EVALUATION OF A NEW MOLECULAR DIAGNOSTIC PLATFORM FOR TUBERCULOSIS: DETECTION OF RESISTANCE TO ISONIAZID AND RIFAMPICIN

Tuberculosis (TB) is an infectious disease whose main etiological agent in humans is Mycobacterium tuberculosis . Resistance to the main antimicrobials used in first-line treatment ‒ Rifampicin (RIF) and Isoniazid (INH) ‒ must be detected early to enable appropriate treatment and prevent transmission of resistant strains. The Xpert® MTB-RIF Ultra (a molecular test for identification of M. tuberculosis and resistance to RIF [RIFr]) increases TB case detection rates and potential RIFr detection. It is a rapid test, providing results within up to 2-hours with high accuracy. However, it has the disadvantage of high per-test and equipment costs. In addition, this platform, in its basic version adopted by the Brazilian TB Control Program, does not detect resistance to INH (INHr), which generally precedes RIFr and is, in fact, an early and accurate marker of risk for selecting an MDR strain ( M. tuberculosis INHr and RIFr simultaneously). In recent years, several automated platforms with molecular detection of M. tuberculosis and resistance have been developed. This study aimed to evaluate the accuracy of the STANDARD® M10 platform for detection of RIFr and INHr. To evaluate the accuracy of the STANDARD® M10 platform and its agreement with Xpert® MTB-RIF Ultra, a panel of strains previously characterized molecularly and phenotypically was used. The inoculum from 7H9 culture was standardized using the McFarland scale (0.5) and mixed 1:2 with a proprietary solution provided by the manufacturer, then loaded into cartridges for both platforms. A total of 39 strains were analyzed: 59% MDR, 8% mono-RIFr, 8% mono-INHr, and 26% pansusceptible. Statistical analysis showed a Kappa coefficient of 92%, indicating high agreement between the tests. It should be noted that the four discordant samples were MDR strains with a 12 bp insertion in the rpoB gene (435D>435DQNNP). Preliminary results show high levels of accuracy and agreement for the STANDARD® M10 platform. Expanding the portfolio of diagnostic tests for TB strengthens TB control programs; however, clinical trials prior to the introduction of new technologies are essential to support incorporation of this new platform into the Brazilian Unified Health System.