Suitability of Xpert MTB/RIF and Genotype MTBDR
            <i>plus</i>
            for Patient Selection for a Tuberculosis Clinical Trial

Friedrich, Sven O.; Venter, Amour; Kayigire, Xavier A.; Dawson, Rodney; Donald, Peter R.; Diacon, Andreas H.

doi:10.1128/jcm.00138-11

Cited by 37 publications

(47 citation statements)

References 13 publications

(13 reference statements)

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“…There is a large number of studies evaluating Xpert on pulmonary specimens [5,6,[17][18][19][20][21][22][23]; the sensitivity varies from 95% to 100% in smear-positive sputa, and from 47% to 77% in smear-negative ones. Our data score high within these ranges, despite the well-known lower yield of extrapulmonary samples in term of sensitivity.…”

Section: Discussionmentioning

confidence: 99%

Clinical validation of Xpert MTB/RIF for the diagnosis of extrapulmonary tuberculosis

Tortoli¹,

et al. 2012

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Extrapulmonary tuberculosis (EPTB) accounts for more than 20% of tuberculosis (TB) cases. Xpert MTB/RIF (Xpert) (Cepheid, Sunnyvale, CA, USA) is a fully automated amplification system, for which excellent results in the diagnosis of pulmonary TB in highly endemic countries have been recently reported. We aimed to assess the performance of the Xpert system in diagnosing EPTB in a low incidence setting.We investigated with Xpert a large number of consecutive extrapulmonary clinical specimens (1,476, corresponding to 1,068 patients) including both paediatric (494) and adult samples.We found, in comparison with a reference standard consisting of combination of culture and clinical diagnosis of TB, an overall sensitivity and specificity of 81.3% and 99.8% for Xpert, while the sensitivity of microscopy was 48%. For biopsies, urines, pus and cerebrospinal fluids the sensitivity exceeded 85%, while it was slightly under 80% for gastric aspirates. It was, in contrast, lower than 50% for cavitary fluids. High sensitivity and specificity (86.9% and 99.7%, respectively) were also obtained for paediatric specimens.Although the role of culture remains central in the microbiological diagnosis of EPTB, the sensitivity of Xpert in rapidly diagnosing the disease makes it a much better choice compared to smear microscopy. The ability to rule out the disease still remains suboptimal.

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Section: Discussionmentioning

confidence: 99%

Clinical validation of Xpert MTB/RIF for the diagnosis of extrapulmonary tuberculosis

Tortoli¹,

et al. 2012

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“…Several studies have evaluated the performance of the Xpert assay in comparison with those of other molecular assays for either respiratory or nonrespiratory specimens (4)(5)(6)(10)(11)(12). In those studies, the Xpert assay showed performance comparable with that of other molecular assays for respiratory specimens with sensitivities reported between 79 and 93%, while those of other assays ranged from 76 to 96.8%.…”

Section: Discussionmentioning

confidence: 99%

Comparison of the Xpert MTB/RIF and Cobas TaqMan MTB Assays for Detection of Mycobacterium tuberculosis in Respiratory Specimens

et al. 2013

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cThe Xpert MTB/RIF assay (Cepheid, Sunnyvale, CA) is a fully automated, cartridge-based real-time PCR assay designed to detect Mycobacterium tuberculosis and rifampin resistance within 2 h. The performance of the Xpert assay has been evaluated in various clinical settings. However, there are few data comparing the Xpert assay to the Cobas TaqMan MTB test (Roche Diagnostics, Basel, Switzerland), one of the most widely utilized molecular assays for M. tuberculosis detection. In this prospective study, 320 consecutive respiratory specimens were processed simultaneously using acid-fast bacillus (AFB) staining, mycobacterial cultures with both solid and liquid media, and the Cobas and Xpert assays. The Xpert assay was performed with direct respiratory specimens, while the Cobas assay was done with decontaminated concentrated specimens. Based on the culture as a reference method, the overall sensitivities of the Cobas and Xpert assays were 71.4% and 67.9%, respectively. When AFB smear results were taken into consideration, the sensitivities of the Cobas assay for smear-positive and -negative specimens were 87% and 54%, while those of the Xpert assay were 67% and 69%, respectively. The Cobas assay showed 100% specificity and 100% positive predictive value (PPV) regardless of smear results, while the Xpert assay showed 100% specificity and 100% PPV for smear-positive specimens but 98% specificity and 60% PPV for smear-negative specimens. In conclusion, the Xpert assay showed performance that was slightly inferior to that of the Cobas assay but seems useful for the rapid detection of M. tuberculosis, considering that it was performed without laborious and time-consuming decontamination and concentration procedures.

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“…Several recent studies have described the analytic and clinical performance of Xpert MTB/RIF (7)(8)(9)(10)(11)(12)(13)(14)(15).…”

Section: What This Study Adds To the Fieldmentioning

confidence: 99%

“…Several small studies have compared quantitative Xpert MTB/RIF results with more conventional measures of bacterial load, such as direct or concentrated sputum smears, counts of cfu on solid agar growth media, or measures of time-to-detection (TTD) in liquid culture (11,13,14,16). However, these studies have been performed at single sites with limited numbers of samples, which has precluded detailed and generalizable analyses.…”

Section: What This Study Adds To the Fieldmentioning

confidence: 99%

A Multisite Assessment of the Quantitative Capabilities of the Xpert MTB/RIF Assay

Blakemore¹,

Nabeta

Davidow³

et al. 2011

Am J Respir Crit Care Med

105

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Rationale: The Xpert MTB/RIF is an automated molecular test for Mycobacterium tuberculosis that estimates bacterial burden by measuring the threshold-cycle (Ct) of its M. tuberculosis-specific real-time polymerase chain reaction. Bacterial burden is an important biomarker for disease severity, infection control risk, and response to therapy. Objectives: Evaluate bacterial load quantitation by Xpert MTB/RIF compared with conventional quantitative methods. Methods: Xpert MTB/RIF results were compared with smear-microscopy, semiquantiative solid culture, and time-to-detection in liquid culture for 741 patients and 2,008 samples tested in a multisite clinical trial. An internal control real-time polymerase chain reaction was evaluated for its ability to identify inaccurate quantitative Xpert MTB/RIF results. Measurements and Main Results: Assays with an internal control Ct greater than 34 were likely to be inaccurately quantitated; this represented 15% of M. tuberculosis-positive tests. Excluding these, decreasing M. tuberculosis Ct was associated with increasing smear microscopy grade for smears of concentrated sputum pellets (r s ¼ 20.77) and directly from sputum (r s ¼ 20.71). A Ct cutoff of approximately 27.7 best predicted smear-positive status. The association between M. tuberculosis Ct and time-to-detection in liquid culture (r s ¼ 0.68) and semiquantitative colony counts (r s ¼ 20.56) was weaker than smear. Tests of paired same-patient sputum showed that highviscosity sputum samples contained 332 more M. tuberculosis than nonviscous samples. Comparisons between the grade of the acid-fast bacilli smear and Xpert MTB/RIF quantitative data across study sites enabled us to identify a site outlier in microscopy. Conclusions: Xpert MTB/RIF quantitation offers a new, standardized approach to measuring bacterial burden in the sputum of patients with tuberculosis.Keywords: tuberculosis; molecular diagnostics; diagnostic techniques and procedures; diagnosis; clinical trial Measurements of bacterial load have long played an important role in tuberculosis diagnostics. Semiquantitative or quantitative measures of the number of Mycobacterium tuberculosis bacilli present within a clinical sample have been clinically useful for determining disease severity, assessing transmission risk, or monitoring therapy (1-3). Quantitative readouts have also aided in the investigation of potentially false-positive results (4-6).The Xpert MTB/RIF (Cepheid, Sunnyvale, CA) assay simultaneously detects the presence of M. tuberculosis and its susceptibility to the important first-line drug rifampin in less than 2 hours (7). The assay is contained in a small plastic cartridge, and it is run on the GeneXpert platform (Cepheid), a diagnostic The Xpert MTB/RIF assay is a rapid diagnostic test for tuberculosis and rifampin resistance. A number of studies have examined the sensitivity and specificity of the assay in various clinical settings and with various sample types. The test can also provide an estimate of the bacterial load present in the s...

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Suitability of Xpert MTB/RIF and Genotype MTBDR plus for Patient Selection for a Tuberculosis Clinical Trial

Cited by 37 publications

References 13 publications

Clinical validation of Xpert MTB/RIF for the diagnosis of extrapulmonary tuberculosis

Clinical validation of Xpert MTB/RIF for the diagnosis of extrapulmonary tuberculosis

Comparison of the Xpert MTB/RIF and Cobas TaqMan MTB Assays for Detection of Mycobacterium tuberculosis in Respiratory Specimens

A Multisite Assessment of the Quantitative Capabilities of the Xpert MTB/RIF Assay

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