Time to clearance of Chlamydia trachomatis RNA and DNA after treatment in patients coinfected with Neisseria gonorrhoeae - a prospective cohort study

Background: Performing a test of cure (TOC) could demonstrate success or failure of antimicrobial treatment of Chlamydia trachomatis infection, but recommendations for the timing of a TOC using nucleic acid amplification tests (NAATs) are inconsistent. We assessed time to clearance of C. trachomatis after treatment, using modern RNA- and DNA-based NAATs. Methods: We analysed data from patients with a C. trachomatis and Neisseria gonorrhoeae coinfection who visited the STI Clinic Amsterdam, The Netherlands, from March through October 2014. After treatment with ceftriaxone plus either azithromycin or doxycycline, patients self-collected anal, vaginal or urine samples during 28 consecutive days. Samples were analysed using an RNA-based NAAT (Aptima Combo 2) and a DNA-based NAAT (Cobas 4800 CT/NG). We defined clearance as three consecutive negative results, and defined "blips" as isolated positive results following clearance. Results: We included 23 patients with C. trachomatis and N. gonorrhoeae coinfection. All patients cleared C. trachomatis during follow-up, and we observed no reinfections. The median time to clearance (range) was 7 days (1-13) for RNA, and 6 days (1-15) for DNA. Ninety-five per cent of patients cleared RNA at day 13, and DNA at day 14. The risk of a blip after clearance was 4.4 % (RNA) and 1.7 % (DNA). Conclusions: If a TOC for anogenital chlamydia is indicated, we recommend performing it at least 14 days after initiation of treatment, when using modern RNA-and DNA-based assays. A positive result shortly after 14 days probably indicates a blip, rather than a treatment failure or a reinfection.