This work was presented at the Feb 2017 Conference of Retroviruses and Opportunistic Infections (CROI) in Seattle, Washington.
Background: Men who have sex with men (MSM) continue to experience high HIV incidence in the United States. Sexual role, partnership types, infection stage, and care engagement strongly determine HIV transmission rates within serodiscordant MSM partnerships. Estimating the distribution of transmissions by these factors is critical to targeting prevention efforts. Previous studies to estimate the distribution of transmissions by these factors have yielded conflicting results and significant debate, likely due to heterogeneous populations and methods. We assessed all factors in one comprehensive US-based model in order to provide internally-consistent and actionable estimates.
Methods: A mathematical model simulated HIV transmission dynamics within sexual partnership networks of US MSM over a 10-year period. Parameters were estimated from HIV cohorts in Atlanta and national behavioral and clinical literature. We estimated population attributable fractions (PAFs) and 95% credible intervals by network and behavioral factors within partnerships and clinical status of the infected partner.
Results: Among all incident HIV infections, 42% occurred in main partnerships, 48% in casual partnerships, and 10% in one-time partnerships. Three-quarters (75%) of transmissions were to the receptive AI partner. One in five transmissions (21%) originated from an acute-stage partner, 60% from a non-AIDS chronic-stage partner, and 19% from a partner who progressed to AIDS. Nearly all infections resulted from AI with an infected partner who was undiagnosed (31%) or who was not retained in care (61%); few infections occurred during time on ART with partial (5%) or full (1%) viral suppression.
Conclusion: Our model suggests two high-value targets for prevention: MSM in non-main partnerships and in partnerships in which the infected partner has fallen out of HIV care. Assessing risk behavior specific to partnership type remains necessary to tailoring the delivery of HIV prevention tools. Targeting strategies may emphasize PrEP for HIV-negative MSM in non-main partnerships as partners' HIV status or care engagement may be unknown. Within main serodiscordant partnerships, strategies may include PrEP for the HIV-negative partner and support for the HIV-positive partner to remain effectively engaged in care. Because HIV-positive men not retained in care contribute the majority of ongoing HIV transmissions, efforts to engage these men individually and through their partnerships will be challenging but essential.
Check out the poster below!
Downloadable Files:CROI 2017 Poster_ Bardales.pdf