A multisite assessment of the quantitative capabilities of the Xpert MTB/RIF assay

Robert Blakemore, Pamela Nabeta, Amy L. Davidow, Viral Vadwai, Rasim Tahirli, Vanisha Munsamy, Mark Nicol, Martin Jones, David H. Persing, Doris Hillemann, Sabine Ruesch-Gerdes, Felicity Leisegang, Carlos Zamudio, Camilla Rodrigues, Catharina C. Boehme, Mark D. Perkins, David Alland

Research output: Contribution to journalArticle

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Abstract

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. Bacterialburden 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 we recompared 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 = 20.77) and directly from sputum (r s = -0.71). 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 = 0.68) andsemiquantitative colony counts (r s = -0.56)wasweaker than smear. Tests of paired same-patient sputum showed that highviscosity sputum samples contained x32 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 inmicroscopy. Conclusions: Xpert MTB/RIF quantitation offers a new, standardized approach to measuring bacterial burden in the sputum of patients with tuberculosis.

Original languageEnglish (US)
Pages (from-to)1076-1084
Number of pages9
JournalAmerican journal of respiratory and critical care medicine
Volume184
Issue number9
DOIs
StatePublished - Nov 1 2011

Fingerprint

Mycobacterium tuberculosis
Sputum
Real-Time Polymerase Chain Reaction
Microscopy
Bacterial Load
Infection Control
Bacillus
Tuberculosis
Biomarkers
Clinical Trials
Acids

All Science Journal Classification (ASJC) codes

  • Pulmonary and Respiratory Medicine
  • Critical Care and Intensive Care Medicine

Keywords

  • Clinical trial
  • Diagnosis
  • Diagnostic techniques and procedures
  • Molecular diagnostics
  • Tuberculosis

Cite this

Blakemore, Robert ; Nabeta, Pamela ; Davidow, Amy L. ; Vadwai, Viral ; Tahirli, Rasim ; Munsamy, Vanisha ; Nicol, Mark ; Jones, Martin ; Persing, David H. ; Hillemann, Doris ; Ruesch-Gerdes, Sabine ; Leisegang, Felicity ; Zamudio, Carlos ; Rodrigues, Camilla ; Boehme, Catharina C. ; Perkins, Mark D. ; Alland, David. / A multisite assessment of the quantitative capabilities of the Xpert MTB/RIF assay. In: American journal of respiratory and critical care medicine. 2011 ; Vol. 184, No. 9. pp. 1076-1084.
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abstract = "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. Bacterialburden 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 we recompared 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 = 20.77) and directly from sputum (r s = -0.71). 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 = 0.68) andsemiquantitative colony counts (r s = -0.56)wasweaker than smear. Tests of paired same-patient sputum showed that highviscosity sputum samples contained x32 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 inmicroscopy. Conclusions: Xpert MTB/RIF quantitation offers a new, standardized approach to measuring bacterial burden in the sputum of patients with tuberculosis.",
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author = "Robert Blakemore and Pamela Nabeta and Davidow, {Amy L.} and Viral Vadwai and Rasim Tahirli and Vanisha Munsamy and Mark Nicol and Martin Jones and Persing, {David H.} and Doris Hillemann and Sabine Ruesch-Gerdes and Felicity Leisegang and Carlos Zamudio and Camilla Rodrigues and Boehme, {Catharina C.} and Perkins, {Mark D.} and David Alland",
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Blakemore, R, Nabeta, P, Davidow, AL, Vadwai, V, Tahirli, R, Munsamy, V, Nicol, M, Jones, M, Persing, DH, Hillemann, D, Ruesch-Gerdes, S, Leisegang, F, Zamudio, C, Rodrigues, C, Boehme, CC, Perkins, MD & Alland, D 2011, 'A multisite assessment of the quantitative capabilities of the Xpert MTB/RIF assay', American journal of respiratory and critical care medicine, vol. 184, no. 9, pp. 1076-1084. https://doi.org/10.1164/rccm.201103-0536OC

A multisite assessment of the quantitative capabilities of the Xpert MTB/RIF assay. / Blakemore, Robert; Nabeta, Pamela; Davidow, Amy L.; Vadwai, Viral; Tahirli, Rasim; Munsamy, Vanisha; Nicol, Mark; Jones, Martin; Persing, David H.; Hillemann, Doris; Ruesch-Gerdes, Sabine; Leisegang, Felicity; Zamudio, Carlos; Rodrigues, Camilla; Boehme, Catharina C.; Perkins, Mark D.; Alland, David.

In: American journal of respiratory and critical care medicine, Vol. 184, No. 9, 01.11.2011, p. 1076-1084.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A multisite assessment of the quantitative capabilities of the Xpert MTB/RIF assay

AU - Blakemore, Robert

AU - Nabeta, Pamela

AU - Davidow, Amy L.

AU - Vadwai, Viral

AU - Tahirli, Rasim

AU - Munsamy, Vanisha

AU - Nicol, Mark

AU - Jones, Martin

AU - Persing, David H.

AU - Hillemann, Doris

AU - Ruesch-Gerdes, Sabine

AU - Leisegang, Felicity

AU - Zamudio, Carlos

AU - Rodrigues, Camilla

AU - Boehme, Catharina C.

AU - Perkins, Mark D.

AU - Alland, David

PY - 2011/11/1

Y1 - 2011/11/1

N2 - 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. Bacterialburden 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 we recompared 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 = 20.77) and directly from sputum (r s = -0.71). 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 = 0.68) andsemiquantitative colony counts (r s = -0.56)wasweaker than smear. Tests of paired same-patient sputum showed that highviscosity sputum samples contained x32 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 inmicroscopy. Conclusions: Xpert MTB/RIF quantitation offers a new, standardized approach to measuring bacterial burden in the sputum of patients with tuberculosis.

AB - 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. Bacterialburden 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 we recompared 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 = 20.77) and directly from sputum (r s = -0.71). 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 = 0.68) andsemiquantitative colony counts (r s = -0.56)wasweaker than smear. Tests of paired same-patient sputum showed that highviscosity sputum samples contained x32 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 inmicroscopy. Conclusions: Xpert MTB/RIF quantitation offers a new, standardized approach to measuring bacterial burden in the sputum of patients with tuberculosis.

KW - Clinical trial

KW - Diagnosis

KW - Diagnostic techniques and procedures

KW - Molecular diagnostics

KW - Tuberculosis

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