Genexpert MTB/RIF Assay: A Major Milestone for Diagnosing Mycobacterium Tuberculosis and Rifampicin-Resistant Cases in Pulmonary and Extra Pulmonary Specimens

Abstract

Background and objective: Tuberculosis is an endemic disease in Iraq. Many methods are available to diagnose pulmonary and extra pulmonary tuberculosis (TB). The most traditional test is the sputum smear for acid-fast bacilli (AFB). However, it is well known for its low sensitivity and specificity. On the other hand, culturing AFB although considered the gold standard for detecting mycobacterium Tuberculosis (MTB), yet it takes long time to confirm or exclude presence of TB. The WHO has recommended the use of a genebased molecular technique called GeneXpert MTB/RIF for rapid and accurate detection of MTB in pulmonary and extra pulmonary (EPTB) sites. GeneXpert (GX) is a quick, fully automated system that can be easily used with minimal training. The objective of this study was to evaluate the accuracy of the GX test for diagnosing MTB in pulmonary and extra pulmonary sites in Kurdistan /Iraq that is considered as endemic area for TB, as well as testing the ability of this technique to identify resistant strains of these bacilli to first line anti TB treatment. Methods: A total of 925 (504 male and 421 female) patients attended the TB center in Erbil/Iraq from Aug 2015 to Aug 2017. These patients were clinically diagnosed or suspected to have TB. Two sputum samples were collected from each patient and subjected to AFB smear staining. The other portion of the sputum was examined by GX assay and a number of cases were grown on L-J media. For extra pulmonary fluid samples, the same tests were done. Results: 743 were pulmonary samples and the remaining 182 case were extra pulmonary specimens (CSF, peritoneal aspirate, pleural fluid, urine and blood). Of these, 575 had their AFB smears done which was positive for in 184 (32%) and negative in 391 (68%) cases. On the other hand, real–time PCR using GeneXpert (GX) technology was positive in 228 (39.65%) while negative in 347 (60.34%) cases. The sensitivity and specificity of the GeneX VS AFB smear considering culture as a gold standard was 94.9% and 80.1% respectively. In addition, GX technique revealed that about 20 (14.3%) of positive MTB cases were resistant to Rifampicin therapy. Conclusion: The current study displayed the real significance of using GX test in diagnosing MTB in pulmonary and extrapulmonary specimens to save time and to avoid unnecessary anti TB treatment.