Assessment of the Genexpert MTB/RIF Assay's Performance for the Quick Identification of Rifampicin-Resistant Mycobacterium Tuberculosis

Introduction: Tuberculosis (TB) remains a global health crisis, and the emergence of rifampicin-resistant TB (RR-TB) has further escalated this challenge. The speed and accuracy of diagnosis are critical for the timely treatment of the disease. Objective: The purpose of this study was to evaluate the diagnostic performance of the GeneXpert MTB/RIF assay in identifying MTB and rifampicin resistance, in an effort to enhance the diagnosis and treatment of tuberculosis (TB).Materials and Methods: This cross-sectional study was conducted at the National Tuberculosis Institute (NTI)/National Reference Laboratory (NRL) for Tuberculosis in Baghdad from February to September 2021. Morning sputum samples were collected from consenting patients. These samples were analyzed using Ziehl-Neelsen staining microscopy, the Xpert MTB/RIF assay, and culture on Löwenstein-Jensen (LJ) medium. Results: Among 140 suspected TB patients, 60 were confirmed to have active pulmonary tuberculosis (ATB) based on at least one positive microbiological test result, including acid-fast bacilli (AFB) staining, bacterial culture, molecular testing (Xpert MTB/RIF), clinical symptoms, and chest radiography (CXR) indicative of TB. Out of the 140 sputum specimens, 38 (27.14%) were positive by ZN/AFB smear microscopy, 60 (42.86%) by the GeneXpert MTB/RIF assay, and 41 (29.28%) by MTB culture on LJ medium. With respect to the detection of bacillary load, out of the sixty specimens that tested positive for bacillary load, the semi-quantitative results showed that 11 samples (18.3%) had high results (mean cycle threshold (CT) value =14.3), 25 (41.7%) had medium results (mean CT value =20.8), 15 (25.0%) had low results (mean CT value = 25.4), and 9 (15.0%) had very low results (mean CT value =30.1).Rifampicin resistance was detected in 7 out of 60 (11.67%) of the MTB-positive specimens, while 53 (88.33%) showed no rifampicin resistance (Rif-S).

Conclusion: The GeneXpert MTB/RIF assay demonstrates high sensitivity and specificity, making it a valuable diagnostic tool for the rapid detection of TB bacilli and the simultaneous identification of RR-TB. Early detection of rifampicin resistance is crucial in curbing the spread of multidrug-resistant TB (MDR-TB) strains.