BackgroundDrug-resistant tuberculosis, especially multidrug-resistant tuberculosis (MDR-TB), is a major public health problem. Effective management of MDR-TB relies on accurate and rapid diagnosis. In this study, we assessed the diagnostic accuracy of the Genotype MTBDRplus assay in diagnosing MDR-TB in Cameroon, and then discuss on its utility within the diagnostic algorithm for MDR-TB.MethodsIn this cross-sectional study, 225 isolates of Mycobacterium tuberculosis cultured from sputum samples collected from new and previously treated pulmonary tuberculosis patients in Cameroon were used to determine the accuracy of the Genotype MTBDRplus assay. We compared the results of the Genotype MTBDRplus assay with those from the automated liquid culture BACTEC MGIT 960 SIRE system for sensitivity, specificity, and degree of agreement. The pattern of mutations associated with resistance to RIF and INH were also analyzed.ResultsThe Genotype MTBDRplus assay correctly identified Rifampicin (RIF) resistance in 48/49 isolates (sensitivity, 98% [CI, 89%–100%]), Isoniazid (INH) resistance in 55/60 isolates (sensitivity 92% [CI, 82%–96%]), and MDR-TB in 46/49 (sensitivity, 94% [CI, 83%–98%]). The specificity for the detection of RIF-resistant and MDR-TB cases was 100% (CI, 98%–100%), while that of INH resistance was 99% (CI, 97%–100%). The agreement between the two tests for the detection of MDR-TB was very good (Kappa = 0.96 [CI, 0.92–1.00]). Among the 3 missed MDR-TB cases, the Genotype MTBDRplus assay classified two samples as RIF-monoresistant and one as INH monoresistant.The most frequent mutations detected by the Genotype MTBDRplus assay was the rpoB S531 L MUT3 41/49 (84%) in RIF-resistant isolates, and the KatG S315 T1 (MUT1) 35/55 (64%) and inhA C15T (MUT1) 20/55 (36%) mutations in INH-resistant isolates.ConclusionThe Genotype MTBDRplus assay had good accuracy and could be used for the diagnosis of MDR-TB in Cameroon. For routine MDR-TB diagnosis, this assay could be used for Mycobacterium tuberculosis cultures containing contaminants, to complement culture-based drug susceptibility testing or to determine drug resistant mutations.

The recommendation of the Genotype MTBDRplus assay to assume rifampicin resistance based solely on failure to hybridize to rpoB wild-type probe allows the identification of important RIF-resistant isolates. About 20% (3/15) of such isolates could be missed by relying only on the standard MGIT 960 DST assay for drug susceptibility testing.