Treponema pallidum PCR screening at mucosal sites of asymptomatic men who have sex with men taking HIV pre-exposure prophylaxis

Early detection and treatment of syphilis will reduce the infectious period and transmission. We aimed to determine whether screening men who have sex with men (MSM) taking HIV pre-exposure prophylaxis (PrEP) for syphilis using Treponema pallidum polymerase chain reaction (PCR) could detect syphilis before the appearance of syphilis antibodies in serology. MSM attending 3-monthly PrEP clinic visits in Melbourne, Australia, were screened with a PCR assay targeting the polA gene of T. pallidum from an anal swab and an oral rinse between November 2019 and March 2020. Participants were serologically screened for syphilis using chemiluminescence immunoassay. A total of 309 asymptomatic participants provided an anal swab and oral rinse sample for T. pallidum PCR screening. Two syphilis cases (0.6%) were detected: one man had a positive serology only; another man had T. pallidum detected by PCR from an anal swab and a positive serology. PCR positivity was 0.3% (n = 1) for anal swabs and 0% (n = 0) for oral rinse. In this study, T. pallidum PCR screening at routine PrEP clinic visits did not identify additional cases of early syphilis over serological screening performed at these visits.