Protocol for an evaluation of adherence monitoring and support interventions among people initiating antiretroviral therapy in Cape Town, South Africa—a multiphase optimization strategy (MOST) approach using a fractional factorial design

BACKGROUND: South Africa bears a large HIV burden with 7.8 million people with HIV (PWH). However, due to suboptimal antiretroviral therapy (ART) adherence and retention in care, only 66% of PWH in South Africa are virally suppressed. Standard care only allows for suboptimal adherence detection when routine testing indicates unsuppressed virus. Several adherence interventions are known to improve HIV outcomes, yet few are implemented in routinely due to the resources required. Therefore, determining scalable evidence-based adherence support interventions for resource-limited settings (RLS) is a priority. The multiphase optimization strategy (MOST) framework allows for simultaneous evaluation of multiple intervention components and their interactions. We propose to use MOST to identify the intervention combination with the highest levels of efficacy and cost-effectiveness that is feasible and acceptable in primary care clinics in Cape Town. METHODS: We will employ a fractional factorial design to identify the most promising intervention components for inclusion in a multi-component intervention package to be tested in a future randomized controlled trial. We will recruit 512 participants initiating ART between March 2022 and February 2024 in three Cape Town clinics and evaluate acceptability, feasibility, and cost-effectiveness of intervention combinations. Participants will be randomized to one of 16 conditions with different combinations of three adherence monitoring components: rapid outreach following (1) unsuppressed virus, (2) missed pharmacy refill collection, and/or (3) missed doses as detected by an electronic adherence monitoring device; and two adherence support components: (1) weekly check-in texts and (2) enhanced peer support. We will assess viral suppression (<50 copies/mL) at 24 months as the primary outcome; acceptability, feasibility, fidelity, and other implementation outcomes; and cost-effectiveness. We will use logistic regression models to estimate intervention effects with an intention-to-treat approach, employ descriptive statistics to assess implementation outcomes, and determine an optimal intervention package. DISCUSSION: To our knowledge, ours will be the first study to use the MOST framework to determine the most effective combination of HIV adherence monitoring and support intervention components for implementation in clinics in a RLS. Our findings will provide direction for pragmatic, ongoing adherence support that will be key to ending the HIV epidemic. TRIAL REGISTRATION: ClinicalTrials.gov NCT05040841. Registered on 10 September 2021. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13063-023-07322-z.