Dramatic shortening of the diagnosis of multidrug-resistant tuberculosis by the detection of rifampicin resistance using a genotypic method: GeneXpert MTB/RIF assay

Research paper by Ehab Badran Rakha, Heba Elshahawy

Indexed on: 29 Jan '18Published on: 27 Jan '18Published in: Comparative Clinical Pathology


In spite of all the evolutions in medicine, tuberculosis (TB) continues to be a terrifying contagious disease. In addition, the rise of multidrug-resistant TB (MDR-TB) is considered as a thorny problem that has greatly hindered the efforts of TB control. The classical drug susceptibility testing (DST) is the reference technique, but it takes many weeks for the identification of TB and MDR-TB. On the other hand, GeneXpert Mycobacterium tuberculosis (MTB)/rifampicin (RIF) has dramatically shortened the identification of both MTB and RIF resistance from weeks to only 2 h leading to a great breakthrough in the modern medicine. The aim of this study is to assess the use of GeneXpert assay for accelerating the diagnosis of MDR-TB in comparison to phenotypic DST by MGIT960 as the reference method. A total of 81 confirmed TB cases by both MGIT960 culture and GeneXpert were included in the current study. All sputum samples were processed for the detection of MDR-TB by both GeneXpert MTB/RIF assay and classical first-line DST method on MGIT960. Among studied TB cases, one rifampicin (RIF) monoresistance (1.2%), two isoniazid (INH) monoresistance (2.4%), and four (4.9%) MDR-TB (resistance to both RIF and INH) were identified by phenotypic methods. A significant statistical difference was found between RIF monoresistance and MDR-TB (P value < 0.01). GeneXpert identified six RIF-resistant cases, of which five cases were proven to be resistant to RIF by phenotypic DST using MGIT960. Furthermore, out of these five RIF-resistant cases, four cases were also resistant to INH, i.e., MDR-TB cases. The discrepancy between GeneXpert MTB/RIF and traditional DST for the detection of RIF resistance is not significant (P > 0.05). The sensitivity, specificity, negative, and positive predictive value of GeneXpert assay for identification of rifampicin resistance compared to DST as a reference method were 100, 98.7, 100, and 83.3%, respectively. It was concluded that the results of GeneXpert MTB/RIF and the standard phenotypic DST on MGIT960 for detection of RIF resistance were nearly the same regarding the sensitivity and specificity. Moreover, GeneXpert MTB/RIF was superior to DST on MGIT960 owing to its ability to dramatically shorten the period of MDR-TB diagnosis from weeks to only 2 h with fewer biohazard risks. Resistance to RIF could be used as a good foreteller for MDR-TB as most of RIF resistance are accompanied with isoniazid resistance.

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