National HIV Prevention Conference | 2015
Background: Daily oral pre-exposure prophylaxis (PrEP) with tenofovir disoproxil fumarate and emtricitabine has proven effective to prevent HIV-1 infection among men who have sex with men (MSM) within clinical trial settings, but the population-level impact of this new technology will depend on eligibility and targeting policies, prescription coverage levels, and individual drug uptake and adherence. CDC guidance for MSM indicates PrEP for those with risk behaviors like high partnership acquisition rates. No studies have forecasted the population-level reductions in disease incidence according to these guidelines. There is a particular need to models outcomes among MSM subpopulations like young black MSM experiencing the highest disease burden.
Methods: As part of a CDC/NCHHSTP-funded modeling cooperative agreement begun in 2015 (the CAMP project), with final results for this phase completed in September 2015, this study extended stochastic models of HIV transmission dynamics in a population of young MSM in Atlanta, parameterized from prospective cohort and cross-sectional sexual-network studies in Atlanta. Our models incorporate temporally evolving sexual networks, using the statistical framework of exponential random graph models. Baseline models, calibrated to observed HIV prevalence in the target population, simulated the disease trajectories in the absence of PrEP. Counterfactual models then tested CDC indications for PrEP use, including sexual activity in the context of non-monogamous partnerships, unprotected anal sex, and serodiscordant partnerships. Relative infections averted and number needed to treat to prevent one infection were estimated for each guidance element under various levels of coverage driven by interventions that increased PrEP access and uptake.
Results: Early iterations of our models replicated the disease trajectories of HIV among young MSM in our target population. Development of PrEP modules for uptake and adherence was based on contributions from academic, CDC, and local health department partners in the CAMP project. Full results will present the epidemiological analyses on PrEP specified above to demonstrate the impact of CDC guidance and coverage interventions on reducing disease burden.
Conclusions/Implications: Estimating infections averted from adopting elements of CDC’s PrEP guidelines, alone and in combination, among various MSM populations will help to optimize risk-based screening in clinical settings. Mathematical modeling is a useful approach to investigating the complex interactions between behavioral and biological elements underlying these eligibility criteria. We expect that our model will indicate demographic elements related to the sexual network structure, such as the race and age of individuals within sexual partnerships, to be candidates for incorporation within guidance. Future work will extend these models by incorporating event-based PrEP dosage and implications for STI co-infections.