Introduction Endemic rates of STIs like GC/CT and syphilis in Peru are only partially explained by individual behavioural or biological factors. Characterisation of sexual networks of MSM/TW with syphilis and/or GC/CT can provide critical data to inform prevention efforts.

Methods We enrolled 917 MSM/TW as screening for 2 STI control trials in Lima, Peru. We surveyed demographics and sexual identity, role, and 30 day network characteristics (number/gender of sexual partners, partner types, and frequency of anal/vaginal intercourse) and tested for syphilis (RPR >1:16) and oral, rectal, or urethral GC/CT (TMA). Differences in egocentric network characteristics were analysed with Chi-square and Kruskal-Wallis tests.

Results Approximately 38.7% (n=355) of subjects had a new STI diagnosis (Syphilis: 97 [10.6%]; GC/CT: 161 [17.6%]; Syphilis-GC/CT Co-infection: 49 [5.3%]). MSM/TW with GC/CT were younger (median age+IQR: 25 [22-30]) than those with syphilis (28 [23-34]) or no STI (28 [24-35]). STI-negative subjects were more likely to identify their sexual role as activo (insertive; 24.8%) than men with syphilis (10.8%) or GC/CT (14.7%). MSM/TW with GC/CT reported greater median numbers of all partners (3 [2-5]) and of casual male or transgender partners (2 [0–4]) than those with syphilis (2 [1-5] and 1 [0–2], respectively) or no STI (2 [1-3] and 1 [0–2]). Both GC/CT and syphilis were associated with the number of partnerships involving receptive anal intercourse (RAI; 2 [1-4] and 2 [1-13]) compared with STI-uninfected subjects (1 [0–2]). No differences were noted in the number of partnerships with condomless RAI or number of female partners.

Conclusion Egocentric network characteristics of MSM/TW with GC/CT and/or syphilis demonstrated progressive increases in network size, number of casual partners, and frequency of RAI when comparing no infection vs. syphilis vs. GC/CT +/- syphilis co-infection. Detailed understanding of network patterns, along with individual and partnership characteristics, will inform public health responses to HIV/STIs among Latin American MS.