Clearance of Chlamydial Ribosomal RNA by APTIMA Combo 2® Testing in Women With Chlamydia Treated with Azithromycin C.A. Renault, 1 D.M. Israelski, 1 V. Levy, 2 B.K. Fujikawa, 2 T.A. Kellogg, 3 J.D. Klausner 3 1 Stanford University School of Medicine, Stanford, California, USA, 2 San Mateo Medical Center and Health Department, San Mateo, California, USA, 3 San Francisco Department of Public Health, San Francisco, California, USA The U.S. Centers for Disease Control and Prevention recommend that pregnant women treated for Chlamydia trachomatis (CT) wait at least 3 weeks before obtaining a test for cure. This recommendation is based on expert opinion, as the duration of CT detection following treatment is uncertain. Prior studies have demonstrated that DNA-based tests may remain positive for up to 2 weeks following treatment, and therefore are not suitable as a test-of-cure in this period. Transcription-mediated amplification (TMA) amplifies CT ribosomal RNA (rRNA) and has improved sensitivity compared to the DNA-based assays. The time to clearance of rRNA following treatment for chlamydial infection is unknown. Background STD Prevention and Control Services, SF Department of Public Health, 1360 Mission Street, Suite 401, San Francisco, CA Phone (415) Fax (415) Website: ISSTDR 2005 Methods Objective To determine the percentage of subjects with urogenital chlamydial infection who tested TMA (APTIMA Combo 2) negative at pre-determined timepoints following treatment, in order to evaluate TMA as a possible test-of-cure. We enrolled women with a CT positive urine screening test (APTIMA Combo 2 (Gen-Probe, Inc., San Diego, CA, USA)) at adolescent clinics in northern California. Subjects were confirmed to be CT positive using a TMA vaginal swab at a post-screening visit (day 0). Participants were treated with directly-observed azithromycin 1 gram by mouth and were instructed to self-collect a APTIMA vaginal swab on the day of treatment and on days 3, 7, 10 and 14 after treatment. We calculated the percentage of women with a negative APTIMA test result at each time point. Actual estimates of time to CT clearance were compared with predicted probabilities determined by simple linear regression. Women who failed to abstain from sexual intercourse during the 14-day follow-up period or who failed to provide all follow-up vaginal swabs were excluded from the analysis. Results Of the 115 women initially screened for CT, 61 had a confirmatory baseline CT APTIMA vaginal swab, reported abstinence and returned all 4 vaginal swabs. Of the 54 not included in the analysis, 19 were lost-to-follow-up, 17 were CT negative at baseline or 2 could not be CT confirmed, 4 did not return all the requested vaginal swabs, and 12 reported ongoing sexual activity. 50% were Latina, 23% Asian/PI, 13% black, 8% white and 5% mixed. 17 subjects (17.7% of 96 subjects available for follow-up) tested CT negative by APTIMA on day 0, suggesting spontaneous clearance of CT prior to treatment. Median time to spontaneous clearance of CT was 5 days (range 1-55 days). Of the 61 women analyzed, 48 (79%) tested CT negative by APTIMA 14 days following single-dose treatment with azithromycin. Predicted time to 100% CT clearance was 17 (95% CI 16, 18) days. Figure. Actual and predicted probabilities of CT clearance Conclusions After treatment with single-dose azithromycin, the percent of women with CT rRNA detected by APTIMA Combo 2 declined with time. Although 79% of our sample cleared CT by day 14, rRNA was still detectable in 21% of the women two weeks following treatment. APTIMA Combo 2 should not be used as a test-of-cure for CT in the 14-day period following treatment. When using highly sensitive assays for CT rRNA, at least 17 days should elapse before testing to evaluate response to treatment. Peninsula AIDS Research Center, 222 West 39th Avenue, San Mateo, California, USA Phone (650) Fax (650) ISSTDR 2009 Table. Participant characteristics (N=61) Median Age18 years Prior history of infection with Chlamydia trachomatis 33% Prior history of infection with Neisseria gonorrhoeae 8% Median number of male partners in the last 12 mos. 2 Condom use: Always/Almost always Sometimes Never 12% 64% 15%