A successful introduction to a non-expert setting of the thin-layer agar Colour Test as an indirect phenotypic drug susceptibility test for Mycobacterium tuberculosis.

Abstract Objectives We evaluated the performance of the MDR/XDR-TB Colour Test (CT) as an in-house thin-layer agar-based indirect drug susceptibility test (DST) in previously inexperienced settings in Estonia. Methods After a two-day hands-on training, six panels of 150 Mycobacterium tuberculosis isolates were cultured onto CT plates prepared in-house in two laboratories. Finally, triplicate readings of 900 CT plates resulted 18 DST patterns for each of the initial isolates. Time intervals to the results and for media preparations were estimated, as were intra- and interobserver agreements, test sensitivities and specificities calculated. BACTEC MGIT 960 DST was used as a reference. Results The median time to produce DST results for isoniazid, rifampicin and levofloxacin was 13 days. The CT sensitivity ranged from 94.7% for levofloxacin to 95.8% and 97.3% for isoniazid and rifampicin, respectively. The test specificities were even higher exceeding 97% for all three drugs tested. Interobserver agreement reached 100% in one of the laboratories and exceeded 97% for levofloxacin and 99% for isoniazid and rifampicin in the second laboratory. Conclusions The implementation of the CT into a new laboratory was straightforward with only minimal guidance. This study proves that the CT is highly reproducible and easily interpreted by previously inexperienced personnel.