Home and Community Care Digest
Methods: Computer simulation was used to estimate the site's impact on the following outcomes: survival; rates of HIV and hepatitis C infection; referral to methadone maintenance treatment; and costs. The simulation used a cohort of people aged 15-64 years in all possible combinations of three health states: HIV status, hepatitis C status, and status of injection drug use (user or not, and a further distinction was made between those who receive methadone treatment and those who do not). A time horizon of 10 years and a discount rate of 5% for costs and life expectancy were used. The primary outcome used to model the effectiveness of the facility was decrease in needle sharing and secondary outcomes were increased use of safer practices when sharing needles, and increased referral to methadone clinics. It was assumed that these behavioural changes would only occur for those who regularly attended the site. The cost-effectiveness analysis (from the perspective of the health system) compared the site's services to interventions for injection drug users provided by other than a supervised drug injection facility.
Findings: The model predicted that the prevalence of HIV and hepatitis C would continue to increase, but at a decreasing rate and that over time, the supervised injection facility would lead to an increase in the size of the injection drug user population due to fewer cases of infection and associated mortality. The most pessimistic scenario would see 1191 cases of HIV and 54 cases of hepatitis C averted over the 10-year horizon. Undiscounted estimates of the cost per case averted over 10 years were $20,100 for HIV and $444,500 for hepatitis C. The net costs of treating hepatitis C and HIV, and methadone maintenance were lower with the facility. In addition, the costs were negative indicating that the facility saves money and improves life expectancy. However, the model was sensitive to three assumptions: 1) facility is not associated with savings if rates of injection drug use were either very low (under 490 injections per year) resulting in low rates of HIV transmission rendering the intervention not worthwhile, or very high (more than 1762 injections per year) increasing the risk of HIV transmission such that the impact of the facility would be minimal, 2) the effectiveness of the facility and other interventions to decrease risks associated with drug injection, and 3) the values used for costs.
Conclusions: An objective simulation of Insite's health outcomes suggests that there are potential cost savings even if a relatively low percentage of users participate. Furthermore, even with conservative assumptions of efficacy to avoid overestimating the benefits, Vancouver's supervised drug injection facility is associated with improved health outcomes and cost savings. Despite the limited generalizability (i.e., data entered into the model are specific for Vancouver), supervised drug injection facilities may be a good harm reduction tool for use across the country.
Bayoumi, A. M., & Zaric, G. S. (2008). The cost-effectiveness of Vancouver's supervised injection facility. CMAJ, 179(11): 1143-1151.
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