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Abstract
The lack of capacity to provide laboratory confirmation of a diagnosis of tuberculosis disease (TB) is contributing to enormous gaps in the ability to find, treat and follow TB patients. WHO estimates that globally only about 57% of the notified new cases of pulmonary TB in 2012 and about 19% of rifampicin-resistant TB cases were laboratory confirmed. The Cepheid Xpert® MTB/RIF assay has been credited with revolutionizing laboratory testing to aid in the diagnosis of TB and rifampicin-resistant TB. This semi-automated test can detect both the causative agent of TB and mutations that confer rifampicin resistance from clinical specimens within 2 h after starting the test. In this article, we review the performance of the test, its pathway to regulatory approval and endorsement, guidelines for its use and lessons learned from the implementation of the test in low-burden, high-resource countries and in high-burden, low-resource countries.
Acknowledgements
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the US CDC.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.
No writing assistance was utilized in the production of this manuscript.
The definitive diagnosis of tuberculosis (TB) relies on laboratory testing to detect the presence of the causative agent (Mycobacterium tuberculosis complex bacteria, MTBC).
Only about 57% of the estimated 4.57 million notified cases of pulmonary TB in 2012 and about 19% of rifampicin-resistant TB cases were laboratory confirmed, which indicate enormous gaps in the ability to find, treat and follow TB patients.
The Cepheid Xpert® MTB/RIF assay (Xpert MTB/RIF) has the potential to revolutionize laboratory testing to aid in the diagnosis of TB and rifampicin-resistant TB.
Xpert MTB/RIF can detect both MTBC and rifampicin resistance from clinical specimens within 2 h after starting the test, with minimal hands-on time and minimal requirements for facilities.
A single Xpert MTB/RIF has sensitivity and specificity equivalent to a single culture on solid media for detecting MTBC, which may increase TB case detection by 30–40% in settings where laboratory confirmation relies on direct acid-fast bacilli smear microscopy.
However, conventional culture and drug-susceptibility test is still needed to detect MTBC in acid-fast bacilli-negative samples, confirm rifampicin resistance in persons at low risk of having MDR TB and determining susceptibilities to other drugs.
As is true for all tests, clinicians should interpret any laboratory result on the basis of the clinical situation.
The impact of Xpert MTB/RIF on clinical care and public health will vary according to the epidemiologic setting, target population (e.g., all patients with TB disease, patients with HIV-associated TB or patients with MDR TB), current testing and treatment algorithms and Xpert MTB/RIF testing algorithms.
– In settings that rely on AFB microscopy, the use of Xpert MTB/RIF can increase case detection and reduce time to initiation of appropriate therapy, particularly for patients with MDR TB.
– In settings that rely on clinical findings to initiate therapy, the use of Xpert MTB/RIF is likely to have much less effect on case finding and time to initiation of therapy.
Xpert MTB/RIF has been approved by the FDA for use in the USA, received Conformité Européene marking and endorsed by WHO for use in TB-endemic countries.