Extract
To the Editor:
Although drug susceptible tuberculosis (TB) is a curable disease, spread of rifampicin-resistant TB, including multidrug-resistant (MDR)- and extensively drug-resistant (XDR)-TB, is a threat to disease control worldwide [1], in particular in Eastern Europe [2]. XpertMTB/RIF (Xpert; Cepheid Inc., Sunnyvale, CA, USA) is an accurate [3] and affordable [4] automated PCR-based assay that detects DNA of Mycobacterium tuberculosis and resistance to rifampicin in <2 h [5].
While the World Health Organization (WHO) has endorsed the use of Xpert for TB diagnosis as a replacement for sputum smear examination [6], concerns have been raised about the low positive predictive value (PPV) of rifampicin-resistant Xpert results in patients who have never previously been treated for TB and in countries with a low prevalence of rifampicin-resistance and MDR-TB [5]. WHO guidelines currently call for initiation of MDR-TB treatment with second-line drugs when resistance is repeatedly detected by Xpert, while confirmatory testing is performed [6].
Xpert detects mutations in the M. tuberculosis rpoB gene, which is responsible for >95% of rifampicin resistance, with a well-established 98% specificity [3, 7]. Compared with the earlier version [3, 7], the latest generation (G4) assay has a reduced risk of false positive results for rifampicin resistance [8]. The probe B sequence was
- Received June 24, 2014.
- Accepted July 24, 2014.
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