High levels of adherence are required to suppress levels of plasma HIV RNA [7], and incomplete adherence has been associated with virological rebound and the emergence of antiretroviral resistance [8]. The majority of research on adherence among IDUs has focused on individual-level barriers, including illicit drug use [9], lower self-efficacy [10, 11], and comorbid psychiatric conditions [12-14]; however, longer term trends in adherence among IDUs have not been well described.

Thus, the present study evaluated long-term adherence patterns among IDUs initiating ART between 1996 and 2009 in a setting of universal access to HIV care. Data for these analyses were collected through the AIDS Care Cohort to Evaluate Access to Survival Services (ACCESS), an ongoing community-recruited prospective cohort study of HIV-positive IDUs which has check details been described in detail previously [15, 16]. In brief, beginning in May 1996, participants were recruited through self-referral and street outreach from Vancouver’s Downtown Eastside, the local epicentre of drug-related transmission of HIV. At baseline and semi-annually, all HIV-positive participants provided blood samples

and completed an interviewer-administered questionnaire. The questionnaire elicits demographic data as well as information about participants’ drug use, including information about type of drug, frequency of drug use, involvement in drug treatment and periods of abstinence. All participants provide informed consent and are remunerated $CDN20 for each study visit. The study is somewhat unusual in that the province of British Columbia not only delivers all HIV care free of charge through the province’s universal healthcare Talazoparib system but also has a centralized HIV treatment registry. This allows for the confidential linkage of participant survey data to a complete prospective profile of all HIV-related clinical monitoring and antiretroviral Tacrolimus (FK506) dispensation records.

The Providence Health Care/University of British Columbia Research Ethics Board reviewed and approved the ACCESS study. Participants were eligible for the present analysis if they initiated ART between May 1996 and December 2009. The primary outcome in this study was adherence to ART based on a previously validated measure of prescription refill compliance [17, 18]. Specifically, using data from the centralized ART dispensary, we defined adherence as the number of days for which ART was dispensed over the number of days an individual was eligible for ART in the year after ART was initiated. This calculation was restricted to each patient’s first year on therapy to limit the potential for reverse causation that could occur among patients who cease ART after they have become too sick to take medication [19, 20]. We have previously shown this measure of adherence to reliably predict both virological suppression [21-23] and mortality [17, 18]. As in previous studies, adherence was dichotomized as ≥95% versus <95% [21, 23, 24].