Real-World Observations on the Diagnosis of Syphilis After Roll-out of Doxycycline Post-Exposure Prophylaxis

Doxycycline post-exposure prophylaxis (doxyPEP) is proven to prevent syphilis and other bacterial sexually transmitted infections among persons who were assigned male sex at birth (AMAB). Diagnosis of syphilis requires interpretation of rapid plasma regain (RPR) titers and clinical assessments; however, doxyPEP may affect RPR titers. We describe syphilis diagnosis at a public health clinic following roll-out of doxyPEP among AMAB persons. Syphilis diagnoses among AMAB prescribed doxyPEP significantly decreased (3.4% to 1.5%), while rates remained constant among persons with no doxyPEP prescription (3.4% to 3.0%). Clinical diagnoses, without confirmed laboratory syphilis, occurred frequently in the pre and post doxyPEP periods. No changes in the median RPR (1:16) were observed in the pre and post period among all AMAB persons, including when stratified by stage of syphilis, but median RPR titer was fourfold lower (1:4) in the nine cases among those prescribed doxyPEP.