Digital Anorectal Examination to Self-detect Primary Syphilis: A Prospective Cohort Study

Primary anorectal syphilis may go unnoticed in men who have sex with men (MSM) engaging in receptive anal sex. This study examined whether weekly digital anorectal examination (DARE) could help men self-detect abnormalities indicative of primary anorectal syphilis.

A cohort study of MSM aged ≥18 years who engage in receptive anal sex was conducted at the Melbourne Sexual Health Centre from 9 March 2022 to 4 August 2023. Participants received instructions on how to perform DARE, along with weekly text reminders for 48 weeks. Those who self-detected abnormalities were advised to seek clinical consultation. The primary outcome was the proportion of syphilis cases detected via DARE. Secondary outcomes included reports of DARE-related abnormalities, adherence, and experiences.

Of the 222 men recruited, six men (2.7%; 95% CI: 1.0-5.8) were diagnosed with syphilis-1 primary anorectal infection detected by DARE, 2 secondary infections, and 3 early latent syphilis infections. There were 32 clinical consultations prompted by DARE. On average, men performed 78.2% (95% CI: 77.3-79.0) of their weekly DARE which showed no significant variation over time (Ptrend = 0.26). Most found DARE easy to perform (>95.0%) and would continue performing it if recommended for early syphilis detection (77.6%).

Men's high adherence to performing we DARE suggests that it may complement routine screening for primary anorectal syphilis. However, its sensitivity may be limited, as 5 of 6 early syphilis cases did not have primary lesions that were self-detected by the 5 men.