Comparison of Second Generation Molecular Assays for Chlamydia Trachomatis in Female Urines and Self-Collected Vaginal Swabs

Background:  Less invasive screening samples such as self-collected vaginal swabs (SCVS) and first catch urine (FCU) are suitable for C. trachomatis testing in second generation molecular assays on automated instruments. The objectives were to test FCU and four SCVS from women.

Methods:  From July 2012 to August 2013, 575 women self-collected FCU and four SCVS using collection kits from Abbott Molecular RealTime CT/NG, Becton Dickinson BD ProbeTec ET CT/GC Q^X, Roche Diagnostics cobas 4800 CT/NG and Hologic/GenProbe Aptima Combo 2 (AC2). A proportion of each sample was spiked with known concentrations of C. trachomatis to detect inhibitors. A patient infected status of two positive tests for a sample type or two different samples positive in a single test were used for comparisons.

Results:  The analytical sensitivity of AC2 assay was 10-100 fold more sensitive than the other tests. There was no inhibition in either specimen type for all assays. The clinical sensitivities for SCVS were 96.3% for AC2 on both TIGRIS and PANTHER, 96.2% for m2000, 88.9% for ProbeTec ET Q^X on a Viper instrument and 83.0% for cobas 4800. For FVU testing, clinical sensitivity of AC2 was 95.9% on TIGRIS and 95.8% on PANTHER, 79.6% for m2000, 80.0% for ProbeTec Q^Xon Viper and 86.0% for cobas 4800. All assays demonstrated specificities above 99%.

Conclusions:  Inhibitors of amplification did not impact on the sensitivity of the second generation assays in SCVS and FCU. AC2 and RealTime assays were more sensitive than ProbeTec ET Q^X and cobas 4800 tests on SCVS whereas the AC2 assay which detects C. trachomatis rRNA was considerably more sensitive than the three DNA tests on FCU. The clinical sensitivities observed in this head to head study are likely determined by analytical sensitivity and the concentration of target analytes in clinical samples.