Rifampicin-resistant Mycobacterium tuberculosis: susceptibility to isoniazid and other anti-tuberculosis drugs

Updates in pulmonary drug-resistant tuberculosis pharmacotherapy: A focus on BPaL and BPaLM

Drug-resistant tuberculosis (TB) is a major public health concern and contributes to high morbidity and mortality. New evidence supports the use of shorter duration, all-oral regimens, which represent an encouraging treatment strategy for drug-resistant TB. As a result, the landscape of drug-resistant TB pharmacotherapy has drastically evolved regarding treatment principles and preferred agents. This narrative review focuses on the key updates of drug-resistant TB treatment, including the use of short-duration all-oral regimens, while calling attention to current gaps in knowledge that may be addressed in future observational studies.

Performance of WHO-Endorsed Rapid Tests for Detection of Susceptibility to First-Line Drugs in Patients with Pulmonary Tuberculosis in Bangladesh

The fast and accurate detection of susceptibility in drugs is a major challenge for a successful tuberculosis (TB) control programme. This study evaluated the performance of WHO-endorsed rapid diagnostic tools, such as BACTEC MGIT 960 SIRE (MGIT SIRE), GenoType MTBDRplus (MTBDRplus) and Xpert MTB/RIF (Xpert), for detecting susceptibility to first-line anti-TB drugs among pulmonary TB patients in Bangladesh. A total of 825 sputum samples with results from drug susceptibility testing (DST) against first-line anti-TB drugs in the MGIT SIRE, MTBDRplus and Xpert assays were evaluated and compared with the gold standard proportion susceptibility method of the Lowenstein–Jensen (LJ) medium. The overall sensitivities of MGIT SIRE were 97.6%, 90.0%, 61.3% and 44.9%, while specificities were 89.9%, 94.5%, 91.3% and 92.2% for detection of susceptibility to isoniazid (INH), rifampicin (RIF), streptomycin (STR) and ethambutol (EMB), respectively. For MTBDRplus, the sensitivities were 88.0% and 88.7%, and the specificities were 97.4% and 97.8% for the detection of susceptibility to INH and RIF, respectively. Xpert demonstrated a sensitivity and specificity of 94.8% and 99.5%, respectively, for the detection of RIF susceptibility. All tests performed significantly better in retreated TB patients compared with primary TB cases. For detection of RIF and INH susceptibility, all three assays showed almost perfect agreement with the LJ method, although MGIT SIRE exhibited low agreement for STR and EMB. Considering the high performance, shorter turnaround time and ease of use, molecular-based approaches Xpert and MTBDRplus can be widely implemented throughout the country for the rapid detection of drug-resistant TB.

Design and synthesis of leucylaniline derivatives as leucyl-tRNA synthetase inhibitors

By simulating the structure of Leu-AMP, 26 leu-arylamine derivatives were designed and synthesized as leucyl-tRNA Synthetase inhibitors; compounds 19 and 24 showed good anti-tuberculosis activity.

Risk factors for mortality and multidrug resistance in pulmonary tuberculosis in Guatemala: A retrospective analysis of mandatory reporting

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National TB cohort analyzing risk factors associated with MDR-TB and mortality in Guatemala.

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Indigenous ethnicity and prior TB treatment were associated with increased risk of mortality and MDR-TB.

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HIV/Unknown HIV status were associated with increased mortality and diabetes with risk for MDR-TB.

Background

Risk factors for mortality and MDR-TB in Guatemala are poorly understood. We aimed to identify risk factors to assist in targeting public health interventions.

Methods

We performed a retrospective study of adults with pulmonary TB reported to the Guatemalan TB Program between January 1, 2016 and December 31, 2017. The primary objective was to determine risk factors for mortality in pulmonary TB. The secondary objective was to determine risk factors associated with MDR-TB.

Results

Among 3,945 patients with pulmonary TB, median age was 39 years (IQR 25–54), 59% were male, 25% of indigenous ethnicity, 1.1% had MDR-TB and 3.9% died. On multivariable analysis, previous TB treatment (odds ratio [OR] 3.57, CI 2.24–5.68 [p < 0.001]), living with HIV (OR 3.98, CI 2.4–6.17 [p < 0.001]), unknown HIV diagnosis (OR 2.65, CI 1.68–4.18 [p < 0.001]), indigenous ethnicity (OR 1.79, CI 1.18–2.7 [p = 0.005]), malnutrition (OR 7.33, CI 3.24–16.59 [p < 0.001]), and lower educational attainment (OR 2.86, CI 1.43–5.88 [p = 0.003]) were associated with mortality. Prior treatment (OR 53.76, CI 25.04–115.43 [p < 0.001]), diabetes (OR 4.13, CI 2.04–8.35 [p < 0.001]), and indigenous ethnicity (OR 11.83, CI 1.46–95.73 [p = 0.02]) were associated with MDR-TB.

Conclusions

In Guatemala, both previous TB treatment and indigenous ethnicity were associated with higher TB mortality and MDR-TB risk among patients with pulmonary TB.

Molecular diversity survey on diarrheagenic Escherichia coli isolates among children with gastroenteritis in Fars, Iran

Aim: To differentiate Escherichia coli isolates from diarrheal pediatric patients in clinical laboratories. Materials & methods: Patients with watery diarrhea were selected for sampling and tested for diarrheagenic E. coli (DEC) by API kit. DEC isolates were tested for phylotyping, pathotyping and presence of determined virulence-encoding genes by specific molecular methods. Results: About 50% of isolates were detected as DECs (>55 and >31% were categorized B2 and D phylotypes respectively). Enterotoxigenic E. coli was the most and enteroinvasive E. coli was the lowest prevalent pathotypes. csg and fim genes were the most present virulence factors. Conclusion: Typing of E. coli isolates from stool specimens will help to determine the diversity of diarrheal pathogens and take proper decisions to reduce the health burden of diarrheal diseases.

GeneXpert Mycobacterium tuberculosis/rifampicin assay for molecular epidemiology of rifampicin-Resistant Mycobacterium tuberculosis in an Urban Setting of Banten province, Indonesia

Background

Tuberculosis (TB) is the fourth leading cause of death in Indonesia. In 2017, the World Health Organization (WHO) estimated that only 2% of the TB patients in Indonesia had only been tested with rapid diagnostics at the time of diagnosis, resulting in largely underdetected rifampicin-resistant TB (RR-TB). Utilization of GeneXpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) assay as a point-of-care molecular assay to detect TB and RR-TB and serving its purpose in accordance with the first pillar of the WHO End-TB Strategy.

Objective

This study investigated the use of GeneXpert MTB/RIF assay to determine the molecular epidemiology of RR-TB in an urban setting of Indonesia.

Methods

All molecular epidemiological and microbiological databases were retrospectively examined from GeneXpert MTB/RIF assay results in Siloam Hospital Lippo Village. The sociodemographic characteristics and results of microbiological examinations consisting of Ziehl-Neelsen staining and GeneXpert MTB/RIF assay were analyzed.

Results

During the study period, 600 cases were registered, and GeneXpert MTB/RIF tests were done in which the tests yielded 597 (99.5%) valid results; 62.0% were male and adult of age category; of whom 29 samples (4.9%) were found to be RR-TB, 186 samples (31.2%) were RIF sensitive, and remainders were negative.

Conclusions

The results of GeneXpert MTB/RIF to be a fundamental diagnosis of RR-TB and subsequently to notify MDR-TB were satisfying and valuable in this study. This further increased and reinforced TB surveillance and national TB program to finally bring about WHO end-TB strategy one step closer in Indonesia.

Longitudinal Analysis of Prevalence and Risk Factors of Rifampicin-Resistant Tuberculosis in Zhejiang, China

Objectives

To investigate the factors associated with rifampicin-resistant tuberculosis among drug resistant tuberculosis patients and to determine the correlation of rifampicin-resistant TB with MDR-TB in a high MDR-TB burden province of china.

Methods

A retrospective longitudinal analysis on four surveys of anti-TB drug resistance done in 1998, 2003, 2008, and 2013 in Zhejiang province, China. 4289 sputum-smear microscopy positive suspected tuberculosis patients were eligible at 30 investigation points, chosen by stratified random sampling at survey sites from all over the province. Culturing samples in L-J medium and the drug-susceptibility testing for the 4 first-line anti-TB drugs were performed to all patients. Multivariate logistic regression was carried out to determine the factors associated with the rifampicin-resistance in the study population.

Results

Overall, there were 3832 patients with positive mycobacterial cultures, and 2813 of the isolates (73.4%) were susceptible to all 4 first-line drugs. Analysis of rifampin monoresistant (RMR) TB indicated the prevalence was 1.1% in new cases and 3.4% in previously treated cases. Among the 359 rifampicin resistant TB (RR-TB) cases, 279 (77.7%) were also resistant to isoniazid, indicating MDR-TB. From 1998 to 2013, the proportion of MDR-TB among rifampicin-resistant TB cases varied between 80.0% and 87.5% (P for trend: 0.768) among previously treated cases and varied from 68.6% to 79.5% (P for trend: 0.403) among new cases. Among previously treated patients, those who received treatment for less than 6 months were less likely to have drug resistant TB (OR: 0.40, 95% CI: 0.16–0.97) or MDR-TB (OR: 0.24, 95% CI: 0.07–0.81). Patients who received anti-TB treatment in a general hospital were less likely to develop MDR-TB than those treated in a TB clinic (OR: 0.08, 95% CI: 0.01–0.72).

Conclusion

This study highlights a high proportion of RMR-TB among new RR-TB cases in Zhejiang, China. The management of treatment with rapid and accurate diagnosis of MDR-TB other than only relying on RIF susceptibility testing is crucial for improving adherence and outcomes in patients with drug-resistant TB.

Multidrug-resistant Disseminated Tuberculosis Related to Infliximab in a Patient with Ulcerative Colitis and Negative Evaluation for Latent Tuberculosis

Anti-tumor necrosis factor (anti-TNF) is an effective biological agent for the treatment of moderate-to-severe active ulcerative colitis (UC) refractory to conventional therapy. On the other hand, anti-TNF therapy is strongly associated with a potential risk of tuberculosis (TB). Active TB is a critical complication that makes it difficult to treat patients who require anti-TNF for the treatment of UC refractory to conventional therapy. Based on the clinical guidelines, patients with inflammatory bowel disease (IBD) are strongly recommended to screen for latent TB before anti-TNF administration. Considering the possibility of active or reactivated TB related to anti-TNF therapy, all patients with IBD should be monitored closely for TB during anti-TNF therapy, irrespective of the screening results for latent TB. In particular, the risk of anti-TNF-related multidrug-resistant TB (MDR-TB) in patients with IBD has not been elucidated. This paper reports the first case of disseminated MDR-TB that developed in a UC patient receiving infliximab despite the negative evaluation for latent TB screening.

How Can the Tuberculosis Laboratory Aid in the Patient-Centered Diagnosis and Management of Tuberculosis?

In 2019, tuberculosis is still a global source of morbidity and mortality. To determine and provide the most effective treatment regimen to patients, the tuberculosis laboratory needs to rapidly but reliably answer 2 main questions: (1) Is Mycobacterium tuberculosis detectable in the patient specimen? and (2) If so, is the strain detected drug susceptible or does it show any form of drug resistance? In cases of drug resistance, health care providers need to have access to minimal inhibitory concentration results and to the type of mutation conferring drug resistance to tailor the most appropriate drug regimen.

Improving the diagnostics of tuberculosis and drug resistance with Xpert MTB/RIF in a district general hospital in Sierra Leone: a quality improvement project

Sierra Leone has a high tuberculosis (TB) burden with a prevalence of 441 cases per 100 000 population. As a result of the Global Fund, some facilities in the country have access to improved diagnostics, including Xpert MTB/RIF testing, of particular use in diagnosing those at risk of drug resistance, in the form of rifampicin-resistant (RR) TB. This quality improvement project describes how a small, rural district general hospital in Masanga village improved the diagnosis of TB and RR-TB by creating a formal link with the regional hospital in Makeni city. In an effort to improve diagnosis, all patients with a suspicion of TB and one of the following would have a sample sent for Xpert MTB/RIF testing: previous TB treatment (of any course length), HIV positive or known contact of a RR-TB case. The samples were transported by the logistics team, who already drove weekly from Masanga to Makeni for supplies, and the results were texted to the clinician in charge of the medical ward. Over the course of the first 4 months of this intervention, 34 samples had Xpert MTB/RIF testing performed compared with two samples in the previous 12 months since the machine had been installed. This yielded nine additional diagnoses of TB (in patients with negative or unavailable smear results) and five diagnoses of RR-TB with subsequent appropriate isolation and transfer to the central tertiary centre. This study shows that it is feasible to centralise Xpert MTB/RIF testing in low-resource settings using creative methods for sample transfer and results dissemination, leading to both improved diagnostics and infection control.

Low prevalence of MDR-TB in Lao PDR: results from the first national anti-tuberculosis drug resistance survey

OBJECTIVE

To present results of the first national anti-tuberculosis (TB) drug resistance survey conducted in Lao PDR between May 2016 and August 2017 to determine the prevalence of resistance to first-line anti-TB drugs among new and previously treated pulmonary TB cases in the country.

METHODS

Patients with sputum smear-positive pulmonary TB were enrolled from 42 TB laboratories distributed in 40 clusters throughout the country. Survey sites were selected using probability-proportional-to-size sampling among all diagnostic centres in the country. In addition to smear microscopy, all patients underwent Xpert MTB/RIF testing and those found positive to Mycobacterium tuberculosis underwent sputum culture and drug susceptibility testing using the proportion method on solid Löwenstein-Jensen medium.

RESULTS

Among 1006 eligible patients, 946 sputum smear-positive and Xpert MTB/RIF positive (Mycobacterium tuberculosis detected) patients were included in the survey, comprising 897 new and 49 previously treated TB cases. The prevalence of rifampicin-resistant TB was 1.2% (95% CI: 0.5-2.0%, n = 11/897) among new cases and 4.1% (95% CI: 0-9.6%, n = 2/49) among previously treated cases. Among the 946 TB cases confirmed by Xpert MTB/RIF, phenotypic drug sensitivity testing was available for 820 (776 new and 44 previously treated). The prevalence of multidrug-resistant TB (MDR-TB) was 0.5% (95% CI: 0-1.0%, n = 4/776) among new cases and 2.3% (95% CI: 0-6.7%, n = 1/44) among previously treated cases. No resistance to second-line injectable agents nor to fluoroquinolones was detected among MDR-TB patients.

CONCLUSIONS

The first national anti-TB drug resistance survey in Lao PDR demonstrated an encouragingly low prevalence of MDR-TB. The results appear lower than previous WHO estimates, and in line with the routine surveillance based on Xpert MTB/RIF testing (conducted among 50% of presumptive TB patients in 2017). The country should continue to expand its Xpert MTB/RIF network and strive to achieve universal drug susceptibility testing.

Genome-wide SNP and InDel mutations in Mycobacterium tuberculosis associated with rifampicin and isoniazid resistance

OBJECTIVE

Multiple resistances to isoniazid and rifampicin lead to the majority of death associated with M. tuberculosis infection. This study aimed to characterize the single nucleotide polymorphisms (SNPs) and insertion and deletion (InDel) mutations associated with isoniazid and rifampicin resistance.

METHODS

The M. tuberculosis strain H37Rv was cultured and treated with isoniazid or rifampicin for generations. Total DNA samples from different generations were extracted for construction of DNA library, and the SNP and InDel mutation in different samples were detected by whole genome sequencing. Bioinformatics analysis such as phylogenetic tree and heap map were also performed.

RESULTS

Totally 58 nonsynonymous SNP mutations, 64 synonymous SNP mutations, and 99 SNP mutations in intergenic regions were detected in M. tuberculosis strains treated with rifampicin or isoniazid. Seven InDel mutations were found in the intergenic regions, and also six frameshift InDel mutation and three non-frameshift InDel mutations were also characterized. The phylogenetic tree showed clustering of all samples into three main subgroups. A great number of known and newly identified genes associated with drug resistance were detected in M. tuberculosis, showing distinct mutation patterns.

CONCLUSION

By whole genome sequencing, many genetic mutations in both known and new genes associated with isoniazid and rifampicin resistance were characterized in M. tuberculosis.

Rapid Microarray-Based Detection of Rifampin, Isoniazid, and Fluoroquinolone Resistance in Mycobacterium tuberculosis by Use of a Single Cartridge

The rapid and robust identification of mutations in Mycobacterium tuberculosis complex (MTBC) strains mediating multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes is crucial to combating the MDR tuberculosis (TB) epidemic. Currently available molecular anti-TB drug susceptibility tests either are restricted to a single target or drug (i.e., the Xpert MTB/RIF test) or present a risk of cross-contamination due to the design limitations of the open platform (i.e., line probe assays). With a good understanding of the technical and commercial boundaries, we designed a test cartridge based on an oligonucleotide array into which dried reagents are introduced and which has the ability to identify MTBC strains resistant to isoniazid, rifampin, and the fluoroquinolones. The melting curve assay interrogates 43 different mutations in the rifampin resistance-determining region (RRDR) of rpoB, rpoB codon 572, katG codon 315, the inhA promoter region, and the quinolone resistance-determining region (QRDR) of gyrA in a closed cartridge system within 90 min. Assay performance was evaluated with 265 clinical MTBC isolates, including MDR/XDR, non-MDR, and fully susceptible isolates, from a drug resistance survey performed in Swaziland in 2009 and 2010. In 99.5% of the cases, the results were consistent with data previously acquired utilizing Sanger sequencing. The assay, which uses a closed cartridge system in combination with a battery-powered Alere q analyzer and which has the potential to extend the current gene target panel, could serve as a rapid and robust point-of-care test in settings lacking a comprehensive molecular laboratory infrastructure to differentiate TB patients infected with MDR and non-MDR strains and to assist clinicians with their early treatment decisions.

The reliability of rifampicin resistance as a proxy for multidrug-resistant tuberculosis: a systematic review of studies from Iran

In Iran, patients showing rifampicin (RIF) resistance detected by the Xpert® MTB/RIF assay are considered as candidates for multidrug-resistant tuberculosis (MDR-TB) treatment. Despite the fact that RIF resistance has been used as a proxy for MDR-TB, little is known about the proportion of isoniazid (INH) resistance patterns in RIF-resistant TB. We systematically searched MEDLINE, Embase, and other databases up to March 2017 for studies addressing the proportion of INH resistance patterns in RIF-resistant TB in Iran. The data were pooled using a random effects model. Heterogeneity was assessed using Cochran's Q and I² statistics. A total of 11 articles met the eligibility criteria. Data analysis demonstrated that 33.3% of RIF-resistant isolates from new TB cases and 14.8% of RIF-resistant isolates from previously treated cases did not display resistance to INH. The relatively high proportion of INH susceptibility among isolates with RIF resistance indicated that RIF resistance may no longer predict MDR-TB in Iran. Therefore, the detection of RIF resistance by the Xpert MTB/RIF assay will require complementary detection of INH resistance by other drug susceptibility testing (DST) methods in order to establish the diagnosis of MDR-TB.

Discordance across Phenotypic and Molecular Methods for Drug Susceptibility Testing of Drug-Resistant Mycobacterium tuberculosis Isolates in a Low TB Incidence Country

With increasing incidence of multidrug-resistant tuberculosis (MDR-TB), accurate drug susceptibility testing (DST) of Mycobacterium tuberculosis to first-line drugs has become crucial for proper patient management. We evaluated concordance of DST results for 70 M. tuberculosis isolates across two phenotypic and two molecular methods: BACTEC 460TB, MGIT 960 system, GenoType MTBDRplus and DNA sequencing of gene segments most commonly implicated in conferring resistance to anti-TB drugs. Most (84%) M. tuberculosis isolates were multidrug-resistant. Twenty-four isolates yielded discrepant DST results. For rifampicin, isoniazid and streptomycin, 96%, 97% and 93% of isolates, respectively, were susceptible or resistant by all four methods, whereas for ethambutol, this agreement was observed for only 76% of isolates (P<0.05 for rifampicin or isoniazid or streptomycin versus ethambutol). Occurrence of rare mutations in three isolates that confer low-level resistance caused lower agreement for rifampicin among the four methods (kappa coefficient (κ) range, 0.84 to 0.95). For isoniazid, there was perfect agreement among phenotypic methods and molecular methods (κ, 1.00) but lower agreement between phenotypic and molecular methods. Three isolates were detected as polydrug-resistant by MGIT 960 system but as multidrug-resistant by DNA sequence-based method. The agreement was higher for streptomycin among the two phenotypic methods (κ, 0.97) while targeted sequencing yielded lower agreement (κ range, 0.86 to 0.89). The discrepancy for ethambutol resulted largely due to lower concordance of MGIT 960 results (κ range, 0.53 to 0.64). The MGIT 960 system is an accurate method for DST of M. tuberculosis against isoniazid and streptomycin while the results of rifampicin susceptibility should be complemented with DNA sequencing-based method when the suspicion for resistance is high. The possibility of false susceptibility to ethambutol with MGIT 960 system suggests that molecular or other phenotypic methods may be more useful when accurate ethambutol susceptibility results are warranted.

The Race Is On To Shorten the Turnaround Time for Diagnosis of Multidrug-Resistant Tuberculosis

To realize the most benefit from multidrug-resistant tuberculosis (MDR-TB) screening, all nucleic acid amplification test (NAAT)-positive respiratory specimens should be universally tested. Once an MDR-TB diagnosis is established, additional testing is warranted to provide details about the detected mutations. The lab-on-chip technology described by A. M. Cabibbe et al. (J Clin Microbiol 53:3876-3880, 2015, http://dx.doi.org/10.1128/JCM.01824-15) potentially provides this much needed information.

Evaluation of the Cepheid Xpert MTB/RIF assay

The lack of capacity to provide laboratory confirmation of a diagnosis of tuberculosis disease (TB) is contributing to enormous gaps in the ability to find, treat and follow TB patients. WHO estimates that globally only about 57% of the notified new cases of pulmonary TB in 2012 and about 19% of rifampicin-resistant TB cases were laboratory confirmed. The Cepheid Xpert(®) MTB/RIF assay has been credited with revolutionizing laboratory testing to aid in the diagnosis of TB and rifampicin-resistant TB. This semi-automated test can detect both the causative agent of TB and mutations that confer rifampicin resistance from clinical specimens within 2 h after starting the test. In this article, we review the performance of the test, its pathway to regulatory approval and endorsement, guidelines for its use and lessons learned from the implementation of the test in low-burden, high-resource countries and in high-burden, low-resource countries.

Evaluation of two line probe assays for rapid detection of Mycobacterium tuberculosis, tuberculosis (TB) drug resistance, and non-TB Mycobacteria in HIV-infected individuals with suspected TB

Limited performance data from line probe assays (LPAs), nucleic acid tests used for the rapid diagnosis of tuberculosis (TB), nontuberculosis mycobacteria (NTM), and Mycobacterium tuberculosis drug resistance are available for HIV-infected individuals, in whom paucibacillary TB is common. In this study, the strategy of testing sputum with GenoType MTBDRplus (MTBDR-Plus) and GenoType Direct LPA (Direct LPA) was compared to a gold standard of one mycobacterial growth indicator tube (MGIT) liquid culture. HIV-positive (HIV(+)) individuals with suspected TB from southern Africa and South America with <7 days of TB treatment had 1 sputum specimen tested with Direct LPA, MTBDR-Plus LPA, smear microscopy, MGIT, biochemical identification of mycobacterial species, and culture-based drug-susceptibility testing (DST). Of 639 participants, 59.3% were MGIT M. tuberculosis culture positive, of which 276 (72.8%) were acid-fast bacillus (AFB) smear positive. MTBDR-Plus had a sensitivity of 81.0% and a specificity of 100%, with sensitivities of 44.1% in AFB smear-negative versus 94.6% in AFB smear-positive specimens. For specimens that were positive for M. tuberculosis by MTBDR-Plus, the sensitivity and specificity for rifampin resistance were 91.7% and 96.6%, respectively, and for isoniazid (INH) they were 70.6% and 99.1%. The Direct LPA had a sensitivity of 88.4% and a specificity of 94.6% for M. tuberculosis detection, with a sensitivity of 72.5% in smear-negative specimens. Ten of 639 MGIT cultures grew Mycobacterium avium complex or Mycobacterium kansasii, half of which were detected by Direct LPA. Both LPA assays performed well in specimens from HIV-infected individuals, including in AFB smear-negative specimens, with 72.5% sensitivity for M. tuberculosis identification with the Direct LPA and 44.1% sensitivity with MTBDR-Plus. LPAs have a continued role for use in settings where rapid identification of INH resistance and clinically relevant NTM are priorities.

Diagnostic implications of inconsistent results obtained with the Xpert MTB/Rif assay in detection of Mycobacterium tuberculosis isolates with an rpoB mutation associated with low-level rifampin resistance

Xpert-MTB/Rif is one of the most frequently used molecular screening tests for multidrug-resistant tuberculosis worldwide. We report false-negative assay results in the presence of rpoB Leu533Pro, which is associated with low-level phenotypic rifampin resistance. Accurate and timely confirmation of rifampin susceptibility results obtained with Xpert-MTB/Rif is imperative.

Advances in tuberculosis diagnostics: the Xpert MTB/RIF assay and future prospects for a point-of-care test

Rapid progress has been made in the development of new diagnostic assays for tuberculosis in recent years. New technologies have been developed and assessed, and are now being implemented. The Xpert MTB/RIF assay, which enables simultaneous detection of Mycobacterium tuberculosis (MTB) and rifampicin (RIF) resistance, was endorsed by WHO in December, 2010. This assay was specifically recommended for use as the initial diagnostic test for suspected drug-resistant or HIV-associated pulmonary tuberculosis. By June, 2012, two-thirds of countries with a high tuberculosis burden and half of countries with a high multidrug-resistant tuberculosis burden had incorporated the assay into their national tuberculosis programme guidelines. Although the development of the Xpert MTB/RIF assay is undoubtedly a landmark event, clinical and programmatic effects and cost-effectiveness remain to be defined. We review the rapidly growing body of scientific literature and discuss the advantages and challenges of using the Xpert MTB/RIF assay in areas where tuberculosis is endemic. We also review other prospects within the developmental pipeline. A rapid, accurate point-of-care diagnostic test that is affordable and can be readily implemented is urgently needed. Investment in the tuberculosis diagnostics pipeline should remain a major priority for funders and researchers.

Performance of Cepheid ® Xpert MTB/RIF ® and TB-Biochip ® MDR in two regions of Russia with a high prevalence of drug-resistant tuberculosis

The purpose of this study was to assess the performance of Cepheid® Xpert MTB/RIF® ("Xpert") and TB-Biochip® MDR ("TB-Biochip"). Sputum specimens from adults with presumptive tuberculosis (TB) were homogenized and split for: (1) direct Xpert and microscopy, and (2) concentration for Xpert, microscopy, culture [Lowenstein-Jensen (LJ) solid media and Mycobacteria Growth Indicator Tube® (MGIT)], indirect drug susceptibility testing (DST) using the absolute concentration method and MGIT, and TB-Biochip. In total, 109 of 238 (45.8 %) specimens were culture-positive for Mycobacterium tuberculosis complex (MTBC), and, of these, 67 isolates were rifampicin resistant (RIF-R) by phenotypic DST and 64/67 (95.5 %) were isoniazid resistant (INH-R). Compared to culture of the same specimen, a single direct Xpert was more sensitive for detecting MTBC [95.3 %, 95 % confidence interval (CI), 90.0-98.3 %] than direct (59.6 %, 95 % CI, 50.2-68.5 %) or concentrated smear (85.3 %, 95 % CI, 77.7-91.1 %) or LJ culture (80.8 %, 95 % CI, 72.4-87.5 %); the specificity was 86.0 % (95 % CI, 78.9-91.3 %). Compared with MGIT DST, Xpert correctly identified 98.2 % (95 % CI, 91.5-99.9 %) of RIF-R and 95.5 % (95 % CI, 85.8-99.2 %) of RIF-susceptible (RIF-S) specimens. In a subset of 104 specimens, the sensitivity of TB-Biochip for MTBC detection compared to culture was 97.3 % (95 % CI, 91.0-99.5 %); the specificity was 78.1 % (95 % CI, 61.5-89.9 %). TB-Biochip correctly identified 100 % (95 % CI, 94.2-100 %) of RIF-R, 94.7 % (95 % CI, 76.7-99.7 %) of RIF-S, 98.2 % (95 % CI, 91.4-99.9 %) of INH-R, and 78.6 % (95 % CI, 52.1-94.2 %) of INH-S specimens compared to MGIT DST. Xpert and Biochip were similar in accuracy for detecting MTBC and RIF resistance compared to conventional culture methods.

True facets of TB diagnosis in 2012: Hypes and realities

Tuberculosis takes a heavy toll of ~5000 lives every day from the disease; responsible for the 86% of DALY burden. Despite having drugs to treat TB efficiently, we have failed to control the disease. Mycobacterium tuberculosis has exploited it to their advantage evolving with multiple mutations making it resistant to first-line and second-line drugs. Most of the high-burden countries are low-medium income countries, their national TB program (NTP) still use sputum smear microscopy as the tool of diagnosis. Many new molecular tools are emerging, but confuse the larger TB clinical scientific community at the NTPs. Coherent information need to be disseminated, encouraging TB scientific community to generate evidences within NTPs assessing new tools through critical analyses in terms of value addition and cost benefit before considering rolling out in the program. It is also imperative that the scientific community need to have an open mind to use different tools in the right permutation and combination than being exclusive of one another. This article portrays an overview of the diagnostics landscape in 2012 with pros and cons of different tools to be able to generate a step-wise algorithm for optimal exploitation of the tools within available resources in each of the settings.