Oral and anal detection of Treponema pallidum DNA among transgender women and travestis with high-titre syphilis in Brazil: findings from the MyTTrA study

Background Data on transgender women and travestis (TGW) concerning oral and anal detection of Treponema pallidum (TP) DNA are lacking. We aimed to estimate the prevalence of oral and anal TP DNA detection and the frequency of azithromycin resistance-associated mutations among TGW with high-titre syphilis in Brazil. Methods We conducted a nested cross-sectional study as part of the TransOdara study among TGW in five Brazilian cities. Participants with high-titre syphilis (reactive treponemal test and VDRL titre ≥1:8) and an analysable oral or anal specimen underwent quantitative PCR targeting the tpp47 and polA genes to detect TP DNA. TP DNA-positive specimens were further analysed using nested PCR and Sanger sequencing to identify mutations associated with azithromycin resistance. Findings Among the 249 participants with high-titre serological syphilis and analysable sample, TP DNA was detected in 25 (10.0%, 95% CI 6.6–14.5): 14 (5.6%) from the oral site only, 6 (2.4%) from the anal site only, and 5 (2.0%) from both sites. Participants in whom TP DNA was detected were younger and more frequently reported STI symptoms and anogenital ulcers during the preceding six months. The detection rate increased with VDRL titre (odds ratio 2.44, 95% CI 1.74–3.41 per doubling of titre for any oral or anal detection). Mutations associated with azithromycin resistance were observed in 76% (19/25, 95% CI 54.9–90.6) of participants in whom TP was detected. Interpretation TP DNA was detected in 10% of participants with high-titre serological syphilis. Detection increased with higher VDRL titres, supporting an association between higher non-treponemal titres and mucosal TP DNA detection. These findings support continued epidemiological and molecular surveillance of syphilis and of azithromycin resistance in transgender populations. They do not support site-specific PCR screening: syphilis diagnosis remains serological, and benzathine benzylpenicillin G remains the treatment of choice.