The Centers for Disease Control and Prevention recommends treating latent syphilis of late/unknown duration (LSUD) with 3 doses of intramuscular benzathine penicillin G (BPG) or 28 days of oral doxycycline. This recommendation lacks high-quality evidence.
Methods
Using public health surveillance data from King County, Washington, we conducted a retrospective cohort study comparing rates of serological cure (≥2-titer reactive plasma reagin [RPR] decline) among persons with LSUD following receipt of 1 of 3 regimens: 1 dose of BPG, 3 doses of BPG, and 28 days of doxycycline. Subjects included persons diagnosed in 2007 to 2020 with an initial RPR ≥1:2 and follow-up RPR testing 1 to 36 months after treatment. We stratified initial RPRs into high and low titer (≥1:32,