Xpert MTB/RIF test for rapid diagnosis of Mycobacterium tuberculosis and simultaneous detection of multidrugresistant tuberculous bacillus / 解放军医学杂志

ABSTRACT

Tuberculosis (TB) is endemic in China with high prevalence of multiple-drug resistant tuberculous bacilli (MDRTB). The incidence of new cases of TB reaches 1,300 thousand annually. Among them, 5.7 percent are MDR-TB. Staining for acidfast bacilli in sputum and clinicoradiological examination have been the main diagnostic tools for TB, particularly pulmonary TB. However, the positive rate of sputum Ziehl-Neelsen stain for sputum is disappointedly low, merely 28% in newly-diagnosed TB. Moreover, the radiological manifestations of the patients suspected of TB are often non-specific. All these facts call for a simple, accurate and rapid diagnostic method to overcome this bottleneck, which hinders the success of satisfactory TB control in China. Employing both hemi-nested RT-PCR and beacon technology with fluorescent probes, the MTB/RIF diagnostic assay specifically amplifies, thus helps detect the rpoB gene, which is unique to Mycobacterium tuberculosis and also a biomolecularmarker of rifampin resistance. As a semi-quantitative analysis, the quantity of Mycobacterium tuberculosis in samples is reflected by the threshold of PCR cycles during MTB/RIF assay. With Mycobacterium tuberculosis culture as the standard reference, for sputum samples from patients suspected of suffering from pulmonary TB, overall diagnostic sensitivity of MTB/RIF assay is 73.1%-90.0% with a specificity of 99.0%-99.5%. For detection of rpoB gene mutations responsible for rifampin-resistance, the sensitivity is 97.2% and specificity is 98.3%. Following sample loading, the system can automatically complete the diagnostic process and report the results within 2 hours. Targeting the rpoB gene specifically, there is no cross-reaction with non-tuberculosis mycobacteria or other common respiratory pathogens. In addition to sputum samples, the system can be used to detect Mycobacterium tuberculosis in various body fluids (including pleural effusion, urine, cerebrospinal fluid and even bronchoalveolar lavage fluid) and lung tissue biopsy samples. As for sensitivity, the assay is comparable to Mycobacterium tuberculosis culture (for the latter, mean interval between loading and result-reporting is 16 or 30 days (depending upon the culture medium used), and it is 100 times longer than Ziehl-Neelsen stains. Compared with conventional laboratory diagnostic approaches, this assay is much simpler and biohazardous aerosol-free.