Evaluating Vancouver's supervised injection facility: data and dollars, symbols and ethics

Drs. Des Jarlais, Arasteh, and Hagan provide a thoughtful commentary on our article. Although we calibrated our model to epidemiological data for Vancouver, yielding an incidence rate among injection drug users of about 5 to 6 cases per 100 person-years, we recognize that these estimates are uncertain. However, an incidence rate of 1 case per 100 person-years, as suggested by Des Jarlais and Arasteh, is almost certainly too low for Vancouver. Caution should be exercised when extrapolating from recent VIDUS data since the low reported incidence rates are likely biased due to exhaustion of a fixed cohort.¹ Recent estimates from Vancouver and Montreal suggest a persistently high incidence rate.^2,3

Nevertheless, the most salient question is not which incidence estimate is correct but rather whether the findings of our analysis would change with different assumptions. This is the reason that simulation models, including ours, are subjected to extensive sensitivity analysis. The commentary authors hypothesize a rate of 4 to 5 per 100 person-years for Vancouver if no supervised injection facility were in place. If we adjust our risk of transmitting HIV per needle-sharing event downward (to incorporate effects such as partner restriction and informed altruism) to yield an incidence rate of 4 cases per 100 person-years, our model still predicts that the supervised injection facility, under the most conservative assumptions about efficacy, would be cost-saving; at 3 cases per 100 person-years, the cost-effectiveness ratio would be $19,400 per life year gained. This latter estimate is approximately equal to the incremental cost-effectiveness of methadone maintenance therapy, a widely accepted treatment for injection drug users, and is within the range that would normally be considered cost effective.

1. Boileau C, Bruneau J, Al-Nachawati H, Lamothe F, Vincelette J. A Prognostic Model for HIV Seroconversion Among Injection Drug Users as a Tool for Stratification in Clinical Trials. JAIDS J Acquired Immune Defic Syndromes. 2005;39:489-95.
2. Remis RS. HIV incidence among injection drug users in Vancouver. CMAJ. 2002;166:908-9.
3. Wood E, Lloyd-Smith E, Li K, Strathdee SA, Small W, Tyndall MW, et al. Frequent Needle Exchange Use and HIV Incidence in Vancouver, Canada. Am J Med. 2007;120:172-9.

Ahmed M. Bayoumi, Centre for Research on Inner City Health, St. Michael's Hospital, Toronto ON

Gregory M. Zaric, Richard Ivey School of Business, University of Western Ontario, London ON

Conflict of Interest:

None declared