Tuberculosis in the developing world: recent advances in diagnosis with special consideration of extensively drug-resistant tuberculosis

Molecular Characterization of Mutations in Isoniazid- and Rifampicin-Resistant Mycobacterium tuberculosis Isolated in Thailand

The control of drug-resistant tuberculosis (TB) is a major challenge. The frequency and mutation characteristics indicate the efficiency of molecular tests for the rapid detection of TB drug resistance. This study examined the existence of katG and inhA mutations for isoniazid (INH) resistance and rpoB mutations for rifampicin (RFP) resistance. In total, 178 drug-resistant Mycobacterium tuberculosis (MTB) isolates were analyzed. Mutations in katG encoding and inhA regulatory regions were detected in 136/168 (81.0%) and 29/168 (17.3%), respectively, with the most prominent mutation of Ser315Thr substitution in katG in 126/168 (75.0%), and -15 C to T substitution in the regulatory region of the inhA (26/168; 15.5%). Two distinct katG mutations (Tyr337Cys, 1003InsG) were identified. Of 125 RFP-resistant isolates, 118 (94.4%) carried mutations affecting the 81-bp RFP resistance-determining region, with the most commonly affected codons 450, 445, and 435 identified in 74 (59.2%), 26 (20.8%), and 12 (9.6%) isolates, respectively. Genetic mutations were highly associated with phenotypic INH and RFP resistance, and the majority shared similarities with those reported in previous studies in Thailand and other Asian countries. These data are useful for guiding the use and improvement of molecular tests for TB drug resistance.

A university-clustered tuberculosis outbreak during the COVID-19 pandemic in eastern China

During the COVID-19 pandemic in 2020, a tuberculosis outbreak occurred in a university in eastern China, with 4,488 students and 421 staff on the campus. A 19-year-old student was diagnosed in August 2019. Later, the first round of screening was initiated among close contacts, but no active cases were found. Till September 2020, four rounds of screening were performed. Four rounds of screening were conducted on September 9, November 8, November 22-25 in 2019 and September 2020, with 0, 5, 0 and 43 cases identified, respectively. A total of 66 active tuberculosis were found in the same university, including 4 sputum culture-positive and 7 sputum smear-positive. The total attack rate of active tuberculosis was 1.34% (66/4909). The whole-genome sequencing showed that the isolates belonged to the same L2 sub-specie and were sensitive to all tested antituberculosis drugs. Delay detection, diagnosis and report of cases were the major cause of this university tuberculosis epidemic. More attention should be paid to the asymptomatic students in the index class. After the occurrence of tuberculosis cases in schools, multiple rounds of screening should be carried out, and preventive therapy should be applied in a timely manner.

Developments in the Diagnostic Techniques of Infectious Diseases: Rural and Urban Prospective

Objectives:

Diagnostics is the first step for the treatment and eradication of infectious microbial diseases. Due to ever evolving pathogens and emerging new diseases, there is an urgent need to identify suitable diagnostic techniques for better management of each disease. The success rate of specific diagnostic technique in any population depends on various factors including type of the microbial pathogen, availability of resources, technical expertise, disease severity and degree of epidemic of disease in the area. One of the important tasks of the policy makers is to identify and implement suitable diagnostic techniques for specific regions based on their specific requirements. In this review we have discussed various techniques available in the literature and their suitability for the target population based on above mentioned criteria.

Methods:

Diagnostic techniques evaluation of well documented representative microbial diseases; Tuberculosis (bacterial), Malaria (parasitic) and HIV (viral) were included in the study. Identification and collection of information and data was performed focusing on the diagnostic techniques used from the scientific publications from Pubmed, Science Access, Scopus, EMBASE and several regional databases. WHO and CDC database for Tuberculosis, Malaria and HIV were also included. These techniques were compared with respect to the financial resource availability, expertise and management, functional capacity, pathogen virulence and degree of epidemic in the population.

Results and Conclusion:

In case of Tuberculosis, ELISA and colorimetric techniques are successful in rural and urban communities with 80% – 90% sensitivity. Genotyping and SNP analysis are useful in drug resistant strains. Parasitic disease Malaria also follows the same trend with diagnostic techniques like RDTs being common in both population with fast results and around 90% sensitivity. STD disease like HIV however shows slight different trends due to urgent need of interference in rural epidemics of the disease. Rapid and sensitive immunotechniques like dipsticks and agglutination with almost 100% sensitivity are used in both rural and urban areas. For the confirmation further tests are done like protein Western and NAAT. Advance techniques could be the option for higher epidemic area, drug resistance and disease research, while rapid techniques would be suitable for low income areas and POC facilities. Therefore, suitability of the diagnostic techniques for better management depends not only on the financial resources and assessment skills of a community but sometimes on the disease itself. We have further discussed the technological improvements for specific settings (rural/urban) based on the past research for better management of diseases, which could be implemented for the understanding of understudied and newly emerging diseases.

Molecular detection of rifampicin resistance by GeneXpert® assay among treated and untreated pulmonary tuberculosis patients from Khyber Pakhtunkhwa, Pakistan

OBJECTIVES

Drug-resistant tuberculosis (TB) is an emerging health problem. Rifampicin (RIF) is the major first-line drug against TB. RIF resistance can be used as a marker for the detection of multidrug-resistant TB (MDR-TB). The purpose of this study was to determine the RIF resistance pattern of Mycobacterium tuberculosis complex isolates among treated and untreated patients in Khyber Pakhtunkhwa, Pakistan.

METHODS

A total of 349 drug-treated and untreated TB-diagnosed patients were enrolled in this study. RIF resistance was detected using a GeneXpert^® assay for amplification of the RIF resistance-determining region (RRDR) region of the rpoB gene.

RESULTS

The overall prevalence of RIF resistance was 5.2% (18/349). Among 49 untreated TB patients, 3 samples (6.1%) were found resistant to RIF. Among 235 patients with a category 1 treatment regimen, 10 samples (4.3%) were resistant to RIF, whilst among 65 patients with a category 2 (Cat-2) treatment regimen, 5 samples (7.7%) were resistant to RIF. A comparison based on patient sex revealed high RIF resistance among male compared with female patients. RIF resistance was highest (4/21; 19.0%) in the 21-40 years age group among Cat-2 patients.

CONCLUSIONS

The overall prevalence of RIF resistance was high among treated and untreated TB patients. These findings will be helpful for better monitoring and management of RIF resistance in TB patients from Khyber Pakhtunkhwa, Pakistan.

Effect of efflux pump inhibitors on the susceptibility of Mycobacterium tuberculosis to isoniazid

BACKGROUND

Mycobacterium can develop drug resistance (DR) by mutation of its existing gene. However, the existence of DR without mutation shows the need to look for an alternative mechanism such as the role of efflux pumps. In this study, we examined the effect of efflux pump inhibitors on isoniazid (INH) susceptibility in clinical isolates of Mycobacterium tuberculosis (Mtb).

MATERIALS AND METHODS

Resazurin microtiter assay was used to examine the effect of efflux pump inhibitors on minimum inhibitory concentration (MIC) levels of INH in eighteen Mtb clinical isolates.

RESULTS

The observed reduction in INH-MIC was 2-16-fold in INH-resistant isolates with katG and inhA gene mutations, 2-8-fold in INH-resistant isolates without mutation and 2-4-fold in INH-sensitive isolates. The MIC reduction by verapamil (VER) was observed in 83% isolates, by carbonyl cyanide m-chlorophenylhydrazone (CCCP) 61% isolates, by chloropromazine (CPZ) 61% isolates, by reserpine (RES) in 61% isolates and by 2,4-dinitro phenol (DNP) in 55% isolates.

INTERPRETATION AND CONCLUSIONS

The results obtained in this study confirm that MIC of INH decreased in the presence of efflux pump inhibitors (VER, CCCP, CPZ, DNP, RES) in clinical isolates of Mtb and that the inhibition of efflux pumps by the efflux pump inhibitors can enhance the clinical effect of a drug. The results showed that these efflux pump inhibitors are active against both drug susceptible and drug resistant isolates, indicating that the effect of efflux pump inhibitors is not dependent on the mutational profile of the isolate. We observed in this study that VER was the most effective efflux pump inhibitor.

Risk factors for extensively drug-resistant tuberculosis: a review

INTRODUCTION

Extensively drug-resistant tuberculosis (XDR-TB) is emerging as a global public health problem. Its treatment is more expensive and difficult, and the outcomes much severe. The identification of risk factors for XDR-TB is of paramount importance to design effective TB control strategies.

OBJECTIVE

To review published articles on risk factors for XDR-TB.

METHODS

We identified 249 English articles on PubMed, and 182 were excluded by the abstract. The remaining articles were retrieved for full-text detailed evaluation by authors, and 27 relevant articles were selected for final review.

RESULTS

Some risk factors were consistently present, mainly previous TB treatment and its length. Other conditions often associated were immigration, alcoholism and HIV coinfection. Pre-XDR-TB points to an increased risk of XDR-TB.

CONCLUSION

The information regarding determinants of XDR-TB is relatively weak. However, special emphasis should be given to minimize the risks of TB retreatment to prevent the emergence of highly resistant TB.

A systematic review of rapid drug susceptibility tests for multidrug-resistant tuberculosis using rifampin resistance as a surrogate

BACKGROUND

The emergence of multidrug-resistant tuberculosis (MDR-TB) has prompted the development of rapid drug susceptibility assays with a focus on rifampin in recent years. Systematic reviews with evaluation of predictive values for different assays are scarce.

METHOD

MEDLINE was searched on 6 September 2008 for English articles that contain concurrent original data for generating summary measures of sensitivity, specificity and likelihood ratios of rapid rifampin susceptibility assays.

RESULTS/CONCLUSIONS

Significant heterogeneity was found in likelihood ratios across studies of all assays except nitrate reductase assay and colorimetric assays. Although rapid assays are fairly reliable for ruling out MDR-TB, careful consideration of clinical risk factors is required before using these assays to rule in MDR-TB under different epidemiological settings.

The impact of expanded testing for multidrug resistant tuberculosis using genotype [correction of geontype] MTBDRplus in South Africa: an observational cohort study

INTRODUCTION

Globally, multidrug resistant tuberculosis (MDR-TB) remains underdiagnosed. The Genotype MTBDRplus®, a rapid drug susceptibility testing (DST) assay used to detect resistance to isoniazid and rifampicin in the diagnosis of MDR-TB, has good diagnostic accuracy, but its impact on patient outcomes in routine practice is unproven. We assessed the clinical impact of routine DST using MTBDRplus in a single health district in South Africa.

METHODS

Data were collected on all adult pulmonary TB patients registered at 25 public health clinics in the periods before and after introduction of an expanded DST algorithm using MTBDRplus version 1.0.

RESULTS

We collected data on 1176 TB patients before implementation and 1177 patients afterwards. In the before period, measured MDR-TB prevalence among new cases was 0.7% (95% CI1.4-3.1%), and among retreatment cases 6.2% (95% CI:3.5-8.8%), versus 3.7% (95% CI:2.4-5.0, p<0.01) and 6.6% (95% CI:3.8-9.4%, p = 0.83) respectively after MTBDRplus introduction. The median times from sputum collection to MDR treatment in the before and after periods were 78 days (IQR:52-93) and 62 days (IQR:32-86, p = 0.05), respectively. Among MDR-TB cases, 27% (95%CI:10-44) in the before period converted sputum cultures to negative by 8 months following treatment initiation, while 52% (95%CI:38-66) converted in the intervention period (p = 0.04).

CONCLUSIONS

The expanded use of MTBDRplus DST resulted in a substantial increase in the proportion of new cases identified as MDR-TB; though time to MDR treatment was reduced, it was still over two months. Culture conversion for MDR-TB patients improved after introduction of MTBDRplus. This work illustrates the mixture of successes and challenges resulting from increased access to rapid DST in a setting with a high TB burden.

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.

Current tuberculosis diagnostic tools & role of urease breath test

Tuberculosis (TB) remains a significant public health issue worldwide especially in developing countries, where the disease is endemic, and effective TB diagnostic as well as treatment-monitoring tools are serious barriers to defeating the disease. Detection of pathogen-specific metabolic pathways offers a potential alternative to current methods, which focus on bacterial growth, bacterial nucleic acid amplification, or detection of host immune response to the pathogen. Metabolic pathway detection may provide rapid and effective new tools for TB that can improve TB diagnostics for children and HIV infected patients. Metabolic breath tests are attractive because these are safe, and provide an opportunity for rapid point of care diagnostics and tool for drug efficacy evaluation during clinical trials. Our group has developed a rabbit urease breath test model to evaluate the sensitivity and the specificity of urease based detection of Mycobacterium tuberculosis. TB infected rabbits were given stable isotopically labelled urea as the substrate. The urea tracer was metabolized to 13 C-CO 2 and detected in exhaled breaths using portable infrared spectrometers. The signal correlated with bacterial load both for primary diagnostics and treatment monitoring. Clinical trials are currently ongoing to evaluate the value of the test in clinical management settings. Urea breath testing may provide a useful diagnostic and biomarker assay for tuberculosis and treatment response.

Analysis of gene mutations associated with isoniazid, rifampicin and ethambutol resistance among Mycobacterium tuberculosis isolates from Ethiopia

Background

The emergence of drug resistance is one of the most important threats to tuberculosis control programs. This study was aimed to analyze the frequency of gene mutations associated with resistance to isoniazid (INH), rifampicin (RMP) and ethambutol (EMB) among Mycobacterium tuberculosis isolates from Northwest Ethiopia, and to assess the performance of the GenoType^® MTBDRplus and GenoType^® MTBDRsl assays as compared to the BacT/ALERT 3D system.

Methods

Two hundred sixty Mycobacterium tuberculosis isolates from smear positive tuberculosis patients diagnosed between March 2009 and July 2009 were included in this study. Drug susceptibility tests were performed in the Institute of Medical Microbiology and Epidemiology of Infectious Diseases, University Hospital of Leipzig, Germany.

Results

Of 260 isolates, mutations conferring resistance to INH, RMP, or EMB were detected in 35, 15, and 8 isolates, respectively, while multidrug resistance (MDR) was present in 13 of the isolates. Of 35 INH resistant strains, 33 had mutations in the katG gene at Ser315Thr 1 and two strains had mutation in the inhA gene at C15T. Among 15 RMP resistant isolates, 11 had rpoB gene mutation at Ser531Leu, one at His526Asp, and three strains had mutations only at the wild type probes. Of 8 EMB resistant strains, two had mutations in the embB gene at Met306Ile, one at Met306Val, and five strains had mutations only at the wild type probes. The GenoType^® MTBDRplus assay had a sensitivity of 92% and specificity of 99% for INH resistance, and 100% sensitivity and specificity to detect RMP resistance and MDR. The GenoType^® MTBDRsl assay had a sensitivity of 42% and specificity of 100% for EMB resistance.

Conclusion

The dominance of single gene mutations associated with the resistance to INH and RMP was observed in the codon 315 of the katG gene and codon 531 of the rpoB gene, respectively. The GenoType^® MTBDRplus assay is a sensitive and specific tool for diagnosis of resistance to INH, RMP and MDR. However, the GenoType^® MTBDRsl assay shows limitations in detecting resistance to EMB.

Evaluation of tuberculosis diagnostics: establishing an evidence base around the public health impact

The limitations of existing tuberculosis diagnostic tools are significantly hampering tuberculosis control efforts, most noticeably in areas with high prevalence of human immunodeficiency virus (HIV) infection and antituberculosis drug resistance. However, renewed global interest in tuberculosis research has begun to bear fruit, with several new diagnostic technologies progressing through the development pipeline. There are significant challenges in building a sound evidence base to inform public health policies because most diagnostic research focuses on the accuracy of individual tests, with often significant limitations in the design, conduct, and reporting of diagnostic accuracy studies. Diagnostic accuracy studies may not be appropriate to guide public health policies, and clinical trials may increasingly be required to determine the incremental value and cost-effectiveness of new tools. The urgent need for new diagnostics should not distract from pursuing rigorous scientific evaluation focused on public health impact.

Analytical performance of the Roche LightCycler® Mycobacterium Detection Kit for the diagnosis of clinically important mycobacterial species

BACKGROUND

The LightCycler® Mycobacterium Detection Kit based on real-time PCR technology for the detection of Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium kansasii was recently developed. This study evaluated its analytical sensitivity, specificity and reproducibility.

METHODOLOGY/PRINCIPAL FINDINGS

Plasmid standards were prepared and used to determine the limit of detection. The assay was also performed against organisms other than mycobacteria, other mycobacterial strains and interfering substances to exclude cross-reactivity and interference. Reference standards were prepared and tested to assess the assay's reproducibility. All PCR assays were performed using the LightCycler® 2.0 Instrument. The detection limit for M. tuberculosis was 28 copies per microlitre. Neither cross-reactivity nor interference occurred with non-mycobacterial organisms and substances tested. Overall reproducibility for consecutive measurements, run-to-run, lot-to-lot, day-to-day and laboratory-to-laboratory achieved a coefficient of variance of less than two percent.

SIGNIFICANCE

The LightCycler® Mycobacterium Detection kit has shown to be a robust and accurate assay with the potential to be used as a rapid TB diagnostic test.

Is there a role for fluorine 18 fluorodeoxyglucose-positron emission tomography and positron emission tomography/computed tomography in evaluating patients with mycobacteriosis? A systematic review

OBJECTIVE

This study was designed to review the emerging role of fluorine 18 fluorodeoxyglucose (¹⁸F-FDG)-positron emission tomography (PET) CT/computed tomography (PET/CT) in patients with mycobacteriosis.

METHODS

A comprehensive literature search of published studies through October 2010 in PubMed/MEDLINE database regarding ¹⁸F-FDG-PET and PET/CT in patients with mycobacteriosis was performed.

RESULTS

Ultimately, we identified 16 studies comprising a total of 220 patients with mycobacteriosis. Main findings of the included studies are presented.

CONCLUSIONS

(1) Mycobacteriosis commonly causes increased ¹⁸F-FDG uptake; therefore, positive ¹⁸F-FDG-PET results should be interpreted with caution in differentiating benign from malignant abnormalities. (2) ¹⁸F-FDG-PET and PET/CT are potentially useful in detecting sites of Mycobacterium infection. (3) Dual-phase ¹⁸F-FDG-PET is not useful for the differential diagnosis between malignant lesions and sites of Mycobacterium infection. (4) ¹⁸F-FDG-PET and PET/CT are useful for the evaluation of disease activity and in monitoring response to therapy in patients with mycobacteriosis. (5) Dual-tracer PET and PET/CT are potentially useful for presumptive diagnosis of solitary pulmonary nodules.

Application of genotype MTBDRplus in rapid detection of the Mycobacterium tuberculosis complex as well as its resistance to isoniazid and rifampin in a high volume laboratory in Southern China

The alarmingly worsening epidemics of drug-resistant tuberculosis (TB) call urgent need for a simple method for the rapid detection of drug-resistant TB in clinical settings. In an attempt to establish a rapid procedure for laboratory diagnosis of TB and investigate the local TB epidemiology, molecular line probe assay of the Genotype MTBDRplus was used to identify Mycobacterium tuberculosis complex (MTBC) and detect mutations conferring resistance to two most active first-line drugs against TB: Rifampin and Isoniazid. 96 acid-fast bacillus (AFB) smear- positive sputums and 18 PCR-positive non-sputum specimens have been determined for the MTBC and resistance to Rifampin and Isoniazid. The MTBC detection rates in two sources of specimens were 93.8% (90/96) and 77.8% (14/18) respectively. The overall drug resistance (Rifampin or Isoniazid) occurred in 34.6% (36/104). Resistance to rifampin (RMP) was 28.8% (30/104) and 25% (26/104) was to Isoniazid (INH), in which high level drug resistance accounted for 88.5% (23/26) and low level drug resistance accounted for 7.7% (2/26). Multidrug resistance (MDR), defined as resistant to both RMP and INH, was found in 19.2% (20/104) of clinical samples, which was double that of official statistics. In addition, 63.3% (19/30) RMP-resistant mutations were identified in the region of RopB 530-533 and 57.9% (11/19) were the S531L mutation. 84.6% (22/26) of resistance to INH was mediated by Kat S315T1 mutations which conferred the high-level resistance to INH. The Genotype MTBDRplus line probe assay is a suitable and applicable method for establishing the rapidness in detection of drug-resistant TB in clinical laboratory. It will be a valuable addition to the conventional TB diagnostic approaches.

13[C]-urea breath test as a novel point-of-care biomarker for tuberculosis treatment and diagnosis

Background

Pathogen-specific metabolic pathways may be detected by breath tests based on introduction of stable isotopically-labeled substrates and detection of labeled products in exhaled breath using portable infrared spectrometers.

Methodology/Principal Findings

We tested whether mycobacterial urease activity could be utilized in such a breath test format as the basis of a novel biomarker and diagnostic for pulmonary TB. Sensitized New-Zealand White Rabbits underwent bronchoscopic infection with either Mycobacterium bovis or Mycobacterium tuberculosis. Rabbits were treated with 25 mg/kg of isoniazid (INH) approximately 2 months after infection when significant cavitary lung pathology was present. [¹³C] urea was instilled directly into the lungs of intubated rabbits at selected time points, exhaled air samples analyzed, and the kinetics of δ¹³CO₂ formation were determined. Samples obtained prior to inoculation served as control samples for background ¹³CO₂ conversion in the rabbit model. ¹³CO₂, from metabolic conversion of [¹³C]-urea by mycobacterial urease activity, was readily detectable in the exhaled breath of infected rabbits within 15 minutes of administration. Analyses showed a rapid increase in the rate of ¹³CO₂ formation both early in disease and prior to treatment with INH. Following INH treatment, all evaluable rabbits showed a decrease in the rate of ¹³CO₂ formation.

Conclusions/Significance

Urea breath testing may provide a useful diagnostic and biomarker assay for tuberculosis and for treatment response. Future work will test specificity for M. tuberculosis using lung-targeted dry powder inhalation formulations, combined with co-administering oral urease inhibitors together with a saturating oral dose of unlabeled urea, which would prevent the δ¹³CO₂ signal from urease-positive gastrointestinal organisms.

Tuberculosis as part of the natural history of HIV infection in developing countries

An enhanced, refocused research agenda is critical to reducing the burden of tuberculosis (TB) in the human immunodeficiency virus (HIV) epidemic in developing countries. TB threatens HIV-infected patients before and after initiation of antiretroviral therapy, is difficult to diagnose, is rapidly fatal when it is drug resistant, and is being spread in clinics and hospitals. Research priorities include improved and point-of-care TB diagnostics; TB treatment and prevention during HIV infection, drug-resistant TB, and childhood TB; and optimization of TB and HIV program integration. With new TB diagnostics and drugs reaching approval, research must focus on effectively deploying these advancements. Research must include evaluations of individual, household, health care, and community approaches. Studies must apply implementation science to determine how to increase and adapt effective interventions to reduce TB burden in the context of HIV infection. Investment in this research will improve the lives of persons infected with HIV and contribute to efforts to reduce the global TB burden.

Multidrug-resistant and extensively drug-resistant tuberculosis: a threat to global control of tuberculosis

Although progress has been made to reduce global incidence of drug-susceptible tuberculosis, the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis during the past decade threatens to undermine these advances. However, countries are responding far too slowly. Of the estimated 440,000 cases of MDR tuberculosis that occurred in 2008, only 7% were identified and reported to WHO. Of these cases, only a fifth were treated according to WHO standards. Although treatment of MDR and XDR tuberculosis is possible with currently available diagnostic techniques and drugs, the treatment course is substantially more costly and laborious than for drug-susceptible tuberculosis, with higher rates of treatment failure and mortality. Nonetheless, a few countries provide examples of how existing technologies can be used to reverse the epidemic of MDR tuberculosis within a decade. Major improvements in laboratory capacity, infection control, performance of tuberculosis control programmes, and treatment regimens for both drug-susceptible and drug-resistant disease will be needed, together with a massive scale-up in diagnosis and treatment of MDR and XDR tuberculosis to prevent drug-resistant strains from becoming the dominant form of tuberculosis. New diagnostic tests and drugs are likely to become available during the next few years and should accelerate control of MDR and XDR tuberculosis. Equally important, especially in the highest-burden countries of India, China, and Russia, will be a commitment to tuberculosis control including improvements in national policies and health systems that remove financial barriers to treatment, encourage rational drug use, and create the infrastructure necessary to manage MDR tuberculosis on a national scale.

Diagnostic accuracy of the microscopic observation drug susceptibility assay: a pilot study from India

SETTING

The microscopic observation drug susceptibility (MODS) assay is a rapid, sensitive, low-cost liquid culture technique.

OBJECTIVE

To establish the accuracy of MODS for the detection of active pulmonary tuberculosis (TB), and to document the costs and challenges of setting up this assay in a low-income setting.

DESIGN

Prospective blinded pilot study of 200 adult TB suspects at a tertiary referral hospital in India. Reference standard included culture (Löwenstein-Jensen and automated liquid culture) and clinical diagnosis.

RESULTS

Patients were mostly male (n = 122, 61.1%) and out-patients (n = 184, 92.0%), with a mean age of 40.4 years (standard deviation 16.2). Seventeen (8.5%) were human immunodeficiency virus infected and 47 (23.5%) were reference culture-positive. Compared to reference culture, MODS was 78.9% sensitive (95%CI 62.2-90.0) and 96.7% specific (95%CI 92.0-98.8). Clinical assessment suggested that MODS was false-negative in 3/8 reference culture-positive MODS-negatives and true-positive in 4/6 reference culture-negative MODS-positives. MODS was faster than solid (P < 0.001) and liquid culture (P = 0.088), and cheaper than both.

CONCLUSION

MODS may be a good alternative to automated liquid culture, but there were several challenges in setting up the assay. Prior training and validation, setup costs and inability to rule out cross-contamination need to be taken into account before the test can be established.

Polymorphisms associated with resistance and cross-resistance to aminoglycosides and capreomycin in Mycobacterium tuberculosis isolates from South Korean Patients with drug-resistant tuberculosis

The aminoglycosides streptomycin, amikacin, and kanamycin and the cyclic polypeptide capreomycin are all widely used in second-line therapy for patients who develop multidrug-resistant tuberculosis. We have characterized a set of 106 clinical isolates of Mycobacterium tuberculosis using phenotypic drug susceptibility testing (DST) to determine the extent of resistance to each agent and cross-resistance between agents. These results were compared with polymorphisms in the DNA sequences of ribosome-associated genes previously implicated in resistance and with the clinical outcomes of subjects from whom these isolates were obtained. Thirty-six (34%) of these isolates displayed resistance to one or more of these agents, and the majority of these (20 of 36) showed cross-resistance to one or more agents. Most (33 of 36) of the resistant isolates showed polymorphisms in the 16S ribosome components RpsL and rrs. Three resistant strains (3 of 36) were identified that had no known polymorphisms in ribosomal constituents. For kanamycin and streptomycin, molecular DST significantly outperformed phenotypic DST using the absolute concentration method for predicting 4-month sputum conversion (likelihood ratios of 4.0 and 2.0, respectively) and was equivalent to phenotypic DST using the National Committee for Clinical Laboratory Standards (NCCLS)-approved agar proportion method for estimating MIC (likelihood ratio, 4.0). These results offer insight into mechanisms of resistance and cross-resistance among these agents and suggest that the development of rapid molecular tests to distinguish polymorphisms would significantly enhance clinical utility of this important class of second-line antituberculosis drugs.