Background: Repeat rectal STIs may be common in MSM using PrEP and could represent either treatment failure or re-infection. Retrospective cohort studies suggest that the efficacy of single-dose azithromycin may be lower than one week of doxycycline for rectal chlamydia. We assessed rates of repeat rectal gonorrhea and chlamydia infections in a prospective PrEP cohort study and compared rates of repeat chlamydia infection by treatment regimen.
Methods: The US PrEP Demonstration Project was an open label study of FTC/TDF PrEP that enrolled 557 MSM and transgender women. Participants were tested for STIs, including rectal gonorrhea and chlamydia, at screening and at weeks 12, 24, 36 and 48, and treated promptly if positive according to CDC guidelines. Participants who were diagnosed with rectal gonorrhea or rectal chlamydia at or after week 12 and who were positive for the same infection at the subsequent follow-up visit were considered to have a repeat infection.
Results: There were 91 episodes of rectal gonorrhea, 62 of which had a follow-up test at the next study visit; 4/62 (6%) were positive. Of 169 episodes of rectal chlamydia, 126 had a follow-up test. Of these, 111 were treated with azithromycin only, 10 with doxycycline only, and 3 with both; 2 were missing treatment information. Overall, 26/111 (23%) treated with azithromycin only and 2/10 (20%) treated with doxycycline only were positive for rectal chlamydia at the next visit (p=.6). All participants with repeat rectal gonorrhea and 82% of those with repeat rectal chlamydia reported having ≥1 episode of condomless receptive anal sex during the inter-visit interval.
Conclusions: In this PrEP cohort study, repeat rectal chlamydia infections were common, and did not vary by treatment regimen. Randomized controlled trials with a three week test of cure are needed to compare azithromycin vs. doxycycline for the treatment of rectal chlamydia.