Rapid Diagnosis of Tuberculosis and Multidrug Resistance by the Microscopic-Observation Drug-Susceptibility Assay

Evaluation of three alternatives cost-effective culture media for Mycobacterium tuberculosis detection and drug susceptibility determination using the microscopic observation drug susceptibility (MODS) assay

Tuberculosis phenotypic detection assays are commonly used in low-resource countries. Therefore, reliable detection methods are crucial for early diagnosis and treatment. The microscopic observation drug susceptibility (MODS) assay is a culture-based test to detect Mycobacterium tuberculosis and characterize drug resistance in 7-10 days directly from sputum. The use of MODS is limited by the availability of supplies necessary for preparing the enriched culture. In this study, we evaluated three dry culture media that are easier to produce and cheaper than the standard one used in MODS [1]: an unsterilized powder-based mixed (Boldú et al., 2007) [2], a sterile-lyophilized medium, and (Sengstake et al., 2017) [3] an irradiated powder-based mixed. Mycobacterial growth and drug susceptibility were evaluated for rifampin, isoniazid, and pyrazinamide (PZA). The alternative cultures were evaluated using 282 sputum samples with positive acid-fast smears. No significant differences were observed in the positivity test rates. The positivity time showed high correlations (Rho) of 0.925, 0.889, and 0.866 between each of the three alternative media and the standard. Susceptibility testing for MDR and PZA showed an excellent concordance of 1 compared to the reference test. These results demonstrate that dry culture media are appropriate and advantageous for use in MODS in low-resource settings.

Clinically encountered growth phenotypes of tuberculosis-causing bacilli and their in vitro study: A review

The clinical manifestations of tuberculosis (TB) vary widely in severity, site of infection, and outcomes of treatment—leading to simultaneous efforts to individualize therapy safely and to search for shorter regimens that can be successfully used across the clinical spectrum. In these endeavors, clinicians and researchers alike employ mycobacterial culture in rich media. However, even within the same patient, individual bacilli among the population can exhibit substantial variability in their culturability. Bacilli in vitro also demonstrate substantial heterogeneity in replication rate and cultivation requirements, as well as susceptibility to killing by antimicrobials. Understanding parallels in clinical, ex vivo and in vitro growth phenotype diversity may be key to identifying those phenotypes responsible for treatment failure, relapse, and the reactivation of bacilli that progresses TB infection to disease. This review briefly summarizes the current role of mycobacterial culture in the care of patients with TB and the ex vivo evidence of variability in TB culturability. We then discuss current advances in in vitro models that study heterogenous subpopulations within a genetically identical bulk culture, with an emphasis on the effect of oxidative stress on bacillary cultivation requirements. The review highlights the complexity that heterogeneity in mycobacterial growth brings to the interpretation of culture in clinical settings and research. It also underscores the intricacies present in the interplay between growth phenotypes and antimicrobial susceptibility. Better understanding of population dynamics and growth requirements over time and space promises to aid both the attempts to individualize TB treatment and to find uniformly effective therapies.

Review and Updates on the Diagnosis of Tuberculosis

Diagnosis of tuberculosis, and especially the diagnosis of extrapulmonary tuberculosis, still faces challenges in clinical practice. There are several reasons for this. Methods based on the detection of Mycobacterium tuberculosis (Mtb) are insufficiently sensitive, methods based on the detection of Mtb-specific immune responses cannot always differentiate active disease from latent infection, and some of the serological markers of infection with Mtb are insufficiently specific to differentiate tuberculosis from other inflammatory diseases. New tools based on technologies such as flow cytometry, mass spectrometry, high-throughput sequencing, and artificial intelligence have the potential to solve this dilemma. The aim of this review was to provide an updated overview of current efforts to optimize classical diagnostic methods, as well as new molecular and other methodologies, for accurate diagnosis of patients with Mtb infection.

Molecular Epidemiology and Polymorphism Analysis in Drug-Resistant Genes in M. tuberculosis Clinical Isolates from Western and Northern India

Introduction

The mechanistic details of first line drug (FLD) resistance have been thoroughly explored but the genetic resistance mechanisms of second line injectables, which form the backbone of the combinatorial drug resistant tuberculosis therapy, are partially identified. This study aims to highlight the genetic and spoligotypic differences in the second line drug (SLD) resistant and sensitive Mycobacterium tuberculosis (Mtb) clinical isolates from Mumbai (Western India) and Lucknow (Northern India).

Methods

The rrs, eis, whiB7, tlyA, gyrA and gyrB target loci were screened in 126 isolates and spoligotyped.

Results

The novel mutations were observed in whiB7 loci (A43T, C44A, C47A, G48T, G59A and T152G in 5’-UTR; A42C, C253T and T270G in gene), tlyA (+CG200, G165A, C415G, and +G543) and gyrB (+G1359 and +A1429). Altogether, the rrs, eis, and whiB7 loci harbored mutations in ~86% and ~47% kanamycin resistant isolates from Mumbai and Lucknow, respectively. Mumbai strains displayed higher prevalence of mutations in gyrA (~85%) and gyrB loci (~13%) as compared to those from Lucknow (~69% and ~3.0%, respectively). Further, spoligotyping revealed that Beijing lineage is distributed equally amongst the drug resistant strains of Mumbai and Lucknow, but EAI-5 is existed at a higher level only in Mumbai. The lineages Manu2, CAS1-Delhi and T1 are more prevalent in Lucknow.

Conclusion

Besides identifying novel mutations in whiB7, tlyA and gyrB target loci, our analyses unveiled a potential polymorphic and phylogeographical demarcation among two distinct regions.

Determining the Prevalence of Rifampicin Resistant Tuberculosis in A Tertiary Care Centre of North India by using Rapid Culture Method and Gene Xpert

The objective of the present study is to find the prevalence of Mycobacterium tuberculosis from respiratory samples like sputum, BAL and pleural fluid, compare conventional LJ culture with rapid culture method i.e Mycobacterium growth indicator tube (MGIT) and to determine the pattern of drug resistance by automated methods i.e Gene Xpert. Respiratory samples were collected in sterile, wide-mouth, disposable, leak proof containers without any preservatives. Specimens were inoculated into MGIT for primary isolation of Mycobacteria. The specimen was processed according to the SOP manual provided by Becton Dickinson Company. The tubes were read for increasing fluorescence by MGIT reader. Reported results only when a MGIT tube was positive by the MGIT reader and smear made from the positive broth is also positive for AFB. For further identification, TBcID card test was put from MGIT positive tube and the result was given accordingly as mentioned in the procedure for TBcID kit insert. Polymerase chain reaction (PCR) was done in all 17 positive cases. The drug sensitivity test (CB-NAAT) was done at State Intermediate Reference Laboratory, Chandan Nagar, Dehradun, Uttrakhand as per RNTCP laboratory operational guidelines. In our study total number of samples received from the clinically suspected cases of pulmonary tuberculosis were 156, out of which 11% were positive and 89% were negative. The predominant age group involved was 51-60 years 24%, followed by 61-70 years 22%. In young children and adolescent age group very less number of samples were received i.e. 0-5%. Out of 17 positive samples, 94.11% (16/17) were detected as sensitive for Rifampicin and 5.89% (1/17) were resistant. On the statistical analysis of our data for MGIT, Positive Predictive Value (PPV) was 29% against Negative Predictive Value (NPV) of 100%. The specificity of MGIT was 92% against a sensitivity of 100%. Culture is still needed for species identification, confirmation and drug susceptibility testing. The diagnostic superiority of MGIT, both in terms of sensitivity and specificity has been proven better as compared to LJ in previous other studies and supported by our study as well. In our study, the diagnostic efficacy of MGIT culture was found to be superior as compared to the conventional LJ culture. The positivity rate was 10.89% (17/156) in MGIT & 3.2% (5/156) in LJ culture.

Neoteric advancements in TB diagnostics and its future frame

Tuberculosis (TB) is one of the major infectious disease that causes threat to human health and leads to death in most of the cases. Mycobacterium tuberculosis is the causative agent that can affect both pulmonary and extra pulmonary regions of the body. This infection can be presented either as an active or latent form in the patients. Although this disease has been declared curable and preventable by WHO, it still holds its position as a global emergency. Over the past decade many hurdles such as low immunity, co-infections like HIV, autoimmune disorders, poverty, malnutrition and emerging trends in drug resistance patterns are hindering the eradication of this infection. However, many programmes have been launched by WHO with involvement of governments at various level to put a full stop over the disease. Under the Revised National Tuberculosis Control Programme (RNTCP) which was recently renamed as National Tuberculosis Elimination Programme (NTEP), the major focus is on eliminating tuberculosis by the year 2025. The main aim of the programme is to identify feasible quality testing, evaluate through NIKSHYA poshak yozana, restrict through BCG vaccination and assemble with public awareness to eradicate MTB. Numerous novel diagnostic techniques and molecular tools have been developed to elucidate and differentiate report of various suspected and active tuberculosis patients. However, improvements are still required to cut short the duration of the overall process ranging from screening of patients to their successful treatment.

Delayed Isolation of Active Pulmonary Tuberculosis in Hospitalized Patients: A Pivotal Role of Radiologic Evaluation

OBJECTIVE. The purpose of this study was to determine factors related to delayed isolation of patients hospitalized with active pulmonary tuberculosis (TB). MATERIALS AND METHODS. A total of 130 immunocompetent hospitalized patients with active pulmonary TB who had positive sputum culture results from January 2015 to December 2017 were reviewed. Delayed isolation of pulmonary TB was defined as failure to initiate airborne isolation within the first 3 days of hospitalization. Clinical and microbiologic characteristics of the patients and radiologic features on chest radiography (n = 130) and chest CT (n = 118) were retrospectively reviewed. Findings were compared between patients with early isolation and those with delayed isolation. Univariate and multivariate analyses were performed to determine independent predictors of delayed isolation. RESULTS. Forty-four patients (34%) had delayed isolation after initial hospitalization. On univariate and multivariate analyses, atypical presentation of active pulmonary TB on CT (odds ratio, 7.203; 95% CI, 2.203-23.551; p = 0.001) and concurrent lung parenchymal diseases on CT (odds ratio, 14.605; 95% CI, 3.274-65.155; p < 0.001) were significant predictors of delayed isolation of patients with active pulmonary TB. CONCLUSION. Awareness of the factors related to delayed diagnosis of active pulmonary TB is important to avoid an unexpected in-hospital outbreak of TB and control the disease. Atypical presentation of active pulmonary TB and concurrent lung parenchymal diseases on CT are significant factors related to delayed isolation of hospitalized patients with active pulmonary TB.

Direct Determination of Pyrazinamide (PZA) Susceptibility by Sputum Microscopic Observation Drug Susceptibility (MODS) Culture at Neutral pH: the MODS-PZA Assay

Pyrazinamide (PZA) is considered the pivot drug in all tuberculosis treatment regimens due to its particular action on the persistent forms of Mycobacterium tuberculosis. However, no drug susceptibility test (DST) is considered sufficiently reliable for routine application. Although molecular tests are endorsed, their application is limited to known PZA resistance associated mutations. Microbiological DSTs for PZA have been restricted by technical limitations, especially the necessity for an acidic pH.

Pyrazinamide (PZA) is considered the pivot drug in all tuberculosis treatment regimens due to its particular action on the persistent forms of Mycobacterium tuberculosis. However, no drug susceptibility test (DST) is considered sufficiently reliable for routine application. Although molecular tests are endorsed, their application is limited to known PZA resistance associated mutations. Microbiological DSTs for PZA have been restricted by technical limitations, especially the necessity for an acidic pH. Here, for the first time, MODS culture at neutral pH was evaluated using high PZA concentrations (400 and 800 μg/ml) to determine PZA susceptibility directly from sputum samples. Sputum samples were cultured with PZA for up to 21 days at 37°C. Plate reading was performed at two time points: R1 (mean, 10 days) and R2 (mean, 13 days) for each PZA concentration. A consensus reference test, composed of MGIT-PZA, pncA sequencing, and the classic Wayne test, was used. A total of 182 samples were evaluated. The sensitivity and specificity for 400 μg/ml ranged from 76.9 to 89.7 and from 93.0 to 97.9%, respectively, and for 800 μg/ml ranged from 71.8 to 82.1 and from 95.8 to 98.6%, respectively. Compared to MGIT-PZA, our test showed a similar turnaround time (medians of 10 and 12 days for PZA-sensitive and -resistant isolates, respectively). In conclusion, MODS-PZA is presented as a fast, simple, and low-cost DST that could complement the MODS assay to evaluate resistance to the principal first-line antituberculosis drugs. Further optimization of test conditions would be useful in order to increase its performance.

Non-commercial phenotypic assays for the detection of Mycobacterium tuberculosis drug resistance: a systematic review

Several rapid non-commercial culture-based methods and assays for drug susceptibility testing (DST) of Mycobacterium tuberculosis have emerged over the last decades. The aim of the current review was to summarise evidence on the performance of microscopic observation of drug susceptibility (MODS), thin-layer agar (TLA) and colorimetric redox-indicator (CRI) assays for detection of resistance to first- and second-line anti-tuberculosis (TB) drugs. Forty-three publications satisfying selection criteria were selected for data extraction. MODS and CRI assays demonstrated pooled sensitivity and specificity of > 93% for the detection of resistance to rifampicin and isoniazid and confirmed their utility for an accurate detection of multidrug-resistant TB (MDR-TB) in various settings. Sensitivity and specificity values for indirect DST for ethambutol (EMB) using CRI assays were 94.0% and 82.0%, respectively, suggesting that CRIs could be used to rule out resistance to EMB. Performance for other drugs varied more substantially across the reports. There was no sufficient evidence on the performance of the TLA assay for making any conclusion on its utility for DST. Our data suggests that non-commercial assays could be used for a rapid and accurate DST in settings where the use of commercial World Health Organization-endorsed assays could be limited due to a variety of reasons including limited resources, laboratory facilities or trained personnel. While inexpensive and easy-to-perform MODS and TLA assays can be used in low-income settings, using CRI assays for determination of minimal inhibitory concentrations may be implemented in middle- and high-income countries with high MDR-TB burden to guide clinical management of TB patients.

MODS-Wayne, a Colorimetric Adaptation of the Microscopic-Observation Drug Susceptibility (MODS) Assay for Detection of Mycobacterium tuberculosis Pyrazinamide Resistance from Sputum Samples

Although pyrazinamide (PZA) is a key component of first- and second-line tuberculosis treatment regimens, there is no gold standard to determine PZA resistance. Approximately 50% of multidrug-resistant tuberculosis (MDR-TB) and over 90% of extensively drug-resistant tuberculosis (XDR-TB) strains are also PZA resistant.

Although pyrazinamide (PZA) is a key component of first- and second-line tuberculosis treatment regimens, there is no gold standard to determine PZA resistance. Approximately 50% of multidrug-resistant tuberculosis (MDR-TB) and over 90% of extensively drug-resistant tuberculosis (XDR-TB) strains are also PZA resistant. pncA sequencing is the endorsed test to evaluate PZA susceptibility. However, molecular methods have limitations for their wide application. In this study, we standardized and evaluated a new method, MODS-Wayne, to determine PZA resistance. MODS-Wayne is based on the detection of pyrazinoic acid, the hydrolysis product of PZA, directly in the supernatant of sputum cultures by detecting a color change following the addition of 10% ferrous ammonium sulfate. Using a PZA concentration of 800 µg/ml, sensitivity and specificity were evaluated at three different periods of incubation (reading 1, reading 2, and reading 3) using a composite reference standard (MGIT-PZA, pncA sequencing, and the classic Wayne test). MODS-Wayne was able to detect PZA resistance, with a sensitivity and specificity of 92.7% and 99.3%, respectively, at reading 3. MODS-Wayne had an agreement of 93.8% and a kappa index of 0.79 compared to the classic Wayne test, an agreement of 95.3% and kappa index of 0.86 compared to MGIT-PZA, and an agreement of 96.9% and kappa index of 0.90 compared to pncA sequencing. In conclusion, MODS-Wayne is a simple, fast, accurate, and inexpensive approach to detect PZA resistance, making this an attractive assay especially for low-resource countries, where TB is a major public health problem.

Integrated Tuberculosis/Human Immunodeficiency Virus Community-Based Case Finding in Rural South Africa: Implications for Tuberculosis Control Efforts

Background

Intensive case finding is endorsed for tuberculosis (TB) control in high-risk populations. Novel case-finding strategies are needed in hard-to-reach rural populations with high prevalence of TB and human immunodeficiency virus (HIV).

Methods

We performed community-based integrated HIV and TB intensive case finding in a rural South African subdistrict from March 2010 to June 2012. We offered TB symptom screening, sputum collection for microbiologic diagnosis, rapid fingerstick HIV testing, and phlebotomy for CD4 cell count. We recorded number of cases detected and calculated population-level rates and number needed to screen (NNS) for drug-susceptible and -resistant TB.

Results

Among 5615 persons screened for TB at 322 community sites, 91.2% accepted concurrent HIV testing, identifying 510 (9.9%) HIV-positive individuals with median CD4 count of 382 cells/mm³ (interquartile range = 260–552). Tuberculosis symptoms were reported by 2049 (36.4%), and sputum was provided by 1033 (18.4%). Forty-one (4.0%) cases of microbiologically confirmed TB were detected for an overall case notification rate of 730/100000 (NNS = 137); 11 (28.6%) were multidrug-resistant or extensively drug-resistant TB. Only 5 (12.2%) TB cases were HIV positive compared with an HIV coinfection rate of 64% among contemporaneously registered TB cases (P = .001).

Conclusion

Community-based integrated intensive case finding is feasible and is high yield for drug-susceptible and -resistant TB and HIV in rural South Africa. Human immunodeficiency virus–negative tuberculosis predominated in this community sample, suggesting a distinct TB epidemiology compared with cases diagnosed in healthcare facilities. Increasing HIV/TB integrated community-based efforts and other strategies directed at both HIV-positive and HIV-negative tuberculosis may contribute to TB elimination in high TB/HIV burden regions.

Microscopic observation drug-susceptibility assay vs. Xpert® MTB/RIF for the diagnosis of tuberculosis in a rural African setting: a cost-utility analysis

OBJECTIVE

To compare the cost-utility of microscopic observation drug-susceptibility assay (MODS) and Xpert^® MTB/RIF implementation for tuberculosis (TB) diagnosis in rural northern Mozambique.

METHODS

Stochastic transmission compartmental TB model from the healthcare provider perspective with parameter input from direct measurements, systematic literature reviews and expert opinion. MODS and Xpert^® MTB/RIF were evaluated as replacement test of smear microscopy (SM) or as an add-on test after a negative SM. Costs were calculated in 2013 USD, effects in disability-adjusted life years (DALY). Willingness to pay threshold (WPT) was established at once the per capita Gross National Income of Mozambique.

RESULTS

MODS as an add-on test to negative SM produced an incremental cost-effectiveness ratio (ICER) of 5647.89USD/DALY averted. MODS as a substitute for SM yielded an ICER of 5374.58USD/DALY averted. Xpert^® MTB/RIF as an add-on test to negative SM yielded ICER of 345.71USD/DALY averted. Xpert^® MTB/RIF as a substitute for SM obtained an ICER of 122.13USD/DALY averted. TB prevalence and risk of infection were the main factors impacting MODS and Xpert^® MTB/RIF ICER in the one-way sensitivity analysis. In the probabilistic sensitivity analysis, Xpert^® MTB/RIF was most likely to have an ICER below the WPT, whereas MODS was not.

CONCLUSION

Our cost-utility analysis favours the implementation of Xpert^® MTB/RIF as a replacement of SM for all TB suspects in this rural high TB/HIV prevalence African setting.

Concurrent evaluation of microscopic observation of drug susceptibility assay for pulmonary and extrapulmonary tuberculosis

BACKGROUND:

Methods for detection and drug susceptibility of tuberculosis (TB) with solid media are inexpensive but slow and laborious. Rapid methods to diagnose TB and multidrug-resistant TB (MDR-TB) are a global priority for TB control.

OBJECTIVES:

A study was performed to compare the sensitivity of detection of mycobacterial growth and time of culture positivity by microscopic observation of drug susceptibility (MODS) assay with that of Lowenstein–Jensen (LJ) culture in pulmonary and extrapulmonary TB and to evaluate the concordance of the susceptibilities to isoniazid (INH) and rifampicin (RIF) by MODS and proportion method on LJ.

MATERIALS AND METHODS:

A prospective, laboratory-based study was conducted on a total of 300 samples from suspected cases of pulmonary and extrapulmonary TB. Samples were inoculated on LJ medium as per the standard guidelines and MODS assay was performed.

RESULTS:

Sensitivity of MODS assay was 80% and 83.3% and specificity was 92.9% and 83.3% for pulmonary and extrapulmonary samples, respectively. Difference between mean time to detection of Mycobacterium TB (MTB) by LJ medium and MODS was statistically significant, with MODS being faster. drug susceptibility testing (DST) by MODS when compared to economic variant of proportion method was 87.87% for RIF, 90.9% for INH, and 96.96% for MDR-TB detection.

CONCLUSION:

MODS assay provides rapid, safe, and sensitive detection of TB faster than the existing gold standard. It is extremely promising in effectively diagnosing MDR-TB.

Drug resistance pattern of mycobacterial isolates in HIV and non-HIV population in South India

Background:

Emergence of drug resistance has complicated the treatment of tuberculosis (TB). WHO reports India to be one among 27 “high burden” multidrug-resistant (MDR) TB countries.

Objective:

To diagnose TB and detect drug resistance of mycobacterial isolates in acid-fast bacilli (AFB) smear negative HIV reactive patients (Group A) and compare them with HIV seropositive AFB smear positive (Group B) and HIV-seronegative AFB positive cases (Group C).

Materials and Methods:

Clinical specimens collected in all groups were processed as per the standard protocol except blood, which was processed by lysis centrifugation technique. They were then inoculated with Lowenstein-Jensen media and the isolates obtained were subjected to drug susceptibility test (DST) by proportion method and genotype MTBDR plus assay.

Results:

In Group A, 162 patients were included. Of the 443 clinical samples collected, 76 mycobacterial strains were obtained from 67 (41%) patients. Of these, 50 (65.8%) were sensitive to all drugs and 26 (34.2%) resistant to one or more anti-tubercular drugs. Antibiogram of Group A when compared with Group B and C showed that the MDR rate 6.6%, 6.7% and 8% respectively) did not differ much; but resistance to at least single drug was (26 [34.2%], 3 [10%], and 8 [16%]), respectively.

Conclusion:

Our study suggests that HIV has no influence on the anti-tubercular resistance pattern, but increased MDR rate along with HIV in high TB burden setting stresses the need for early diagnosis and DST in providing proper regimens and improve prognosis.

Evaluation of the microscopic observation drug susceptibility assay for the rapid detection of MDR-TB and XDR-TB in China: a prospective multicentre study

OBJECTIVES

To perform a multicentre study evaluating the performance of the microscopic observation drug susceptibility (MODS) assay for the detection of MDR-TB and XDR-TB in high-burden resource-limited settings.

METHODS

We performed a prospective diagnostic accuracy study of drug-resistant TB suspects from outpatient and inpatient settings in five laboratories in China. Sputum was tested by smear microscopy, liquid [mycobacterial growth indicator tube (MGIT)] culture and the MODS assay at each site. Drug susceptibility testing (DST) was by MODS and an indirect 1% proportion method. The reference standard for Mycobacterium tuberculosis detection was growth on MGIT culture; the 1% proportion method was the reference standard for rifampicin, isoniazid, ofloxacin, kanamycin and capreomycin DST.

RESULTS

M. tuberculosis was identified by reference standard culture among 213/532 (40.0%) drug-resistant TB suspects. Overall MODS sensitivity for M. tuberculosis detection was 87.8%-94.3% and specificity was 96.8%-100%. For drug-resistant TB diagnosis, excellent agreement was obtained for all drugs tested at the majority of sites. The accuracy was 87.1%-96.7% for rifampicin, 87.1%-93.3% for isoniazid, 92.7%-100% for ofloxacin, 90.9%-100% for kanamycin and 90.2%-100% for capreomycin. The median time to culture positivity was significantly shorter for MODS than for the MGIT liquid culture (8 days versus 11 days, P<0.001). The contamination rate ranged between 2.1% and 5.3%.

CONCLUSIONS

In the study settings, MODS provided high sensitivity and specificity for rapid diagnosis of TB and drug-resistant TB. We consider it to have a strong potential for timely detection of MDR-TB and XDR-TB in high-burden resource-limited settings.

A field evaluation of the Hardy TB MODS Kit™ for the rapid phenotypic diagnosis of tuberculosis and multi-drug resistant tuberculosis

Background

Even though the WHO-endorsed, non-commercial MODS assay offers rapid, reliable TB liquid culture and phenotypic drug susceptibility testing (DST) at lower cost than any other diagnostic, uptake has been patchy. In part this reflects misperceptions about in-house assay quality assurance, but user convenience of one-stop procurement is also important. A commercial MODS kit was developed by Hardy Diagnostics (Santa Maria, CA, USA) with PATH (Seattle, WA, USA) to facilitate procurement, simplify procedures through readymade media, and enhance safety with a sealing silicone plate lid. Here we report the results from a large-scale field evaluation of the MODS kit in a government service laboratory.

Methods & Findings

2446 sputum samples were cultured in parallel in Lowenstein-Jensen (LJ), conventional MODS and in the MODS kit. MODS kit DST was compared with conventional MODS (direct) DST and proportion method (indirect) DST. 778 samples (31.8%) were Mycobacterium tuberculosis culture-positive. Compared to conventional MODS the sensitivity, specificity, positive, and negative predictive values (95% confidence intervals) of the MODS Kit were 99.3% (98.3–99.8%), 98.3% (97.5–98.8%), 95.8% (94.0–97.1%), and 99.7% (99.3–99.9%). Median (interquartile ranges) time to culture-positivity (and rifampicin and isoniazid DST) was 10 (9–13) days for conventional MODS and 8.5 (7–11) for MODS Kit (p<0.01). Direct rifampicin and isoniazid DST in MODS kit was almost universally concordant with conventional MODS (97.9% agreement, 665/679 evaluable samples) and reference indirect DST (97.9% agreement, 687/702 evaluable samples).

Conclusions

MODS kit delivers performance indistinguishable from conventional MODS and offers a convenient, affordable alternative with enhanced safety from the sealing silicone lid. The availability in the marketplace of this platform, which conforms to European standards (CE-marked), readily repurposed for second-line DST in the near future, provides a fresh opportunity for improving equity of access to TB diagnosis and first and second-line DST in settings where the need is greatest.

Microscopic observation drug susceptibility assay for the diagnosis of TB and MDR-TB in HIV-infected patients: a systematic review and meta-analysis

The objective of the present study was to assess the diagnostic accuracy of the microscopic observation drug susceptibility (MODS) assay for tuberculosis (TB) diagnosis in HIV-infected patients. MEDLINE, EMBASE, LILACS, the Cochrane Central Register of Controlled Trials, African Index Medicus, ResearchGate, SciELO, and the abstracts of the main conferences on infectious diseases and tropical medicine were searched, and other sources investigated. Only studies including HIV-infected patients evaluating MODS for the diagnosis of TB and using culture-based diagnostic tests as a gold standard were analysed. Summary sensitivity and specificity were calculated with a bivariate model. 3259 citations were found, 29 were selected for full-text review and 10 studies including 3075 samples were finally analysed. Overall diagnostic accuracy of MODS for the diagnosis of TB was a sensitivity of 88.3% (95% CI 86.18-90.2%) and specificity 98.2% (95% CI 97.75-98.55%). For multidrug-resistant (MDR)-TB, sensitivity was 89% (95% CI 66.07-97%) and specificity was 100% (95 CI 94.81-100%). For smear-negative pulmonary TB, a sensitivity of 88.2% (95% CI 86.1-89.9%) and specificity of 98.2% (95% CI 96.8-98.9%) were found. Costs varied between USD 0.72 and 7.31 per sample. Mean time to positivity was 8.24 days. MODS was found to have a good accuracy for the diagnosis of TB and MDR-TB in HIV-infected patients with low cost and fast results.

[The new tools of microbiological diagnosis of tuberculosis]

This review focuses on the role of new tools in the "modern" microbiological diagnosis of tuberculosis. Traditional techniques of microscopy and culture remain essential to diagnostic certainty, but some innovations replace daily the older techniques such as the identification of Mycobacterium tuberculosis complex by immunochromatography or mass spectrometry MALDI-TOF type from positive cultures, or susceptibility testing in liquid medium. New tools that use molecular techniques have become important. They all have in common to optimize the fight against tuberculosis by reducing diagnostic delay. They also allow rapid detection of drug resistance. However, the techniques of gene amplification directly from clinical samples are still less sensitive than culture. Bacteriological diagnosis of tuberculosis disease therefore still relies on the complementarities of different phenotypic and molecular techniques.

Optimization of the microscopic observation drug susceptibility assay for four first-line drugs using Mycobacterium tuberculosis reference strains and clinical isolates

OBJECTIVE

The aim of this study is to determine the appropriate cut-off value and turnaround time of the microscopic observation drug susceptibility assay (MODS) for isoniazid (INH), rifampicin (RMP), streptomycin (STR), and ethambutol (EMB).

DESIGN

A total of 39 Mycobacterium tuberculosis strains with confirmed drug susceptibility (reference strains) were tested with a range of drug concentrations to determine the optimal cut-off values for INH, RMP, STR, and EMB by MODS. Standard drug susceptibility testing (DST) results were evaluated relative to the Löwenstein-Jensen (L-J) proportion method. Following which, the performance of MODS was evaluated again using 36 sputum samples from patients with tuberculosis (TB) using the cut-off values determined in the aforementioned process.

RESULTS

With 39 reference strains, DST identified the following cut-off values: 0.8μg/ml INH (sensitivity, 96.0%; specificity, 92.9%), 2.0μg/ml RMP (sensitivity, 100%; specificity, 95.5%), 4.0μg/ml STR (sensitivity, 90.5%; specificity, 93.8%), and 4.0μg/ml EMB (sensitivity, 100%; specificity, 91.7%). When these cut-off values were used to analyze the 36 clinical isolates, the sensitivity and specificity of MODS were 100% and 93.1% for INH, 100% and 93.8% for RMP, 87.5% and 96.4% for STR, and 100% and 88.2% for EMB, respectively. The turnaround time for these clinical specimens was 9.0days by MODS (95% CI: 5.3-12.7), compared with 11.7days (95% CI: 9.5-13.9) for smear negative specimens.

CONCLUSION

Our study identified the optimal cut-off values of the four first-line drugs for MODS based on a wide concentration range. With the optimal cut-off values determined in this study, MODS showed high discriminatory efficiency for DST. This study also demonstrated that MODS is useful for rapid diagnosis of drug-resistant TB even for a smear negative specimen, despite the fact that it generally uses smear positive specimens as direct DST.

Meta-analysis to compare the accuracy of GeneXpert, MODS and the WHO 2007 algorithm for diagnosis of smear-negative pulmonary tuberculosis

BACKGROUND

Smear-negative pulmonary tuberculosis (SN-PTB), which is common in HIV-infected patients, is difficult to diagnose using smear microscopy alone. In 2007, the WHO developed an algorithm to improve the diagnosis and management of smear-negative tuberculosis in HIV prevalent and resource constrained settings. Implementation of the algorithm required individuals with presumptive TB to be initially evaluated using two sputum microscopy examinations followed by clinical diagnosis that may include chest X-ray and antibiotic treatment in smear-negative individuals. Since that time, the WHO has endorsed several new tests for diagnosis of tuberculosis. However, it is unclear how the new tests perform when compared to the WHO 2007 algorithm in diagnosis of SN-PTB. Using meta-analysis study design, we summarized and compared the accuracy of Xpert® MTB/Rif assay (GeneXpert) and Microscopic Observation Drug Susceptibility assay (MODS), with the WHO 2007 algorithm in the diagnosis of SN-PTB.

METHODS

A systematic review and meta-analysis of publications on GeneXpert, or MODS, or the WHO 2007 algorithm for diagnosis of SN-PTB, using culture as reference test was performed. Meta-Disc software was used to obtain pooled sensitivity and specificity of the diagnostic methods. Heterogeneity in the accuracy estimates was tested by reviewing the generated forest plots, sROC curves and the Spearman correlation coefficient of the logit of true positive rate versus the logit of false positive rate.

RESULTS

Twenty-four publications on all three diagnostic methods were meta-analyzed. The pooled sensitivity and specificity for detection of smear-negative pulmonary tuberculosis were 67% and 98% for GeneXpert, 73% and 91% for MODS, and 61% and 69% for WHO 2007 algorithm, respectively. The sensitivity of GeneXpert reduced from 67% to 54% when sub-group analysis of studies with patient HIV prevalence ≥ 30% was performed.

CONCLUSION

The GeneXpert, MODS, and the WHO algorithm have moderate to high accuracy for the diagnosis of SN-PTB. However, the accuracy of the tests is extremely variable. The setting and context under which the tests are conducted in addition to several other factors could explain this variability. There is therefore need to investigate these factors further. The information from these studies would inform the adoption and placement of these new tests.

Microscopic-observation drug-susceptibility assay for the diagnosis of drug-resistant tuberculosis in Harare, Zimbabwe

Introduction

Limited data exist on use of the microscopic-observation drug-susceptibility (MODS) assay among persons suspected of MDR-TB living in high HIV-prevalence settings.

Methods

We retrospectively reviewed available clinical and drug susceptibility data for drug-resistant TB suspects referred for culture and drug-susceptibility testing between April 1, 2011 and March 1, 2012. The diagnostic accuracy of MODS was estimated against a reference standard including Löwenstein-Jensen (LJ) media and manual liquid (BACTEC MGIT) culture. The accuracy of MODS drug-susceptibility testing (DST) was assessed against a reference standard absolute concentration method.

Results

One hundred thirty-eight sputum samples were collected from 99 drug-resistant TB suspects; in addition, six previously cultured MDR isolates were included for assessment of DST accuracy. Among persons with known HIV infection status, 39/59 (66%) were HIV-infected. Eighty-six percent of patients had a history of prior TB treatment, and 80% of individuals were on antituberculous treatment at the time of sample collection. M. tuberculosis was identified by reference standard culture among 34/98 (35%) MDR-TB suspects. Overall MODS sensitivity for M. tuberculosis detection was 85% (95% CI, 69–95%) and specificity was 93% (95% CI, 84–98%); diagnostic accuracy did not significantly differ by HIV infection status. Median time to positivity was significantly shorter for MODS (7 days; IQR 7–15 days) than MGIT (12 days; IQR 6–16 days) or LJ (28 days; IQR 21–35 days; p<0.001). Of 33 specimens with concurrent DST results, sensitivity of the MODS assay for detection of resistance to isoniazid, rifampin, and MDR-TB was 88% (95% CI, 68–97%), 96% (95% CI, 79–100%), and 91% (95% CI, 72–99%), respectively; specificity was 89% (95% CI, 52–100%), 89% (95% CI, 52–100%), and 90% (95% CI, 56–100%), respectively.

Conclusion

In a high HIV-prevalence setting, MODS diagnosed TB and drug-resistant TB with high sensitivity and shorter turnaround time compared with standard culture and DST methods.

The future of molecular diagnostics for drug-resistant tuberculosis

The last decade has seen significant advances in tuberculosis diagnostics and drug susceptibility testing (DST). During the same time period the prevalence of drug-resistant tuberculosis has increased and therefore it has become critical to understand DST for medications used to treat multidrug-resistant and extensively drug-resistant tuberculosis. This review describes recent molecular diagnostic advances for DST. Recommendations are provided for clinicians interpreting molecular DST and we describe potential opportunities for the field.

Update in tuberculosis and nontuberculous mycobacterial disease 2011

The number of tuberculosis (TB) cases and global TB incidence rates is decreasing according to the latest World Health Organization Global Tuberculosis Report (1). This is very welcome news. However, the 8.8 million incident cases of TB, 1.1 million deaths from TB among HIV-negative people, the 350,000 deaths from HIV-associated TB, and the millions of children orphaned as a result of parental deaths caused by TB provide a stark reminder of the magnitude of devastation caused by TB each year. Advances in understanding TB epidemiology diagnosis and treatment in 2011, many of which were reported in the Journal, provide hope that the annual decline in TB cases will accelerate.

BCG-specific IgG-secreting peripheral plasmablasts as a potential biomarker of active tuberculosis in HIV negative and HIV positive patients

Background

Diagnosis of active tuberculosis (TB) among sputum-negative cases, patients with HIV infection and extra-pulmonary TB is difficult. In this study, assessment of BCG-specific IgG-secreting peripheral plasmablasts, was used to identify active TB in these high-risk groups.

Methods

Peripheral blood mononuclear cells were isolated from patients with TB and controls and cultured in vitro using an assay called Antibodies in Lymphocyte Supernatant, which measures spontaneous IgG antibody release from migratory plasmablasts. A BCG-specific ELISA and flow cytometry were used to quantify in vivo activated plasmablasts in blood samples from Ethiopian subjects who were HIV negative or HIV positive. Patients diagnosed with different clinical forms of sputum-negative active TB or other diseases (n=96) were compared with asymptomatic individuals including latent TB and non-TB controls (n=85). Immunodiagnosis of TB also included the tuberculin skin test and the interferon (IFN)-γ release assay, QuantiFERON.

Results

This study demonstrated that circulating IgG+ plasmablasts and spontaneous secretion of BCG-specific IgG antibodies were significantly higher in patients with active TB compared with latent TB cases and non-TB controls. BCG-specific IgG titres were particularly high among patients coinfected with TB and HIV with CD4 T-cell counts <200 cells/ml who produced low levels of Mycobacterium tuberculosis-specific IFNγ in vitro.

Conclusions

These results suggest that BCG-specific IgG-secreting peripheral plasmablasts could be successfully used as a host-specific biomarker to improve diagnosis of active TB, particularly in people who are HIV positive, and facilitate administration of effective treatment to patients. Elevated IgG responses were associated with impaired peripheral T-cell responses, including reduced T-cell numbers and low M tuberculosis-specific IFNγ production.

Evaluation of the microscopic observational drug susceptibility assay for rapid and efficient diagnosis of multi-drug resistant tuberculosis

PURPOSE

Tuberculosis (TB) is endemic in India and the burden of multi-drug-resistant tuberculosis (MDR-TB) is high. Early detection of MDR-TB is of primary importance in controlling the spread of TB. The microscopic observational drug susceptibility (MODS) assay has been described as a cost-effective and rapid method by which mycobacterial culture and the drug susceptibility test (DST) can be done at the same time.

MATERIALS AND METHODS

A total of 302 consecutive sputum samples that were received in an accredited mycobacteriology laboratory for conventional culture and DST were evaluated by the MODS assay.

RESULTS

In comparison with conventional culture on Lowenstein Jensen (LJ) media, the MODS assay showed a sensitivity of 94.12% and a specificity of 89.39% and its concordance with the DST by the proportion method on LJ media to isoniazid and rifampicin was 90.8% and 91.5%, respectively. The turnaround time for results by MODS was 9 days compared to 21 days by culture on LJ media and an additional 42 days for DST by the 1% proportion method. The cost of performing a single MODS assay was Rs. 250/-, compared to Rs. 950/- for culture and 1st line DST on LJ.

CONCLUSION

MODS was found to be a sensitive and rapid alternative method for performing culture and DST to identify MDR-TB in resource poor settings.

Survival from XDR-TB is associated with modifiable clinical characteristics in rural South Africa

BACKGROUND

Drug-resistant tuberculosis (TB) is a major threat to global public health. Patients with extensively drug-resistant TB (XDR-TB), particularly those with HIV-coinfection, experience high and accelerated mortality with limited available interventions. To determine modifiable factors associated with survival, we evaluated XDR-TB patients from a community-based hospital in rural South Africa where a large number of XDR-TB cases were first detected.

METHODOLOGY/PRINCIPAL FINDINGS

A retrospective case control study was conducted of XDR-TB patients diagnosed from 2005-2008. Survivors, those alive at 180 days from diagnostic sputum collection date, were compared with controls who died within 180 days. Clinical, laboratory and microbiological correlates of survival were assessed in 69 survivors (median survival 565 days [IQR 384-774] and 73 non-survivors (median survival 34 days [IQR 18-90]). Among 129 HIV+ patients, multivariate analyses of modifiable factors demonstrated that negative AFB smear (AOR 8.4, CI 1.84-38.21), a lower laboratory index of routine laboratory findings (AOR 0.48, CI 0.22-1.02), CD4>200 cells/mm(3) (AOR 11.53, 1.1-119.32), and receipt of antiretroviral therapy (AOR 20.9, CI 1.16-376.83) were independently associated with survival from XDR-TB.

CONCLUSIONS/SIGNIFICANCE

Survival from XDR-TB with HIV-coinfection is associated with less advanced stages of both diseases at time of diagnosis, absence of laboratory markers indicative of multiorgan dysfunction, and provision of antiretroviral therapy. Survival can be increased by addressing these modifiable risk factors through policy changes and improved clinical management. Health planners and clinicians should develop programmes focusing on earlier case finding and integration of HIV and drug-resistant TB diagnostic, therapeutic, and preventive activities.

[Drug resistance testing of Mycobacterium tuberculosis isolates from sputum in Chad]

Culture and resistance testing of Mycobacterium tuberculosis are not regularly performed in Chad. Sputa were obtained from three different categories of hospitals (district, regional and national) in Chad. All examined sputa were smear-positive and were investigated by culture and drug resistance testing for first-line antituberculosis drugs. From 232 sputa positive for acid-fast bacilli, 135 isolates of M. tuberculosis from different patients (46 women, 89 men, mean age 34 years) were analyzed. All the patients except one corresponded to new cases of tuberculosis. In total, 27 out of 135 isolates (20%) were resistant to at least one major antituberculosis drug. Resistance to isoniazid was the most frequent resistance observed, with 18 isolates (13%) presenting at least this resistance. Three isolates (2.2%) were resistant to isoniazid and rifampicin (multidrug resistance MDR) including one isolate being concomitantly resistant to streptomycin and ethambutol. The resistance rate differed in relation to the category of the hospital; the most important resistance rate was observed in regional hospitals (33%), while it was 16% and 14% in the national and district hospitals, respectively. HIV serology was performed in 81 patients, among whom 20 (25%) were positive. This is the first study that shows that drug resistance of M. tuberculosis is present in Chad. Besides single drug-resistant isolates, multidrug-resistant strains of M. tuberculosis could also be identified. This result highlights the urgency of initiating actions to detect drug resistance and limit the spread of drug-resistant strains.

Outcomes of multi-drug resistant tuberculosis (MDR-TB) among a cohort of South African patients with high HIV prevalence

BACKGROUND

Multidrug-resistant tuberculosis (MDR-TB) is a major clinical challenge, particularly in patients with human immunodeficiency virus (HIV) co-infection. MDR-TB treatment is increasingly available, but outcomes have not been well characterized. South Africa has provided MDR-TB treatment for a decade, and we evaluated outcomes by HIV status for patients enrolled between 2000 and 2004 prior to anti-retroviral access.

METHODS

We assessed treatment outcomes in a prospective cohort of patients with MDR-TB from eight provincial programs providing second line drugs. World Health Organization definitions were used. Results were stratified by HIV status.

RESULTS

Seven hundred fifty seven patients with known HIV status were included in the final analysis, and HIV infection was documented in 287 (38%). Overall, 348 patients (46.0%) were successfully treated, 74 (9.8%) failed therapy, 177 (23.4%) died and 158 (20.9%) defaulted. Patients with HIV were slightly younger and less likely to be male compared to HIV negative patients. Patients with HIV were less likely to have a successful treatment outcome (40.0 vs. 49.6; P<0.05) and more likely to die (35.2 vs. 16.2; P<0.0001). In a competing risk survival analysis, patients with HIV had a higher hazard of death (HR: 2.33, P<0.0001). Low baseline weight (less than 45 kg and less than 60 kg) was also associated with a higher hazard of death (HR: 2.52, P<0.0001; and HR: 1.50, P<0.0001, respectively, compared to weight greater than 60 kg). Weight less than 45 kg had higher risk of failure (HR: 3.58, P<0.01). Any change in treatment regimen was associated with a higher hazard of default (HR: 2.86; 95% CI 1.55-5.29, P<0.001) and a lower hazard of death (HR: 0.63, P<0.05).

CONCLUSIONS

In this MDR-TB treatment program patients with HIV infection and low weight had higher hazards of death. Overall treatment outcomes were poor. Efforts to improve treatment for MDR-TB are urgently needed.