Rapid Molecular Detection of Extrapulmonary Tuberculosis by the Automated GeneXpert MTB/RIF System

Abstract

Twenty (3.8%) of the 521 specimens gave no interpretable result. Whereas the sensitivity of the Xpert assay with tissue specimens was 69.0% (20 out of 29 culture-positive cases detected), 100% sensitivity was found with the urine and stool specimens. The combined sensitivity and specificity of the Xpert assay were calculated to be 77.3% and 98.2%, respectively.With an estimated 9 million new cases and 2 million deaths every year, tuberculosis (TB) remains a leading public health problem worldwide (6). In the majority of cases, the disease affects the lungs, but there are also not negligible numbers of cases (about 15%) with extrapulmonary involvement in lowincidence countries. There are even higher rates in high-incidence countries. HIV-coinfected TB patients often develop extrapulmonary involvement and may progress rapidly unless the infection is diagnosed and they are treated appropriately (8).Extrapulmonary infection with members of the Mycobacterium tuberculosis complex (MTBC) remains a diagnosis that is often difficult to establish, since the number of bacteria in extrapulmonary specimens is often lower than the number in pulmonary specimens. Furthermore, collection of extrapulmonary material often requires invasive procedures, and it is not easy to obtain additional samples. In recent times, attention has been devoted to new nucleic acid amplification diagnostic technologies, owing to their rapidity, sensitivity, and specificity.One of the latest systems, the GeneXpert MTB/RIF (Xpert) assay, was evaluated only recently in a large study with pulmonary specimens. The Xpert assay uses heminested real-time PCR to amplify an M. tuberculosis-specific sequence of the rpoB gene. To determine rifampin (RMP) resistance, the rifampin resistance-determining region of the rpoB gene is probed with molecular beacons (7). The assay can be carried out in a nearly fully automated manner, including bacterial lysis, nucleic acid extraction and amplification, and amplicon detection. The test runs on the GeneXpert platform (Cepheid, Sunnyvale, CA) using a disposable plastic cartridge with all required reagents (16).It could be shown that the Xpert assay detected pulmonary TB in all TB patients, including over 90% of smear-negative patients, with a high sensitivity of over 97% (2). The purpose of this study was to test the efficiency and reliability of the Xpert system for the detection of M. tuberculosis bacteria in extrapulmonary specimens and to compare it to conventional culture methods. MATERIALS AND METHODSSpecimens. All nonrespiratory specimens that were submitted to the German National Reference Laboratory for Mycobacteria (NRL) from May 2009 to August 2010 were included in the study. The specimens originated from patients with suspected M. tuberculosis or nontuberculous mycobacterial (NTM) infection on the basis of clinical criteria or to rule out these infections. Consecutive specimens were used, and specimens were not selected by the use of special criteria. In total, 521 specimens were tested. These comprised 91 urin...

Evaluation of rapid GeneXpert MTB/RIF method using DNA tissue specimens of vertebral bones in patients with suspected spondylitis TB

“…8,20 Currently, various PCR studies have developed into GeneXpert MTB/RIF method using heminested real-time polymerase chain reaction (PCR) assay. 11,17,21 This system works automatically toward the lysis of bacteria, extraction of the DNA, amplifications, and the detection of amplicon in a single system using a rapid approach. 11 Sensitivity and specificity of GeneXpert MTB/RIF have been compared with the gold standard method on MGIT medium in which it shown values of 100% and 16.6%, respectively.…”

“…11 After centrifugation, the pellet will be suspended into 1-1.5 ml of sterile buffer phosphate (pH 6.8). Then, samples will be centrifuged at a speed of 3000 Â g for 15 min.…”

“…It also had 97% sensitivity rate. 11,14 The Medical Research Council Committee for Research of Tuberculosis in the Tropics described that isoniazid and rifampicin must be regularly given during the period of treatment. This statement is parallel with a study conducted by Karaeminogullari et al 15 that cures spondylitis TB patient with rifampicin and isoniazid for nine months with satisfying results.…”

“…GeneXpert MTB/RIF is one of the current systems that is widely explored to detect tuberculosis. 11 GeneXpert MTB/RIF using heminested real-time polymerase chain reaction (PCR) assay to multiply specific DNA sequences of M. tuberculosis from the rifampicin-resistant rpoB gene. Rifampicin resistance (RMP) from GeneXpert is discovered by determining the area of the rpoB gene that will be examined using molecular beacon as the probe.…”

GeneXpert: a game changer in the detection and diagnosis of childhood tuberculosis

“…[13][14][15][16][17][18][19] The focus of these studies were on pulmonary tuberculosis while there is limited data on the diagnostic utility of extrapulmonary tuberculosis. [20][21][22][23][24][25][26][27] Studies of diagnostic utility of geneXpert study in the pediatric population is limited, more so from Indian population. Available data is on adult Indian population.…”