April 19, 2011.
Test for Mycobacterium tuberculosis, rifampicin resistance shows high sensitivity and specificity
Diagnosis of Mycobacterium tuberculosis (MTB) and rifampicin resistance (RIF), detected by the MTB/RIF test, is accurate and feasible in resource-poor countries, according to a study published online April 19 in The Lancet.
Diagnosis of Mycobacterium tuberculosis (MTB) and rifampicin resistance (RIF), detected by the MTB/RIF test, is accurate and feasible in resource-poor countries, according to a study published online April 19 in The Lancet.
Catharina C. Boehme, M.D., from the Foundation for Innovative New Diagnostics in Geneva, Switzerland, and colleagues evaluated whether the Xpert MTB/RIF test was feasible, robust, and accurate. Between 2009 and 2010, sputum smears and cultures of 6,648 tuberculosis patients were collected, and one-off direct MTB-RIF testing was compared to other detection methods. Indicators of robustness included indeterminate rate and between-site performance. The time to detection, reporting, treatment, and patient dropouts were compared between different tuberculosis-detection techniques.
The investigators found that one-off MTB/RIF testing detected 90.3 percent of 1,033 culture-confirmed tuberculosis cases, and microscopy detected 67.1 percent of 1,041 cases. The MTB/RIF test was 76.9 percent sensitive and 99.0 percent specific for smear-negative, culture-positive patients. Test sensitivity was 94.4 percent and specificity was 98.3 percent for rifampicin resistance. In contrast to microscopy, test sensitivity did not decrease significantly in patients with HIV co-infection. Average tuberculosis detection time was zero days for MTB/RIF, one day for microscopy, and 30 and 16 days for solid and liquid cultures, respectively. Average resistance detection time was 20 and 106 days for line-probe assay and conventional drug-susceptibility test, respectively. The MTB/RIF test reduced the average treatment time from 56 to five days for smear-negative tuberculosis. The indeterminate rate was 2.4 and 4.6 percent for MTB/RIF and cultures, respectively.
"Our findings suggest that decentralized MTB/RIF test implementation is feasible and could lead to an improvement in tuberculosis care and control," the authors write.
Several study authors disclosed financial relationships with Cepheid, which developed the MTB/RIF test and partially funded the study.
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