Clearance of <i>Treponema pallidum</i> from oral and anal sites after treatment of secondary syphilis: results from a multi-centre, prospective, cross-sectional study.

Abstract

Syphilis is increasing worldwide, and secondary syphilis may represent its most infectious stage. Scarce data exist on <i>Treponema pallidum</i> clearance after treatment. We aimed to determine the frequency and load of <i>T. pallidum</i> mucosal shedding, and time to clearance following treatment of secondary syphilis. Men-who-have-sex-with-men (MSM) and transgender women with secondary syphilis were recruited from Australian clinics between January 27, 2023, and August 19, 2024. Oral, anal or genital lesions were swabbed, and non-lesion samples (blood, oral cavity and anal canal swabs were collected on the day of treatment (baseline). Non-lesion oral cavity and anal canal swabs were repeated 3, 7, 14 and 30 days post-treatment. <i>T. pallidum</i> bacterial load was determined by quantitative PCR. 78 cis-men and one trans-woman, who reported sex with men, were included. At baseline, <i>T. pallidum</i> was detected in the participants' oral cavity, anal canal and blood of 81% (64/79), 70% (55/79) and 24% (19/79), respectively. When detected at oral and anal sites, 22/64 (36%) had oral lesions and 31/55 (59%) had anal lesions, respectively. The median oral and anal bacterial loads decreased significantly from baseline to day 3, [cycle thresholds 35.7-37.7, (1.7-1.2 copies/μL), (p = 0.013), and 30.2-38.2 (3.3-1.0 copies/μL), (p < 0.001), respectively]. <i>T. pallidum</i> cleared from 99% (96/97) of non-lesion, paired samples from 58 participants by day 7, 95% confidence interval (94-100%). During secondary syphilis, most MSM had <i>T. pallidum</i> DNA detected in oral and anal mucosa. Bacterial load dropped markedly 3 days post-treatment and cleared in almost all samples by 7 days. Australian National Health and Medical Research Council.