Factors Associated with Syphilis Transmission and Acquisition Among Men Who Have Sex with Men (MSM) in 3 U.S Cities: Protocol for the Network Epidemiology of Syphilis Transmission Study (NEST) (Preprint)

BACKGROUND In the United States, primary and secondary syphilis rates have increased more rapidly among men who have sex with men (MSM) than any other subpopulation. Rising syphilis rates among MSM reflect changes in both individual behaviors and the role of sexual networks (e.g., persons linked directly or indirectly by sexual contact) in infection spread. Decades of research examined how sexual networks influence sexually transmitted infections (STIs) among MSM; however, few longitudinal data sources focused on syphilis have collected network characteristics. The Centers for Disease Control and Prevention, in collaboration with three sites, enrolled a prospective cohort of MSM in three U.S. cities to longitudinally study sexual behaviors and STIs, including HIV, for up to 24 months. OBJECTIVE The Network Epidemiology of Syphilis Transmission Study (NEST) collected data on factors related to syphilis transmission and acquisition among MSM. METHODS The NEST study was a prospective cohort study that enrolled 748 MSM in Baltimore, MD, Chicago, IL, and Columbus, OH. NEST recruitment employed a combination of convenience sampling, venue-based recruitment, and respondent-driven sampling approaches. At quarterly visits, participants completed a behavioral questionnaire and tested for syphilis, HIV, gonorrhea and chlamydia. Participants also provided a list of their sexual partners and described their three most recent partners in greater detail. RESULTS NEST participants enrolled in the study from July 2018 to December 2021. At baseline, the mean age of participants was 31.5 years (standard deviation (SD): 9.1). Over half of participants were non-Hispanic Black (54.4%), 29.8% were non-Hispanic White, and 8.8% were Hispanic or Latino. Multiple recruitment strategies across the three study locations, including respondent-driven sampling, clinic referrals, flyers and social media advertisements, strengthened NEST participation. Upon completion of follow-up visits in March 2022, the mean number of visits completed was 5.1 (SD: 3.2; range = 1–9) in Baltimore, 2.2 in Chicago (SD: 1.6, range 1–8), and 7.2 (SD: 2.9; range = 1–9) in Columbus. Using a community-based participatory research approach, site-specific staff were able to draw upon collaborations with local communities to address stigma concerning STIs, particularly syphilis, among potential NEST participants. Community-led efforts also provided a forum for staff to describe NEST study objectives and plans for research dissemination to the target audience. Strategies to bolster data collection during COVID-19 included telehealth visits (all sites) and adaptation to STI specimen self-collection (Baltimore only). CONCLUSIONS Data from NEST will be used to address important questions regarding individual and partnership-based sexual risk behaviors among MSM, with the goal of informing interventions to prevent syphilis in high burden areas.