BackgroundDrug-resistant tuberculosis (DR-TB) remains a threat to global public health, owing to the complexity and delay of diagnosis and treatment. The Global Consortium for Drug-resistant Tuberculosis Diagnostics (GCDD) was formed to develop and evaluate assays designed to rapidly detect DR-TB, so that appropriate treatment might begin more quickly. This paper describes the methodology employed in a prospective cohort study for head-to-head assessment of three different rapid diagnostic tools.MethodsSubjects at risk of DR-TB were enrolled from three countries. Data were gathered from a combination of patient interviews, chart reviews, and laboratory testing from each site’s reference laboratory. The primary outcome of interest was reduction in time from specimen arrival in the laboratory to results of rapid drug susceptibility tests, as compared with current standard mycobacterial growth indicator tube (MGIT) drug susceptibility tests.ResultsSuccessful implementation of the trial in diverse multinational populations is explained, in addition to challenges encountered and recommendations for future studies with similar aims or populations.ConclusionsThe GCDD study was a head-to-head study of multiple rapid diagnostic assays aimed at improving accuracy and precision of diagnostics and reducing overall time to detection of DR-TB. By conducting a large prospective study, which captured epidemiological, clinical, and biological data, we have produced a high-quality unique dataset, which will be beneficial for analyzing study aims as well as answering future DR-TB research questions. Reduction in detection time for XDR-TB would be a major public health success as it would allow for improved treatment and more successful patient outcomes. Executing successful trials is critical in assessment of these reductions in highly variable populations.Trial registrationClinicalTrials.gov NCT02170441.

BackgroundThe aim of this study was to compare the performance of several recently developed assays for the detection of multi- and extensively drug-resistant tuberculosis (M/XDR-TB) in a large, multinational field trial.MethodsSamples from 1,128 M/XDR-TB suspects were examined by Line Probe Assay (LPA), Pyrosequencing (PSQ), and Microscopic Observation of Drug Susceptibility (MODS) and compared to the BACTEC MGIT960 reference standard to detect M/XDR-TB directly from patient sputum samples collected at TB clinics in India, Moldova, and South Africa.ResultsSpecificity for all three assays was excellent: 97–100% for isoniazid (INH), rifampin (RIF), moxifloxacin (MOX) and ofloxacin (OFX) and 99–100% for amikacin (AMK), capreomycin (CAP) and kanamycin (KAN) resistance. Sensitivities were lower, but still very good: 94–100% for INH, RIF, MOX and OFX, and 84–90% for AMK and CAP, but only 48–62% for KAN. In terms of agreement, statistically significant differences were only found for detection of RIF (MODS outperformed PSQ) and KAN (MODS outperformed LPA and PSQ) resistance. Mean time-to-result was 1.1 days for LPA and PSQ, 14.3 days for MODS, and 24.7 days for MGIT.ConclusionsAll three rapid assays evaluated provide clinicians with timely detection of resistance to the drugs tested; with molecular results available one day following laboratory receipt of samples. In particular, the very high specificity seen for detection of drug resistance means that clinicians can use the results of these rapid tests to avoid the use of toxic drugs to which the infecting organism is resistant and develop treatment regiments that have a higher likelihood of yielding a successful outcome.

Funding for this analysis was provided by AltheaDx, which is the manufacturer of the IDgenetix test. AltheaDx personnel assisted in the study design, data collection, and review of the manuscript. Maciel and Garces are employed by AltheaDx. Groessl has received funding as a consultant from American Specialty Health.

Background To develop and evaluate rapid, molecular-based drug susceptibility tests (DST) for extensively drug resistant tuberculosis (XDR-TB), we assembled a phenotypically and genotypically diverse collection of M. tuberculosis (Mtb) isolates from patients evaluated for drug resistance in four high-burden countries. Methods Mtb isolates from India (n=111), Moldova (n=90), the Philippines (n=96), and South Africa (n=103) were selected from existing regional and national repositories to maximize phenotypic diversity for resistance to isoniazid, rifampin, moxifloxacin, ofloxacin, amikacin, kanamycin and capreomycin. MGIT-960 was performed on viable isolates in one laboratory using standardized procedures and drug concentrations. Genetic diversity within drug-resistance phenotypes was assessed. Results Nineteen distinct phenotypes were observed among 400 isolates with complete DST results. Diversity was greatest in the Philippines (14 phenotypes) and least in South Africa (9 phenotypes). Nearly all phenotypes included multiple genotypes. All sites provided isolates resistant to injectable but susceptible to fluoroquinolone drugs. Many patients were taking antibiotics to which their current infection was resistant. Discussion Diverse phenotypes for XDR-TB-defining drugs, including resistance to fluoroquinolone and/or injectable drugs in rifampin-sensitive isolates indicate that rifampin-sensitivity does not ensure effectiveness of a standard four-drug regimen. Thus, rapid, low-cost DST assays for first- and second-line drugs are needed.

BackgroundGrowth-based drug susceptibility testing (DST) is the reference standard for diagnosing drug-resistant tuberculosis (TB), but standard time to result (TTR) is typically ≥ 3 weeks. Rapid tests can reduce that TTR to days or hours, but accuracy may be lowered.In addition to the TTR and test accuracy, the cost of a diagnostic test may affect whether it is adopted in clinical settings. We examine the cost-effectiveness of rapid diagnostics for extremely drug-resistant TB (XDR-TB) in three different high-prevalence settings.Methods1128 patients with confirmed TB were enrolled at clinics in Mumbai, India; Chisinau, Moldova; and Port Elizabeth, South Africa. Patient sputum samples underwent DST for first and second line TB drugs using 2 growth-based (MGIT, MODS) and 2 molecular (Pyrosequencing [PSQ], line-probe assays [LPA]) assays. TTR was the primary measure of effectiveness. Sensitivity and specificity were also evaluated. The cost to perform each test at each site was recorded and included test-specific materials, personnel, and equipment costs. Incremental cost-effectiveness ratios were calculated in terms of $/day saved. Sensitivity analyses examine the impact of batch size, equipment, and personnel costs.ResultsOur prior results indicated that the LPA and PSQ returned results in a little over 1 day. Mean cost per sample without equipment or overhead was $23, $28, $33, and $41 for the MODS, MGIT, PSQ, and LPA, respectively. For diagnosing XDR-TB, MODS was the most accurate, followed by PSQ, and LPA. MODS was quicker and less costly than MGIT. PSQ and LPA were considerably faster but cost more than MODS. Batch size and personnel costs were the main drivers of cost variation.ConclusionsMultiple factors must be weighed when selecting a test for diagnosis of XDR-TB. Rapid tests can greatly improve the time required to diagnose drug-resistant TB, potentially improving treatment success, and preventing the spread of XDR-TB. Faster time to result must be weighed against the potential for reduced accuracy, and increased costs.Trial registrationClinicalTrials.gov Identifier: NCT02170441.Electronic supplementary materialThe online version of this article (10.1186/s12879-018-3013-0) contains supplementary material, which is available to authorized users.