Causal Effects of Stochastic PrEP Interventions on HIV Incidence Among Men Who Have Sex With Men

Abstract

Antiretroviral preexposure prophylaxis (PrEP) is highly effective in preventing human immunodeficiency virus (HIV) infection, but uptake has been limited and inequitable. Although interventions to increase PrEP uptake are being evaluated in clinical trials among men who have sex with men (MSM), those trials cannot evaluate effects on HIV incidence. Estimates from observational studies of the causal effects of PrEP-uptake interventions on HIV incidence can inform decisions about intervention scale-up. We used longitudinal electronic health record data from HIV-negative MSM accessing care at Fenway Health, a community health center in Boston, Massachusetts, from January 2012 through February 2018, with 2 years of follow-up. We considered stochastic interventions that increased the chance of initiating PrEP in several high-priority subgroups. We estimated the effects of these interventions on population-level HIV incidence using a novel inverse-probability weighted estimator of the generalized g-formula, adjusting for baseline and time-varying confounders. Our results suggest that even modest increases in PrEP initiation in high-priority subgroups of MSM could meaningfully reduce HIV incidence in the overall population of MSM. Interventions tailored to Black and Latino MSM should be prioritized to maximize equity and impact.

Keywords: HIV; causal inference; inverse probability weighting; men who have sex with men; preexposure prophylaxis; stochastic interventions.

Figure 1

Estimated effects of interventions that increase the propensity score (hazard) for initiating preexposure prophylaxis (PrEP) by in high-priority subgroups of men who have sex with men (MSM) relative to the natural course, Fenway Health, Massachusetts, 2012–2018. A) Estimated increase in the 2-year cumulative proportion of the population initiating PrEP; B) estimated relative reduction in 2-year risk of incident human immunodeficiency virus (HIV) diagnosis. The error bars show the 95% nonparametric bootstrap confidence intervals (CIs) of the estimates. RRR, relative risk reduction.

Figure 2

Estimated relative reduction in 2-year human immunodeficiency virus (HIV) risk under a stochastic intervention that increases the propensity (hazard) of initiating preexposure prophylaxis (PrEP) by among Black or Latino men who have sex with men (MSM) with a recent health-care encounter at Fenway Health compared with the natural course, Massachusetts, 2012–2018. The shaded area represents 95% pointwise nonparametric bootstrap confidence bands of the estimates. The dashed lines relate to the intervention with the shift of specified in Figure 1.

Figure 3

Estimated 2-year human immunodeficiency virus (HIV) risk difference per 1,000 individuals over time under a stochastic intervention that increases the propensity of initiating preexposure prophylaxis (PrEP) by among Black or Latino men who have sex with men (MSM) with a recent health-care encounter at Fenway Health versus under observed PrEP initiation, or the natural course, Massachusetts, 2012–2018. The shaded area represents a 95% pointwise nonparametric bootstrap confidence band of the estimates.