A multisite assessment of the quantitative capabilities of the Xpert MTB/RIF assay.
Am J Respir Crit Care Med
; 184(9): 1076-84, 2011 Nov 01.
Article
em En
| MEDLINE
| ID: mdl-21836139
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. 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 MAINRESULTS:
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) = -0.77) 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) and semiquantitative colony counts (r(s) = -0.56) was weaker than smear. Tests of paired same-patient sputum showed that high viscosity sputum samples contained ×32 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.
Texto completo:
1
Eixos temáticos:
Pesquisa_clinica
Base de dados:
MEDLINE
Assunto principal:
Escarro
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Tuberculose
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Técnicas de Amplificação de Ácido Nucleico
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Microscopia
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Mycobacterium tuberculosis
Tipo de estudo:
Clinical_trials
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Diagnostic_studies
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Prognostic_studies
Limite:
Humans
Idioma:
En
Ano de publicação:
2011
Tipo de documento:
Article