Successful introduction of the Colour Test into inexperienced settings

Abstract

Implementation of non-commercial in-house methods into routine clinical diagnostics becomes more challenging, because these methods are not internationally standardized, most of the research in that field is underfunded and recommendations for their use is lacking. We conducted a study, where all the technicians were previously unfamiliar to the Colour Test (CT), a colorimetric redox indicator and thin-layer agar based Mycobacterium tuberculosis complex diagnosis and direct drug susceptibility testing (DST) method, and tested whether the performance of this in-house method is dependent on experience of the laboratory personnel. After a two-day hands-on training, six panels of 150 M. tuberculosis isolates were cultured onto CT plates prepared in-house by six technicians in two laboratories. Finally, triplicate readings of 900 CT plates resulted 18 DST patterns for each of the initial isolates. The results were compared to each other and the gold standard of BACTEC MGIT 960 DST results. The median time to produce M. tuberculosis CT DST results for three antituberculosis drugs was 13 days. The overall ability to correctly define phenotypic resistance 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. 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.