GeneXpert MTB RIF assay : a major milestone for diagnosing mycobacterium tuberculosis and rifampicin-resistant cases in pulmonary and extrapulmonary specimens

Abstract EN

Background and Objective: Tuberculosis (TB) is an endemic disease in Iraq.

Many methods are available to diagnose pulmonary and extrapulmonary TB (EPTB).

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 the presence of TB.

The WHO has recommended the use of a gene‑based molecular technique called GeneXpert (GX) MTB/rifampicin (RIF) for rapid and accurate detection of MTB in pulmonary and extrapulmonary (EPTB) sites.

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 extrapulmonary sites in Kurdistan/Iraq that is considered as an endemic area for TB, as well as testing the ability of this technique to identify the resistant strains of these bacilli to first‑line anti‑TB treatment.

Methodology: A total of 925 (504 males and 421 females) patients attended the TB center in Erbil/Iraq from August 2015 to August 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 portions of the sputum were examined by GX assay, and a number of cases were grown on the Lowenstein–Jensen media.

For extrapulmonary fluid samples, the same tests were done.

Results: Seven hundred and forty‑three were pulmonary samples, and the remaining 182 cases were extrapulmonary specimens (cerebrospinal fluid, 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 polymerase chain reaction using GX technology was positive in 228 (39.65%) while negative in 347 (60.34%) cases.

The sensitivity and specificity of the GeneX versus AFB smear considering culture as a gold standard were 94.9% and 80.1%, respectively.

In addition, GX technique revealed that about 20 (14.3%) of positive MTB cases were resistant to RIF 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.