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Rapid TB/MDR-TB test shown effective in resource-limited settings
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A new Mycobacterium tuberculosis and rifampin-resistant rapid test was effective in lower-resource settings and provided access to early and accurate treatment and decreased morbidity across sites in South Africa, Peru, India, Azerbaijan and the Philippines.
For the multicenter study, Catharina C. Boehme, MD, of the Foundation for Innovative New Diagnostics in Geneva, and colleagues assessed data among 6,648 adults aged 18 years and older with suspected TB or multidrug-resistant TB (MDR-TB) and cough lasting at least 2 weeks.
The researchers chose study sites to represent diverse populations and laboratory capacities. For example, sites in Uganda and South Africa served a high HIV population and sites in Azerbaijan and the Philippines served a high population of patients with MDR-TB. Conversely, sites in India and Peru served populations with a low prevalence of HIV and MDR-TB.
The operational feasibility, accuracy, and efficacy of the M. tuberculosis resistance to rifampin test (Xpert, Cepheid) in district and subdistrict health facilities were then compared with standard TB diagnostic methods. The study was divided into two phases: a validation phase (test results were not reported or used during this time) and an implementation phase (test results were reported and patietns were informed of TB treatment.)
Compared with a 67% detection rate with microscopy, more than 90% of patients had positive cultures with a 99% specificity for non-TB with the new rapid test. Overall, significantly more TB cases were identified with the new test compared with two to three smear microscopy examinations (P<.0001). Further, the sensitivity of smear microscopy was significantly decreased in patients coinfected with HIV (P<.0001), but sensitivity was not reduced with the new rapid test (P=.0849).
Median time to detection of TB was immediate with the new test compared with 1 day for microscopy, 16 days for liquid culture and 30 days for solid culture. Median time to treatment for smear-negative TB decreased from 56 days to 5 days with the new rapid test.
“Our findings suggest that decentralized rapid testing implementation is feasible and could lead to an improvement in TB care and control,” Boehme and colleagues wrote. “Any improvement will require increased detection of TB and MDR-TB to coincide with scale-up of first-line, and more importantly, second-line treatment. Whether early and appropriate treatment after rapid testing can reduce TB-associated morbidity and mortality, and its effect on transmission needs to be established.”
In an accompanying editorial, Katharina Kranzer, of the department of clinical research at the London School of Hygiene and Tropical Medicine in London, wrote that: “Although we acknowledge the achievement of the [new rapid] test, a diagnostic test with only 90% sensitivity for a potentially life-threatening disease is far from perfect. The device is still not the point-of-care test that health care providers desire: it needs electricity, operating temperatures of less than 30·C, and takes about 2 hours to process a sample. The instrument and the supplies are too expensive for most countries with a high burden of TB. The ideal rapid test for this disease needs to be affordable, sensitive, specific, user-friendly, rapid, robust, and equipment-free, and work for adults and children. Thus, research into new TB diagnostics must continue.”
For more information:
- Boehme CC. Lancet. 2011;doi:10.1016/S0140-6736(11)60438-8.
- Kranzer K. Lancet. 2011;doi:10.1016/S0140-6736(11)60513-8.
This study from the Foundation for Innovative New Diagnostics (FIND) and investigators from participating sites is an important addition to the growing body of knowledge about the performance characteristics of the Xprt MTB/RIF test for the rapid and accurate diagnosis of Mycobacterium tuberculosis and its susceptibility to rifampin. The test is a fully automated cartridge-based technique with real-time PCR on a direct sputum specimen, yielding a result in less than 2 hours. This represents a major technological advance over the insensitive sputum smear and for time-to-detection compared to standard mycobacterial culture and susceptibility testing. Importantly, the feasibility of using the test in district and subdistrict laboratories was demonstrated, with sensitivity and specificity similar to the prior studies that were conducted in central reference laboratories in resource-limited settings. The sites were purposely selected to be heterogeneous (ie, differing prevalence of HIV and MDR-TB), therefore, making the results more generalizable. This study and others led to the endorsement by WHO in December 2010 of Xprt MTB/RIF for use in high TB prevalence countries, followed by a well-attended and enthusiastic workshop in Geneva on early implementation and roll-out of the test. In the previously slow moving and underfunded field of TB research, the widespread and proper implementation of this diagnostic breakthrough, coupled with advances in TB treatment, should lead to significant improvement in global TB control.
– David Cohn, MD
Infectious Disease News Editorial Board member
Disclosure: Dr. Cohn reports no relevant financial disclosures
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