O06.1 Oral and anal Treponema pallidum detection in men who have sex with men with early infectious syphilis: a cross-sectional study

Background While syphilis transmission is increasing, precisely how Treponema pallidum is transmitted sexually is unclear. This study of MSM with early syphilis determined the frequency of Treponema pallidum shedding from potentially asymptomatic sites and the stage with the most frequent shedding. Methods MSM were recruited between 2015 and 2019, at Melbourne Sexual Health Centre, Australia. Men were eligible if they reported sex with men during the previous year, were aged ≥18 years and had laboratory-confirmed primary, secondary, or early latent syphilis. All syphilis lesions were swabbed. Non-lesion samples collected were oral rinse, oral cavity swab, anal canal swab, urine, and semen. Specimens were tested for T. pallidum using two PCR assays. Results 200 men with serologically-confirmed early syphilis were included: 54 (27%) primary, 93 (46·5%) secondary and 53 (26·5%) early latent cases. T. pallidum DNA was detected orally in 48 (24%; 95% CI: 18.3–30.5%) men by oral rinse and/or oral lesion swab, 24 with no oral lesion. Oral T. pallidum detection was most frequent during secondary syphilis compared to other stages, (44%(41/93) versus 7% (7/107), p Conclusion Unrecognised oral and anal shedding of T. pallidum may be a factor in sustaining syphilis transmission. Secondary syphilis may be the most infectious stage, with oral transmission possibly being important. Earlier detection and treatment for syphilis to prevent progression to the secondary stage may improve syphilis control.