Relative effects of antiretroviral therapy and harm reduction initiatives on HIV incidence in British Columbia, Canada, 1996-2013: a modelling study

Abstract

Background: Antiretroviral therapy (ART) and harm reduction services have been cited as key contributors to control of HIV epidemics; however, the specific contribution of ART has been questioned due to uncertainty of its true efficacy on HIV transmission through needle sharing. We aimed to isolate the independent effects of harm reduction services (opioid agonist treatment uptake and needle distribution volumes) and ART on HIV transmission via needle sharing in British Columbia, Canada, from 1996 to 2013.

Methods: We used comprehensive linked individual health administrative and registry data for the population of diagnosed people living with HIV in British Columbia to populate a dynamic, compartmental transmission model to simulate the HIV/AIDS epidemic in British Columbia from 1996 to 2013. We estimated HIV incidence, mortality, and quality-adjusted life-years (QALYs). We also estimated scenarios designed to isolate the independent effects of harm reduction services and ART, assuming 50% (10-90%) efficacy, in reducing HIV incidence through needle sharing, and we investigated structural and parameter uncertainty.

Findings: We estimate that 3204 (upper bound-lower bound 2402-4589) incident HIV cases were averted between 1996 and 2013 as a result of the combined effect of the expansion of harm reduction services and ART coverage on HIV transmission via needle sharing. In a hypothetical scenario assuming ART had zero effect on transmission through needle sharing, we estimated harm reduction services alone would have accounted for 77% (upper bound-lower bound 62-95%) of averted HIV incidence. In a separate hypothetical scenario where harm reduction services remained at 1996 levels, we estimated ART alone would have accounted for 44% (10-67%) of averted HIV incidence. As a result of high distribution volumes, needle distribution predominantly accounted for incidence reductions attributable to harm reduction but opioid agonist treatment provided substantially greater QALY gains.

Interpretation: If the true efficacy of ART in preventing HIV transmission through needle sharing is closer to its efficacy in sexual transmission, ART's effect on incident cases averted could be greater than that of harm reduction. Nonetheless, harm reduction services had a vital role in reducing HIV incidence in British Columbia, and should be viewed as essential and cost-effective tools in combination implementation strategies to reduce the public health and economic burden of HIV/AIDS.

Funding: BC Ministry of Health; National Institutes of Health (R01DA041747); Genome Canada (142HIV).

Figure 1. Flow chart of the model

ART=antiretroviral treatment; The model shows movement for individuals in each of the risk behaviour strata (MSM, PWID, MSM/PWID, Heterosexual). Individuals can transition to mortality from any of the model states (transitions not shown). A more comprehensive description of the model, with specific references to parameters used for each transition, is provided in the appendix.

Figure 2. Percentage of incident HIV infections averted attributable to harm reduction services and the preventive benefits of ART via needle sharing

Panel A: Estimated independent effects of harm reduction services and ART on HIV incidence among PLHIV Panel B: Estimated independent effects of needle distribution and OAT on HIV incidence among PLHIV Grey-shaded area represents the combined effect of harm reduction (including NDP and OAT) and ART (Scenario S1) * indicates baseline ART efficacy assumption in reducing HIV transmission via needle sharing.

Figure 2. Percentage of incident HIV infections averted attributable to harm reduction services and the preventive benefits of ART via needle sharing

Panel A: Estimated independent effects of harm reduction services and ART on HIV incidence among PLHIV Panel B: Estimated independent effects of needle distribution and OAT on HIV incidence among PLHIV Grey-shaded area represents the combined effect of harm reduction (including NDP and OAT) and ART (Scenario S1) * indicates baseline ART efficacy assumption in reducing HIV transmission via needle sharing.

Figure 3. Sensitivity analysis on the percentage of incident cases averted among PLHIV and HIV-positive PWID 1996–2013, attributable to ART and harm reduction services at 50% ART efficacy

Panel A: One-way sensitivity analysis on the effect of harm reduction services among PLHIV Panel B: One-way sensitivity analysis on the effect of ART among PLHIV PLHIV: people living with HIV/AIDS; PWID: people who inject drugs. UB: upper bound of the sensitivity scenario range; LB: lower bound of the sensitivity scenario range. * Where observed data was available for both OAT and needle distribution services. ^†77% = 2473/3204 = (S4-S2)/(S4-S1); ^‡44% = 1409/3204 = (S4-S3)/(S4-S1).

Figure 3. Sensitivity analysis on the percentage of incident cases averted among PLHIV and HIV-positive PWID 1996–2013, attributable to ART and harm reduction services at 50% ART efficacy

Panel A: One-way sensitivity analysis on the effect of harm reduction services among PLHIV Panel B: One-way sensitivity analysis on the effect of ART among PLHIV PLHIV: people living with HIV/AIDS; PWID: people who inject drugs. UB: upper bound of the sensitivity scenario range; LB: lower bound of the sensitivity scenario range. * Where observed data was available for both OAT and needle distribution services. ^†77% = 2473/3204 = (S4-S2)/(S4-S1); ^‡44% = 1409/3204 = (S4-S3)/(S4-S1).