GeneXpert MTB/RIF as a Rapid Diagnostic tool for Diagnosis of Pulmonary, Extra-pulmonary Tuberculosis and Rifampicin Resistance in the Egyptian Population

Rapid and accurate detection of Mycobacterium tuberculosis complex (MTBC) with early detection of drug-resistance is mandatory for the effective control of TB.

Aim: An evaluation of the performance of the GeneXpert MTB/RIF assay in the diagnosis of pulmonary and extra-pulmonary TB and Rifampicin (RIF) resistance.

Materials and Methods: 420 patients with clinical or radiological suspicion of Tuberculosis were included in this study. GeneXpert MTB/RIF (Cepheid, Sunnyvale, USA) was used for diagnosis of pulmonary, extra-pulmonary tuberculosis and Rifampicin-resistance. Comparison of our results was done with the results of acid-fast bacilli (AFB) smear microscopy and the culture method (as a standard method). Rifampicin resistance results were compared to drug susceptibility testing (DST) as a gold standard method. Sequencing of the rpoB gene was done for the Rifampicin-resistant isolates using genetic analyser ABI prism 3130 XL (Applied Biosystems, USA).

Results: TB was diagnosed in 23.7% of patients suspected to have pulmonary TB and in 12.5% of patients suspected of having extra-pulmonary TB. The GeneXpert MTB/RIF detected MTB with an overall sensitivity of 88.7% (63/71), specificity of 97.8% (224/229), PPV of 92.6% and NPV of 96.5%. There was a highly statistically significant difference between GeneXpert MTB/RIF and AFB smear microscopy, in pulmonary and extra-pulmonary cases. RIF resistance was identified by DST in 2.3% (2/86) TB culture positive specimens; both of which were multidrug-resistant (MDR). The GeneXpert MTB/RIF assay showed RIF resistance in all specimens identified as RIF resistant by DST in addition to one specimen identified as RIF susceptible by DST. The results of gene sequencing were in concordance with that obtained from GeneXpert MTB/RIF.

Conclusions: Our findings inforce the use of GeneXpert MTB/RIF as a prompt rapid diagnostic tool for early diagnosis of pulmonary TB especially in smear-negative and extra-pulmonary tuberculosis with the early detection of Rifampicin resistance.