HIV / STI
Mixing It Up: Age and Partnership Patterns in MSM Sexual Networks Brittany Liebhard* Brittany Liebhard Liebhard Liebhard Liebhard Liebhard The Ohio State University
Background: Syphilis, a sexually transmitted infection (STI) associated with significant morbidity if untreated, is transmitted within sexual networks. Structural characteristics of sexual networks, such as degree and age mixing patterns, are key drivers of transmission, yet are rarely quantified using empirical data. We examined these characteristics among men who have sex with men (MSM) to help understand syphilis transmission patterns.
Methods: We analyzed baseline egocentric sexual networks of men participating in the Network Epidemiology of Syphilis Transmission (NEST) study in Columbus, Ohio (2019-2021). Men reported all sexual partners from the preceding three months; analyses were restricted to male partners. We computed mean degree (average number of sexual partners), the proportion of age-discordant partnerships (partners in different age groups; see figure for groups) and the mean absolute age difference between men and their partners. We examined how network degree and age mixing varied by age and partnership type (main vs casual).
Results: Men (n=241) reported 1,023 male partnerships, for an overall mean of 4.2 partners per person (SD: 4.6, range: 0-25). Men reported substantially more casual (mean: 3.7, SD: 4.6, range: 0-24) than main partners (mean: 0.5, SD: 0.6, range: 0-4). Nearly three-quarters (70%) of all partnerships were age-discordant. The proportion discordant ranged from 44% among men aged 18–24 years up to 93% among men aged 40–44 years. Overall and by each age group, participants were closer in age to their main partners than their casual partners. We observed an age difference of 10 or more years with 16% of main partners and 28% of casual partners.
Conclusion: We observed substantial variation in degree and age mixing patterns by age and partnership type. Recent estimates of sexual network characteristics are essential for understanding current transmission dynamics and designing interventions to curb the syphilis epidemic.
