Performance of REBA MTB-XDR to detect extensively drug-resistant tuberculosis in an intermediate-burden country

Xpert MTB/XDR for detection of pulmonary tuberculosis and resistance to isoniazid, fluoroquinolones, ethionamide, and amikacin

BACKGROUND

The World Health Organization (WHO) End TB Strategy stresses universal access to drug susceptibility testing (DST). DST determines whether Mycobacterium tuberculosis bacteria are susceptible or resistant to drugs. Xpert MTB/XDR is a rapid nucleic acid amplification test for detection of tuberculosis and drug resistance in one test suitable for use in peripheral and intermediate level laboratories. In specimens where tuberculosis is detected by Xpert MTB/XDR, Xpert MTB/XDR can also detect resistance to isoniazid, fluoroquinolones, ethionamide, and amikacin.

OBJECTIVES

To assess the diagnostic accuracy of Xpert MTB/XDR for pulmonary tuberculosis in people with presumptive pulmonary tuberculosis (having signs and symptoms suggestive of tuberculosis, including cough, fever, weight loss, night sweats). To assess the diagnostic accuracy of Xpert MTB/XDR for resistance to isoniazid, fluoroquinolones, ethionamide, and amikacin in people with tuberculosis detected by Xpert MTB/XDR, irrespective of rifampicin resistance (whether or not rifampicin resistance status was known) and with known rifampicin resistance.

SEARCH METHODS

We searched multiple databases to 23 September 2021. We limited searches to 2015 onwards as Xpert MTB/XDR was launched in 2020.

SELECTION CRITERIA

Diagnostic accuracy studies using sputum in adults with presumptive or confirmed pulmonary tuberculosis. Reference standards were culture (pulmonary tuberculosis detection); phenotypic DST (pDST), genotypic DST (gDST),composite (pDST and gDST) (drug resistance detection).

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed reports for eligibility and extracted data using a standardized form. For multicentre studies, we anticipated variability in the type and frequency of mutations associated with resistance to a given drug at the different centres and considered each centre as an independent study cohort for quality assessment and analysis. We assessed methodological quality with QUADAS-2, judging risk of bias separately for each target condition and reference standard. For pulmonary tuberculosis detection, owing to heterogeneity in participant characteristics and observed specificity estimates, we reported a range of sensitivity and specificity estimates and did not perform a meta-analysis. For drug resistance detection, we performed meta-analyses by reference standard using bivariate random-effects models. Using GRADE, we assessed certainty of evidence of Xpert MTB/XDR accuracy for detection of resistance to isoniazid and fluoroquinolones in people irrespective of rifampicin resistance and to ethionamide and amikacin in people with known rifampicin resistance, reflecting real-world situations. We used pDST, except for ethionamide resistance where we considered gDST a better reference standard.

MAIN RESULTS

We included two multicentre studies from high multidrug-resistant/rifampicin-resistant tuberculosis burden countries, reporting on six independent study cohorts, involving 1228 participants for pulmonary tuberculosis detection and 1141 participants for drug resistance detection. The proportion of participants with rifampicin resistance in the two studies was 47.9% and 80.9%. For tuberculosis detection, we judged high risk of bias for patient selection owing to selective recruitment. For ethionamide resistance detection, we judged high risk of bias for the reference standard, both pDST and gDST, though we considered gDST a better reference standard. Pulmonary tuberculosis detection - Xpert MTB/XDR sensitivity range, 98.3% (96.1 to 99.5) to 98.9% (96.2 to 99.9) and specificity range, 22.5% (14.3 to 32.6) to 100.0% (86.3 to 100.0); median prevalence of pulmonary tuberculosis 91.3%, (interquartile range, 89.3% to 91.8%), (2 studies; 1 study reported on 2 cohorts, 1228 participants; very low-certainty evidence, sensitivity and specificity). Drug resistance detection People irrespective of rifampicin resistance - Isoniazid resistance: Xpert MTB/XDR summary sensitivity and specificity (95% confidence interval (CI)) were 94.2% (87.5 to 97.4) and 98.5% (92.6 to 99.7) against pDST, (6 cohorts, 1083 participants, moderate-certainty evidence, sensitivity and specificity). - Fluoroquinolone resistance: Xpert MTB/XDR summary sensitivity and specificity were 93.2% (88.1 to 96.2) and 98.0% (90.8 to 99.6) against pDST, (6 cohorts, 1021 participants; high-certainty evidence, sensitivity; moderate-certainty evidence, specificity). People with known rifampicin resistance - Ethionamide resistance: Xpert MTB/XDR summary sensitivity and specificity were 98.0% (74.2 to 99.9) and 99.7% (83.5 to 100.0) against gDST, (4 cohorts, 434 participants; very low-certainty evidence, sensitivity and specificity). - Amikacin resistance: Xpert MTB/XDR summary sensitivity and specificity were 86.1% (75.0 to 92.7) and 98.9% (93.0 to 99.8) against pDST, (4 cohorts, 490 participants; low-certainty evidence, sensitivity; high-certainty evidence, specificity). Of 1000 people with pulmonary tuberculosis, detected as tuberculosis by Xpert MTB/XDR: - where 50 have isoniazid resistance, 61 would have an Xpert MTB/XDR result indicating isoniazid resistance: of these, 14/61 (23%) would not have isoniazid resistance (FP); 939 (of 1000 people) would have a result indicating the absence of isoniazid resistance: of these, 3/939 (0%) would have isoniazid resistance (FN). - where 50 have fluoroquinolone resistance, 66 would have an Xpert MTB/XDR result indicating fluoroquinolone resistance: of these, 19/66 (29%) would not have fluoroquinolone resistance (FP); 934 would have a result indicating the absence of fluoroquinolone resistance: of these, 3/934 (0%) would have fluoroquinolone resistance (FN). - where 300 have ethionamide resistance, 296 would have an Xpert MTB/XDR result indicating ethionamide resistance: of these, 2/296 (1%) would not have ethionamide resistance (FP); 704 would have a result indicating the absence of ethionamide resistance: of these, 6/704 (1%) would have ethionamide resistance (FN). - where 135 have amikacin resistance, 126 would have an Xpert MTB/XDR result indicating amikacin resistance: of these, 10/126 (8%) would not have amikacin resistance (FP); 874 would have a result indicating the absence of amikacin resistance: of these, 19/874 (2%) would have amikacin resistance (FN).

AUTHORS' CONCLUSIONS

Review findings suggest that, in people determined by Xpert MTB/XDR to be tuberculosis-positive, Xpert MTB/XDR provides accurate results for detection of isoniazid and fluoroquinolone resistance and can assist with selection of an optimised treatment regimen. Given that Xpert MTB/XDR targets a limited number of resistance variants in specific genes, the test may perform differently in different settings. Findings in this review should be interpreted with caution. Sensitivity for detection of ethionamide resistance was based only on Xpert MTB/XDR detection of mutations in the inhA promoter region, a known limitation. High risk of bias limits our confidence in Xpert MTB/XDR accuracy for pulmonary tuberculosis. Xpert MTB/XDR's impact will depend on its ability to detect tuberculosis (required for DST), prevalence of resistance to a given drug, health care infrastructure, and access to other tests.

Diagnosis of Tuberculosis: Nanodiagnostics Approaches

Tuberculosis (TB) remains one of the most devastating infectious diseases worldwide. The burden of TB is alarmingly high in developing countries, where diagnosis latent TB infection (LTBI), Extra-pulmonary tuberculosis (EPTB), drug-resistant tuberculosis (DR-TB), HIV-associated TB, and paediatric TB is still a challenge. This is mainly due to delayed or misdiagnosis of TB, which continues to fuel its worldwide epidemic. The ideal diagnostic test is still unavailable, and conventional methods remain a necessity for TB diagnosis, though with poor diagnostic ability. The nanoparticles have shown potential for the improvement of drug delivery, reducing treatment frequency and diagnosis of various diseases. The engineering of antigens/antibody nanocarriers represents an exciting front in the field of diagnostics, potentially flagging the way toward development of better diagnostics for TB. This chapter discusses the presently available tests for TB diagnostics and also highlights the recent advancement in the nanotechnology-based detection tests for M. tuberculosis.

Performance of the GenoType MTBDRsl assay for the detection second-line anti-tuberculosis drug resistance

The rapid detection of drug-resistant tuberculosis (TB) is important to improve treatment outcomes and prevent disease transmission. The GenoType MTBDRsl assay (MTBDRsl assay) was developed to detect fluoroquinolone (FQ) and second-line injectable drug (SLID) resistance. The aim of this study was to evaluate the performance and clinical utility of MTBDRsl assay. We retrospectively reviewed patient medical records with MTBDRsl assay data between December 2011 and February 2017. MTBDRsl assay results were compared with that of phenotypic drug susceptibility testing. In addition, treatment outcomes were analyzed to evaluate the clinical utility of the MTBDRsl assay. Among 107 clinical isolates (84 cultured isolates and 23 sputum specimens), 85 (79.4%) were multidrug-resistant TB and 9 (8.4%) were extensively drug-resistant TB (XDR-TB). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of MTBDRsl assay for detecting FQ resistance was 87.5%, 94.7%, 87.5%, 94.7%, and 92.5%, respectively. The sensitivity, specificity, PPV, NPV, and accuracy of MTBDRsl assay for detecting SLID resistance was 88.9%, 98.9%, 94.1%, 97.8%, and 97.2%, respectively. Novel drugs such as bedaquiline and linezolid were more commonly used in patients with FQ or SLID resistance detected by the MTBDRsl assay and, probably therefore, the treatment outcome was favorable irrespective of FQ or SLID resistance. The MTBDRsl assay could be used as a rule-in test to detect FQ and SLID resistance. By detecting FQ- and SLID-drug resistance rapidly, novel or repurposed drugs could be initiated earlier, suggesting that better treatment outcomes would be expected in patients with pre-XDR- and XDR-TB.

Treatment Outcomes of Patients Treated for Pulmonary Tuberculosis after Undergoing Gastrectomy

Gastrectomy is a proxy of malnutrition, which may lead to increased risk for developing pulmonary tuberculosis (TB). Malabsorption in gastrectomy patients could lead to low serum levels of rifampicin, which may be related to higher treatment failure. However, there is limited information on treatment outcomes of TB in patients who have undergone gastrectomy. This study aims to determine treatment outcomes and adverse effects in patients treated for TB after undergoing gastrectomy for gastric cancer. During the study period, 112 patients were treated for active TB that developed after gastrectomy for gastric cancer. Among them, we selected 15 patients who were culture positive at initial diagnosis and had evidence of active TB on imaging studies; namely, the remaining 97 patients without initial culture or imaging studies were excluded. We thus performed a case-control study of gastric cancer patients treated for TB after undergoing gastrectomy (n = 15). The control group was defined as age- and sex-matched TB patients who had not received gastrectomy (n = 45). Treatment failure in clinical, microbiological aspects, and adverse events were analyzed. Patients who had undergone gastrectomy exhibited higher 4-month clinical failure rates, compared to non-gastrectomy patient: 4 (26.7%) vs. 1 (2.2%), P = 0.012. Gastrointestinal adverse effects were more frequent in patients with gastrectomy, compared to non-gastrectomy patients: 9 (60%) vs. 5 (11.1%), P < 0.001. In conclusion, patients treated for TB after undergoing gastrectomy are associated with higher rates of gastrointestinal adverse events and treatment failure.

Some Synonymous and Nonsynonymous gyrA Mutations in Mycobacterium tuberculosis Lead to Systematic False-Positive Fluoroquinolone Resistance Results with the Hain GenoType MTBDRsl Assays

In this study, using the Hain GenoType MTBDRsl assays (versions 1 and 2), we found that some nonsynonymous and synonymous mutations in gyrA in Mycobacterium tuberculosis result in systematic false-resistance results to fluoroquinolones by preventing the binding of wild-type probes. Moreover, such mutations can prevent the binding of mutant probes designed for the identification of specific resistance mutations. Although these mutations are likely rare globally, they occur in approximately 7% of multidrug-resistant tuberculosis strains in some settings.

Wild-Type and Non-Wild-Type Mycobacterium tuberculosis MIC Distributions for the Novel Fluoroquinolone Antofloxacin Compared with Those for Ofloxacin, Levofloxacin, and Moxifloxacin

Antofloxacin (AFX) is a novel fluoroquinolone that has been approved in China for the treatment of infections caused by a variety of bacterial species. We investigated whether it could be repurposed for the treatment of tuberculosis by studying its in vitro activity. We determined the wild-type and non-wild-type MIC ranges for AFX as well as ofloxacin (OFX), levofloxacin (LFX), and moxifloxacin (MFX), using the microplate alamarBlue assay, of 126 clinical Mycobacterium tuberculosis strains from Beijing, China, of which 48 were OFX resistant on the basis of drug susceptibility testing on Löwenstein-Jensen medium. The MIC distributions were correlated with mutations in the quinolone resistance-determining regions of gyrA (Rv0006) and gyrB (Rv0005). Pharmacokinetic/pharmacodynamic (PK/PD) data for AFX were retrieved from the literature. AFX showed lower MIC levels than OFX but higher MIC levels than LFX and MFX on the basis of the tentative epidemiological cutoff values (ECOFFs) determined in this study. All strains with non-wild-type MICs for AFX harbored known resistance mutations that also resulted in non-wild-type MICs for LFX and MFX. Moreover, our data suggested that the current critical concentration of OFX for Löwenstein-Jensen medium that was recently revised by the World Health Organization might be too high, resulting in the misclassification of phenotypically non-wild-type strains with known resistance mutations as wild type. On the basis of our exploratory PK/PD calculations, the current dose of AFX is unlikely to be optimal for the treatment of tuberculosis, but higher doses could be effective.