Opioid substitution therapy is associated with decreased HIV transmission among people who inject drugs
- Correspondence to: Lynn E Fiellin
Yale Medical Group, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06510, USA;
Commentary on: 
Injection drug use (IDU), through the sharing of drug injection paraphernalia and concurrent sexual risk behaviours, continues to fuel the HIV epidemic.1 Approximately, 16 million individuals inject drugs globally, an estimated 3 million of whom are HIV infected, underscoring the need for effective intervention.1 Although opioid substitution therapy (OST) is an important component of HIV prevention,2 ,3 only 8 of 100 individuals globally with IDU receive OST.2 A recently completed systematic review by the Cochrane Collaborative concluded that OST leads to risk reduction and decreased HIV incidence.4 The review included studies with a high level of bias and variability and did not focus on estimating the effect of OST on HIV transmission among people with IDU.4
MacArthur and colleagues conducted a systematic review and meta-analysis of published and unpublished studies. A comprehensive search strategy included identifying studies through MEDLINE, EMBASE and PsychINFO (until October 2011) and the Cochrane Library (until 2011), with a review of relevant references evaluating the impact of OST on HIV incidence. They searched MEDLINE, EMBASE and PsychINFO (until May 2011) for cohort studies reporting HIV incidence among people with IDU, contacting the authors for unpublished data. Randomised controlled trials, prospective cohort studies and case-control studies evaluating HIV incidence among people with IDU and examining the impact of OST on HIV incidence in this population were included. Cross-sectional or serial cross-sectional and retrospective studies; those based on prison populations; or reporting less than two seroconversions were excluded. Two reviewers applied inclusion/exclusion criteria and conducted data extraction. Incidence rate ratios, ORs and HRs with corresponding 95% CI were determined. A random effects meta-analysis was performed based on pooled results from studies including data on HIV seroconversion, person-years of follow-up or OST exposure; or provided an effect estimate and 95% CI. Risks of bias and study heterogeneity were assessed.
The review included 12 published and 3 unpublished studies, with 1016 incident HIV infections over 26 738 person-years of follow-up; data from 9 of these studies were used in the meta-analysis. All studies included methadone maintenance treatment. In the random effects meta-analysis, OST was associated with reduced HIV transmission in the unadjusted model (rate ratio 0.46, 95% CI 0.32 to 0.67, p<0.001); this persisted in the adjusted models (rate ratio 0.60, 95% CI 0.42 to 0.85, p=0.004).
Although previous studies assessed the impact of OST on HIV risk,4 this study quantified the effect size, providing strong support for OST as an important intervention for decreasing HIV incidence. This study had limitations: (1) the generalisability to all individuals with IDU and who are receiving OST is unclear; (2) the authors did not adjust for important covariates, including underlying HIV prevalence, OST medication adherence and support services; (3) given the diversity of support across settings for people with IDU, these findings may not apply to particular countries; (4) no studies included buprenorphine, which is growing in use, and in some cases, exceeding methadone as OST5 and (5) the majority of studies occurred during the late 1990s to early 2000s, prior to the advent of more potent and widely accessible regimens. Given the expected associated decreases in community viral load over time, risk of HIV transmission has, probably, similarly decreased, potentially overestimating the effect size.
Despite these limitations, the paper complements and extends existing data,4 by seeking out results from unpublished studies and providing a quantitative analysis of the impact on OST specifically on HIV incidence. Understanding how these effects differ based on setting, types of services provided in the context of OST, type of OST and patient characteristics will be important for prioritising resources. These findings represent an important step towards promoting policies to increase OST globally for HIV prevention6 and improving health outcomes for people with IDU.