We evaluated the cost-effectiveness of Vancouver's supervised injection facility and estimated the number of cases of HIV and hepatitis C virus infections that could be averted owing to decreased needle sharing, safer injecting practices and increased referral to methadone maintenance treatment. Our estimate for the base assumption — that decreased needle sharing would be the only effect of the facility — was conservative. On the basis of that assumption, we calculated that the use of the facility would be associated with improved survival and fewer net costs. When we incorporated the other 2 treatment effects, the facility was even more economically attractive. We found that there would be potential cost savings even if a relatively low percentage of injection drug users were to use the facility. Our estimate compares favourably with those associated with other health care interventions.51,52
For context, estimates of the cost-effectiveness of methadone maintenance treatment range from about $5000 to $20 000 per life-year gained.18,53
The prime determinant of cost-effectiveness in our model was the number of HIV infections averted through decreased needle sharing. When the average number of injections was low or high, the facility was less economically attractive. If the number was low, too few transmissions would occur to make the intervention worthwhile. If the number was high, the risk of transmission would be so high that the facility's impact would be minimal. Sexual transmission of HIV and transmission of hepatitis C virus made relatively minor contributions. One limitation of our model is that we did not include an extended time frame beyond 10 years. Thus, we did not fully account for future costs, which may be particularly important when considering HIV-related therapy. Our finding of a cost of $20 100 per case of HIV infection averted may be instructive in this regard, since the lifetime costs of direct HIV-related care exceeds this estimate, by a factor of about 10.54
Supervised injection facilities exist in over 2 dozen cities in Europe and Australia.55–57
An economic evaluation of the safe injection facility in Sydney, Australia, used a cost–benefit approach and estimated that the ratio of benefits to costs may not be favourable at start-up but would probably become so in the future.58
A previous analysis of Vancouver's facility indicated a favourable cost–benefit ratio and a cost of $52 000–$155 000 per case of HIV infection averted, which is considerably higher than our estimate.6
However, that analysis used a simpler model than ours, it focused solely on cases of HIV infection averted, and it did not account for dynamic transmissions in an epidemic model.
In our base analysis, the prevalence of HIV infection among injection drug users continued to increase over time. This reflected how the incidence of new cases of HIV infection in this population exceeded mortality with combination antiretroviral therapy. The prevalence of HIV infection also increased, although at a reduced rate, when the introduction of the supervised injection facility was considered in the model. The same was true for the prevalence of hepatitis C virus infection. In reality, however, the difference in rates with and without the facility will not be observed, because the “no facility” scenario does not exist in Vancouver. Thus, expecting the prevalence of HIV or hepatitis C virus infection to fall relative to historical controls is too stringent a criterion for evaluating effectiveness. More generally, our observations indicate the challenge of evaluating an intervention without a contemporary control group and underscore the importance of considering intermediate outcomes, such as temporal trends in injecting practices, alongside epidemiologic data.
Our model has several limitations. First, we modelled the efficacy of the facility by focusing on the injecting behaviours of regular users of the facility. We may have overestimated efficacy if injection practices of users injecting outside the facility did not change; however, available analyses to date suggest a general change in injecting practices.3
We may also have underestimated efficacy by ignoring the decreased risk associated with injections within the facility by casual users.
Second, we excluded from our analysis potentially important health benefits such as decreased overdose, reduced transmission of hepatitis B, and reduced incidence of soft-tissue infections, endocarditis and other harms associated with unhygienic injection. We also did not account for benefits such as increased access to, and delivery of, other health services, social services and crisis management as well as societal benefits such as decreased cost of crime and improved social order, which may be particularly important in economic terms.59
Third, we considered methadone maintenance treatment as the only form of drug addiction treatment and not more expensive treatments such as residential care.
Finally, we did not consider quality of life or a full probabilistic analysis.
Our estimates are specific to the characteristics of the Vancouver supervised injection facility and may not be generalizable to other settings, since the size and geographic location of the population of injection drug users and the baseline prevalence of HIV and hepatitis C virus infections will differ across cities.
Our analysis indicates that the supervised injection facility in Vancouver is associated with improved health outcomes. These health benefits and cost savings are due in large part to averted cases of HIV infection, even with conservative estimates of efficacy.
@@ See related commentary by Des Jarlais and colleagues, page 1105