Monitoring therapy success of urogenital Chlamydia trachomatis infections in women: A prospective observational cohort study

INTRODUCTION The use of a nucleic acid amplification test (NAAT) as a test of cure after treatment is subject to discussion, as the presence of C. trachomatis nucleic acids after treatment may be prolonged and intermittent without presence of infectious bacteria. We used cell culture to assess if a positive RNA- or DNA-based NAAT after treatment indicates the presence of viable C. trachomatis. METHODS We included women with asymptomatic urogenital C. trachomatis infection visiting the Amsterdam STI clinic from September 2015 through June 2016. Endocervical swabs were collected prior to treatment with azithromycin, and during three follow-up visits 7, 21 and 49 days after treatment. Collected swabs were subjected to C. trachomatis culture and a RNA- and DNA-based NAAT. High-resolution multilocus sequence typing (hr-MLST) was used to further differentiate potential re-infections. RESULTS We included 90 women with a positive RNA-test prior to receiving treatment of whom 81 (90%) were also DNA-positive, and 69 (76.7%) culture-positive. Prolonged and intermittent positive RNA and DNA results over time were observed. Three women had culture positive results at the second visit, but all were negative at the third visit. Five women had NAAT-positive results at the fourth visit of whom three women were also culture-positive indicating a viable infection. All five women reported unprotected sexual contact since the first visit. From 2, hr-MLST sequence types were obtained. One had a different sequence type indicating a new infection the other was identical to the previously found indicating a potentially persisting infection. CONCLUSION Most RNA- or DNA-positive results after treatment of urogenital C. trachomatis may be caused by non-viable molecular remnants since they cannot be confirmed by culture. In a minority viable C. trachomatis was found in culture at the second visit, indicating that patients may remain infectious at least 7 days after treatment.