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Direct nitrate reductase assay versus microscopic observation drug susceptibility test for rapid detection of MDR-TB in Uganda.

ABSTRACT: The most common method for detection of drug resistant (DR) TB in resource-limited settings (RLSs) is indirect susceptibility testing on Lowenstein-Jensen medium (LJ) which is very time consuming with results available only after 2-3 months. Effective therapy of DR TB is therefore markedly delayed and patients can transmit resistant strains. Rapid and accurate tests suitable for RLSs in the diagnosis of DR TB are thus highly needed. In this study we compared two direct techniques--Nitrate Reductase Assay (NRA) and Microscopic Observation Drug Susceptibility (MODS) for rapid detection of MDR-TB in a high burden RLS. The sensitivity, specificity, and proportion of interpretable results were studied. Smear positive sputum was collected from 245 consecutive re-treatment TB patients attending a TB clinic in Kampala, Uganda. Samples were processed at the national reference laboratory and tested for susceptibility to rifampicin and isoniazid with direct NRA, direct MODS and the indirect LJ proportion method as reference. A total of 229 specimens were confirmed as M. tuberculosis, of these interpretable results were obtained in 217 (95%) with either the NRA or MODS. Sensitivity, specificity and kappa agreement for MDR-TB diagnosis was 97%, 98% and 0.93 with the NRA; and 87%, 95% and 0.78 with the MODS, respectively. The median time to results was 10, 7 and 64 days with NRA, MODS and the reference technique, respectively. The cost of laboratory supplies per sample was low, around 5 USD, for the rapid tests. The direct NRA and MODS offered rapid detection of resistance almost eight weeks earlier than with the reference method. In the study settings, the direct NRA was highly sensitive and specific. We consider it to have a strong potential for timely detection of MDR-TB in RLS.

SUBMITTER: Bwanga F

PROVIDER: S-EPMC3090408 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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Direct nitrate reductase assay versus microscopic observation drug susceptibility test for rapid detection of MDR-TB in Uganda.

Bwanga Freddie F Haile Melle M Joloba Moses L ML Ochom Emmanuel E Hoffner Sven S

PloS one 20110509 5

The most common method for detection of drug resistant (DR) TB in resource-limited settings (RLSs) is indirect susceptibility testing on Lowenstein-Jensen medium (LJ) which is very time consuming with results available only after 2-3 months. Effective therapy of DR TB is therefore markedly delayed and patients can transmit resistant strains. Rapid and accurate tests suitable for RLSs in the diagnosis of DR TB are thus highly needed. In this study we compared two direct techniques--Nitrate Reduct ...[more]

PMID: 21573015

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Project description:New diagnostic tools are urgently needed to interrupt the transmission of tuberculosis and multidrug-resistant tuberculosis. Rapid, sensitive detection of tuberculosis and multidrug-resistant tuberculosis in sputum has been demonstrated in proof-of-principle studies of the microscopic-observation drug-susceptibility (MODS) assay, in which broth cultures are examined microscopically to detect characteristic growth.In an operational setting in Peru, we investigated the performance of the MODS assay for culture and drug-susceptibility testing in three target groups: unselected patients with suspected tuberculosis, prescreened patients at high risk for tuberculosis or multidrug-resistant tuberculosis, and unselected hospitalized patients infected with the human immunodeficiency virus. We compared the MODS assay head-to-head with two reference methods: automated mycobacterial culture and culture on Löwenstein-Jensen medium with the proportion method.Of 3760 sputum samples, 401 (10.7%) yielded cultures positive for Mycobacterium tuberculosis. Sensitivity of detection was 97.8% for MODS culture, 89.0% for automated mycobacterial culture, and 84.0% for Löwenstein-Jensen culture (P<0.001); the median time to culture positivity was 7 days, 13 days, and 26 days, respectively (P<0.001), and the median time to the results of susceptibility tests was 7 days, 22 days, and 68 days, respectively. The incremental benefit of a second MODS culture was minimal, particularly in patients at high risk for tuberculosis or multidrug-resistant tuberculosis. Agreement between MODS and the reference standard for susceptibility was 100% for rifampin, 97% for isoniazid, 99% for rifampin and isoniazid (combined results for multidrug resistance), 95% for ethambutol, and 92% for streptomycin (kappa values, 1.0, 0.89, 0.93, 0.71, and 0.72, respectively).A single MODS culture of a sputum sample offers more rapid and sensitive detection of tuberculosis and multidrug-resistant tuberculosis than the existing gold-standard methods used.

Project description:BackgroundThe Union in collaboration with national TB programme (NTP) started the community-based MDR-TB care (CBMDR-TBC) project in 33 townships of upper Myanmar to improve treatment initiation and treatment adherence. Patients with MDR-TB diagnosed/registered under NTP received support through the project staff, in addition to the routine domiciliary care provided by NTP staff. Each township had a project nurse exclusively for MDR-TB and 30 USD per month (max. for 4 months) were provided to the patient as a pre-treatment support.ObjectivesTo assess whether CBMDR-TBC project's support improved treatment initiation.MethodsIn this cohort study (involving record review) of all diagnosed MDR-TB between January 2015 and June 2016 in project townships, CBMDR-TBC status was categorized as "receiving support" if date of project initiation in patient's township was before the date of diagnosis and "not receiving support", if otherwise. Cox proportional hazards regression (censored on 31 Dec 2016) was done to identify predictors of treatment initiation.ResultsOf 456 patients, 57% initiated treatment: 64% and 56% among patients "receiving support (n = 208)" and "not receiving support (n = 228)" respectively (CBMDR-TBC status was not known in 20 (4%) patients due to missing diagnosis dates). Among those initiated on treatment (n = 261), median (IQR) time to initiate treatment was 38 (20, 76) days: 31 (18, 50) among patients "receiving support" and 50 (26,101) among patients "not receiving support". After adjusting other potential confounders (age, sex, region, HIV, past history of TB treatment), patients "receiving support" had 80% higher chance of initiating treatment [aHR (0.95 CI): 1.8 (1.3, 2.3)] when compared to patients "not receiving support". In addition, age 15-54 years, previous history of TB and being HIV negative were independent predictors of treatment initiation.ConclusionReceiving support under CBMDR-TBC project improved treatment initiation: it not only improved the proportion initiated but also reduced time to treatment initiation. We also recommend improved tracking of all diagnosed patients as early as possible.

Project description:BackgroundMixed M. tuberculosis (MTB) infection occurs when one is infected with more than one clonally distinct MTB strain. This form of infection can assist MTB strains to acquire additional mutations, facilitate the spread of drug-resistant strains, and boost the rate of treatment failure. Hence, the presence of mixed MTB infection could affect the performance of some rapid molecular diagnostic tests such as Line Probe Assay (LPA) and GeneXpert MTB/RIF (Xpert) assays.MethodsThis was a cross-sectional study that used sputum specimens collected from participants screened for STREAM 2 clinical trial between October 2017 and October 2019. Samples from 62 MTB smear-positive patients and rifampicin-resistant patients from peripheral health facilities were processed for Xpert and LPA as screening tests for eligibility in the trial. From November 2020, processed stored sputum samples were retrieved and genotyped to determine the presence of mixed-MTB strain infection using a standard 24-locus Mycobacterial Interspersed Repetitive Unit-Variable Number Tandem-Repeat (MIRU-VNTR). Samples with at least 20/24 MIRU-VNTR loci amplified were considered for analysis. Agar proportional Drug Susceptibility Test (DST) was performed on culture isolates of samples that had discordant results between LPA and Xpert. The impact of the presence of mixed-MTB strain on Xpert and LPA test interpretation was analyzed.ResultsA total of 53/62 (85%) samples had analyzable results from MIRU-VNTR. The overall prevalence of mixed-MTB infection was 5/53 (9.4%). The prevalence was highest among male's 3/31 (9.7%) and among middle-aged adults, 4/30 (33.3%). Lineage 4 of MTB contributed 3/5 (60.0%) of the mixed-MTB infection prevalence. Having mixed MTB strain infection increased the odds of false susceptible Xpert test results (OR 7.556, 95% CI 0.88-64.44) but not for LPA. Being HIV-positive (P = 0.04) independently predicted the presence of mixed MTB infection.ConclusionsThe presence of mixed-MTB strain infection may affect the performance of the GeneXpert test but not for LPA. For patients with high pre-test probability of rifampicin resistance, an alternative rapid method such as LPA should be considered.

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Direct nitrate reductase assay versus microscopic observation drug susceptibility test for rapid detection of MDR-TB in Uganda.

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Direct nitrate reductase assay versus microscopic observation drug susceptibility test for rapid detection of MDR-TB in Uganda.

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