Evaluation of GeneXpert MTB/RIF for the detection of Mycobacterium tuberculosis and resistance to rifampin in extra-pulmonary specimens

AbstractAims and objectivesThis study evaluated the performance of GeneXpert (GX) for direct detection of MTB in extra-pulmonary specimens and assessed the ability of the assay to detect resistance to RIF.Methods104 clinical samples from a tertiary hospital in Sfax, Tunisia were analyzed. Specimens were processed using GX, Ziehl Neelsen and auramine smear, conventional culture on LJ and MGIT 960 media, and drug phenotypic susceptibility testing on LJ and MGIT 960. The diagnosis was made based on clinical, radiological, microbiological, pathological and therapeutic criteria.ResultsIn total, 51 patients were considered tuberculous. The PCR result obtained in less than two hours was positive for 46 samples and rifampicin was sensitive to all these cases. The sensitivity, specificity, positive predictive value and negative predictive value of GX were 90%, 60.6%, 19.6% and 98.3% compared with direct examination, 84.8%, 74.6%, 60.9% and 91.4% compared with culture and 84.3%, 94.3%, 93.4%, 86.2% compared with final diagnosis. The sensitivity of the GXt was 86% in biopsies and 75% in pus, collections and in biological fluids.ConclusionThe GX is a simple, rapid technique for real-time PCR and has increased the sensitivity of detection of Mycobacterium tuberculosis complex. It must be part of the diagnostic arsenal of tuberculosis without replacing conventional microbiological tools and allow early diagnosis and appropriate treatment