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Review
. 2011 Sep;6(9):1067-82.
doi: 10.2217/fmb.11.84.

Xpert® MTB/RIF assay: development, evaluation and implementation of a new rapid molecular diagnostic for tuberculosis and rifampicin resistance

Stephen D Lawn  1 , Mark P Nicol
Affiliations
Review

Xpert® MTB/RIF assay: development, evaluation and implementation of a new rapid molecular diagnostic for tuberculosis and rifampicin resistance

Stephen D Lawn et al. Future Microbiol. 2011 Sep.

Erratum in

  • Future Microbiol. 2012 Aug;7(8):1024

Abstract

Global TB control efforts have been severely hampered by the lack of diagnostic tests that are accurate, simple to use and can be applied at the point of clinical care. This has been further compounded by the widespread inability to test for drug resistance. The Xpert(®) MTB/RIF assay is a rapid molecular assay that can be used close to the point of care by operators with minimal technical expertise, enabling diagnosis of TB and simultaneous assessment of rifampicin resistance to be completed within 2 h. Moreover, this can be accomplished using unprocessed sputum samples as well as clinical specimens from extrapulmonary sites. We review in detail the development of this assay, its evaluation within the laboratory, its utility among adult and pediatric TB suspects, its use as a screening tool for HIV-associated TB and studies of its implementation at the district and sub-district levels in resource-limited settings. Following endorsement by the WHO in 2010, we consider the next steps in the implementation of the assay and its potential impact in high burden settings.

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Figures

Figure 1
Figure 1. The rpoB gene core region target sequence and molecular beacon technology
(A) The rpoB gene, the nucleotide sequence of the core region and the localization of the complementary overlapping molecular beacon probes that span the complete core region. (B) The stem-and-loop structure of a molecular beacon and onset of fluorescence following binding to a complementary DNA strand. The loop structure of the molecular beacon contains the complementary oligonucleotide probe sequence, and the fluorophore and quencher molecules are attached to the ends of the stem structure. Following hybridization, conformational change in the probe leads to separation of the fluorophore and quencher molecules and onset of fluorescence.
Figure 2
Figure 2. Various steps within the Xpert® MTB/RIF assay procedure
SR: Sample reagent. Diagram supplied by C Boehme, Foundation for Innovative New Diagnostics.
Figure 3
Figure 3. GeneXpert user view of the amplified probes A-E and the sample processing control
Trace (A) shows the read-out from processing a rifampicin-sensitive strain of Mycobacterium tuberculosis as denoted by amplification of all five probes with a similar cycle threshold. Trace (B) shows the read-out of a rifampicin-resistant strain as shown by the failure of amplification of Probe B. SPC: Sample processing control.
Figure 4
Figure 4. The sensitivity (95% CI) of Xpert® MTB/RIF assay for smear-positive and smear-negative TB according to whether 1, 2 or 3 sputum samples were tested compared to a gold standard of four cultures from two sputum samples
Data taken from the FIND multicountry laboratory validation study [11].
Figure 5
Figure 5. Photograph showing the Xpert® MTB/RIF assay being used in a peripheral health facility
Courtesy of National Health Laboratory Service of South Africa.
See this image and copyright information in PMC

References

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MeSH terms