monetary benefit and utility valuations:
Not relevant.
Measure of benefit:
Life-years (LYs) were used as the primary benefit measure. A 5% annual discount rate was applied. Cases of HIV or HCV infections averted were also considered.
Cost data:
The costs included those of treatment for HIV infection and HCV infection, health services for injection drug users (with or without methadone therapy), methadone maintenance treatment, operating costs of the supervised facility, and usual care for the general population (non-users without HIV or HCV infections). The costs were reported as macro-categories and the unit costs and resource quantities were not presented separately. The sources used were described in the technical appendix. In general, Canadian studies were used. The cost of the supervised facility was derived from the SEOSI study. The price year was 2008 and all costs were in Canadian dollars (CAD).
Analysis of uncertainty:
A deterministic sensitivity analysis was undertaken in order to consider the impact on the cost-effectiveness ratios of variations in the model inputs. The ranges of values were based on confidence intervals derived from the literature or based on authors’ opinions. Wider ranges were also considered when the authors were concerned about biased estimates.