Microbiological diagnosis of tuberculous meningitis: Phenotype to genotype

Tuberculous meningitis (TBM) is a commonly encountered central nervous system infection. Characteristic clinical, imaging and cerebrospinal fluid parameters help clinicians to make a prompt presumptive diagnosis that enables them to start empirical anti-tuberculosis treatment. There are several close mimic to TBM, such as partially treated pyogenic meningitis, fungal meningitis, sarcoidosis, meningeal metastases and meningeal lymphomatosis. Microbiological confirmation instils a sense of confidence amongst treating physicians. With conventional phenotypic methods (cerebrospinal fluid microscopy and culture), in more than 50 per cent patients, microbiological confirmation is not achieved. Moreover, these methods take a long time before providing conclusive results. Negative result does not rule out Mycobacterium tuberculosis infection of the brain. Genotypic methods, such as IS 6110 polymerase chain reaction and automated Xpert M. tuberculosis/rifampicin (MTB/RIF) assay system improved the TBM diagnostics, as results are rapidly available. Xpert MTB/RIF assay, in addition, detects rifampicin resistance. Xpert MTB/RIF Ultra is advanced technology which has higher (60-70%) sensitivity and is being considered a game-changer in the diagnostics of TBM. A large number of TBM cases remain unconfirmed. The situation of TBM diagnostics will remain grim, if low-cost technologies are not widely available. Till then, physicians continue to rely on their clinical acumen to start empirical anti-tuberculosis treatment.

Diagnostic accuracy of Xpert MTB/RIF assay in extrapulmonary tuberculosis

Introduction: The WHO endorsed Xpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) assay, has been evaluated for pulmonary TB in a number of studies but very few have investigated it for extrapulmonary specimens. The present study evaluates the performance of Xpert MTB/RIF assay in the diagnosis of extrapulmonary TB (EPTB). Aim and Objectives: The aim of the study is to determine sensitivity and specificity of Xpert MTB/RIF assay for diagnosis of EPTB and RIF resistance in comparison to culture on Lowenstein–Jensen (LJ) medium and proportion method (PM), respectively. Materials and Methods: A total of 738 specimens from clinically suspected cases of EPTB were subjected to Ziehl–Neelsen staining, Xpert MTB/RIF assay and culture on LJ medium. PM was done on MTB isolates. Results: The sensitivity, specificity of Xpert MTB/RIF assay for diagnosis of EPTB were 84.91% (95% confidence interval [CI] 72.41%–93.25%) and 86.72% (95% CI 83.94%–89.17%) and for RIF resistance detection were 60.00% (95% CI 32.29%–83.66%) and 94.74% (95% CI 73.97%–99.87%), respectively. Among culture-positive cases, the sensitivity of Xpert MTB/RIF assay was 94.12% in smear positive and 80.56% in smear-negative cases. Xpert MTB/RIF showed maximum sensitivity of MTB detection from lymph node specimens (100% [95% CI 54.07%–100.00%]) and other body fluids (100% [95% CI 15.81%–100.00%]). Conclusion: The present study establishes Xpert MTB/RIF assay as a promising tool in the rapid diagnosis of EPTB and detection of RIF resistance.

An evaluation of false-positive rifampicin resistance on the Xpert MTB/RIF

BACKGROUND Mycobacterium tuberculosis (MTB) is one of the most significant causes of mortality and morbidity. Early diagnose is important especially in multiple drug resistant tuberculosis to avoid transmission. Traditional techniques requires at least one to three weeks for diagnosis of tuberculosis. Diagnostic delays with multiple drug resistant tuberculosis are associated with worse clinical outcomes and increased transmission The Xpert MTB/RIF assay is one of the new diagnostic device for the diagnosis of tuberculosis and rapid detection of rifampicin resistance. OBJECTIVE We assessed the performance of Xpert MTB/RIF assay for detecting rifampicin resistance using phenotypic drug susceptibility tests as automated BD MGIT 960. METHODS Total of 2136 specimens were included in the study. Xpert MTB/RIF testing was performed on samples, using version 4 cartridges, according to the manufacturer's recommendations. The MTBC culture and first-line phenotypic DST were performed in automated BD MGIT 960 (Becton & Dickinson, USA) according to the recommendations of the manufacturer. Agar proportion was used in the case of inconsistency for rifampicin resistance. FINDINGS Thirty-four samples (19 respiratory and 15 nonrespiratory samples) were determined as positive for M. tuberculosis complex by Xpert MTB/RIF (Cepheid GeneXpert® System, USA). Xpert MTB/RIF assay detected 4/34 (11.7%) specimens as rifampicin resistant. One of the rifampicin resistant isolates was determined susceptible in MGIT 960 automated system. This isolate was also tested with agar proportion method and found susceptible to rifampicin. MAIN CONCLUSION The Xpert MTB/RIF assay can be used as first-line assay for the detection of M. tuberculosis. However, microbiologists must be aware of the limitations of the assay.

Evaluation of Xpert MTB/RIF assay performance in the diagnosis of abdominal tuberculosis

BACKGROUND/AIMS: The use of genetic probes for the diagnosis of pulmonary tuberculosis (TB) has been well described. However, the role of these assays in the diagnosis of intestinal tuberculosis is unclear. We therefore assessed the diagnostic utility of the Xpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) assay, and estimated the prevalence of multidrug-resistant (MDR) TB in the Indian population. METHODS: Of 99 patients recruited, 37 had intestinal TB; two control groups comprised 43 with Crohn's disease (CD) and 19 with irritable bowel syndrome. Colonoscopy was performed before starting any therapy; mucosal biopsies were subjected to histopathology, acid-fast bacilli staining, Lowenstein-Jensen culture, and nucleic acid amplification testing using the Xpert MTB/RIF assay. Patients were followed up for 6 months to confirm the diagnosis and response to therapy. A composite reference standard was used for diagnosis of TB and assessment of the diagnostic utility of the Xpert MTB/RIF assay. RESULTS: Of 37 intestinal TB patients, the Xpert MTB/RIF assay was positive in three of 37 (8.1%), but none had MDR-TB. The sensitivity, specificity, positive predictive value, and negative predictive value of the Xpert MTB/RIF assay was 8.1%, 100%, 100%, and, 64.2%, respectively. CONCLUSIONS: The Xpert MTB/RIF assay has low sensitivity but high specificity for intestinal TB, and may be helpful in endemic tuberculosis areas, when clinicians are faced with difficulty differentiating TB and CD. Based on the Xpert MTB/RIF assay, the prevalence of intestinal MDR-TB is low in the Indian population.

Diagnostic value of four techniques of detecting the Mycobacterium tuberculosis in bronchoalveolar la-vage fluid in tracheobronchial tuberculosis / 实用医学杂志

Objective To assess the value of four different techniques of detecting the Mycobacterium tuberculosis (MTB) in bronchoalveolar lavage fluid (BALF) in the diagnosis of tracheobronchial tuberculosis. Methods A total of 98 patients diagnosed as tracheobronchial tuberculosis were selected from May 1,2013 to June 30,2016. The clinical data was analyzed retrospectively,and the positive rates of MTB of the 960 cultrue, the direct smears , the modified Ziehl?Neelsen stain method and Xpert MTB/RIF assay were compared. Results The positive rates of the 960 cultrue,the direct smears,the modified Ziehl?Neelsen stain method and Xpert MTB/RIF assay were 20.4%(20/98),15.3%(15/98),70.4%(69/98) and 74.5%(73/98),respectively. Among the four techniques ,the positive rates of the modified Ziehl?Neelsen stain method and Xpert MTB/RIF assay were significantly higher than those of the 960 cultrue and the direct smears(P 0.05). Conclusions The modified Ziehl?Neelsen stain method and Xpert MTB/RIF assay for detecting the MTB in BALF have high clinical value in the diagnosis of tracheobronchial tuberculosis.

Diagnostic Efficacy Of Gene X-Pert/ MTB-RIF Assay And Its Implication For The Treatment Of MDR TB In Rural Medical College.

Aims and objectives: To diagnose and treat the MDR Tuberculosis by XPERT MTB/RIF assay as early as possible so that transmission of infection can be minimized and To find out prevalence of MDR TB in our rural district of Maharashtra. Methods: This is a observational ,prospective study conducted over a period of 14 months ( Jan 15 to April 16 ) in the Dept. of Pulmonary Medicine, Shri Vasantrao Naik Gov.t Medical College, Yavatmal, Maharashtra. We have subjected 613 patients who fulfill the clinical criteria for RNTCP - MDRTB suspect 1.Treatment failure. 2. Retreatment case sputum positive at the end of 4 months, 3.Contact of known MDRTB case, 4.Sputum positive at diagnosis, retreatment case, 5. Any follow up sputum positive, 6.Other category (sputum negative retreatment cases), and 7. HIV-TB Cases. We have excluded all new cases (sputum positive, sputum negative and extrapulmonary cases ). With all precautions two sputum samples collected in the designated microscopy centre. One sample was subjected for routine ZN staining and other one for GENE X-PERT MTB/RIF assay. Result. Out of 613 MDR suspect subjects, 314 (51.23%) were found in the age group 30 to 50 which is economically productive age group. There were 428 (69.82%) male and 185 (30.18%) female. Out of total study patient 44 (7.18 %) were detected Rifampicin resistance by X-PERT MTB/RIF assay. Amongst MDR suspect criteria highest no (4.07 %) of Rifampicin resistant were found in Retreatment cases ( group 4 ) followed by 1.47 % in any follow up sputum positive ( group 5 ) , 0.65 % in sputum negative retreatment cases ( group 6), 0.32 % in treatment failure ( group 1 ) , 0.49 % in HIV TB cases (group7 and0.16 % in contacts of known MDR ( group 3) .There were 144 ( 23 .5 ) were co infected with HIV.TB. Conclusion: We conclude that GENE XPERT MTB /RIF assay has significant role in detecting Rifampicin resistance, patient can be started on treatment at the earliest thereby reducing morbidity, progression to XDR, mortality and transmission of MDR/XDR TB in the community can be minimized. However it has some shortcomings that it cannot detect resistance of other anti- tubercular drugs and atypical mycobacteria.[B.B.Bhadke NJIRM 2016; 7(5):33-39]