MDR-TB Test Produces Rapid, Accurate Results, Study Says

A new molecular test aimed at detecting multi-drug resistant tuberculosis can produce fast and accurate results, according to a study published in the April issue of the American Journal of Respiratory and Clinical Care Medicine, South Africa's Times reports. The test could lead to earlier access to appropriate treatment, successful treatment of MDR-TB and the prevention of extensively drug-resistant TB, which is resistant to the two most potent first-line treatments and at least two of the classes of second-line drugs, Gerrit Coetzee, a study author and head of South Africa's National Tuberculosis Reference Laboratory, said (Keeton, Times, 4/6).

For the study, the scientists examined the molecular test's performance and feasibility of implementation for the rapid detection of rifampicin and isoniazid resistance. Although the test is commercially available, it is not widely used in most areas with high TB burdens, according to the authors. The researchers tested 536 smear-positive sputum specimens taken from people who were determined to be at an increased risk of MDR-TB. They compared the results with conventional liquid culture and drug-susceptibility testing.

The study found that the molecular test provided interpretable results within one or two days for 97% of smear-positive specimens. Sensitivity, specificity, and positive and negative predictive values were 98.8%, 100%, 100% and 99.7%, respectively, for the detection of MDR-TB compared with conventional results. The test also performed well on specimens that were contaminated on conventional culture and on smear-negative, culture-positive specimens, according to the authors. The researchers concluded that the test accelerates the diagnostic process for MDR-TB and that it produces highly accurate results that are better than conventional testing (Barnard et al., AJRCCM, April 2008).

"Patients can now be identified to have MDR-TB within a few days, instead of the many months it took previously," Coetzee said. Experts said the test could change the way MDR-TB is diagnosed, as well as efforts aimed at preventing the spread of the disease (Times, 4/6).

An abstract of the study is available online.