Molecular test detects tuberculosis, screens for rifampin resistance

In response to a need for simple and rapid diagnostic tools for tuberculosis in high-burden countries, investigators assessed the performance of Xpert MTB/RIF, a fully automated molecular test, for the presence of Mycobacterium tuberculosis (MTB) and resistance to rifampin in 1,730 patients with suspected drug-sensitive or multidrug-resistant pulmonary tuberculosis. The trial was conducted at 5 sites in Peru, Azerbaijan, South Africa, and India.

The MTB/RIF test uses a real-time polymerase chain reaction (PCR) assay to amplify an MTB-specific sequence of the rpoB gene, which is probed with molecular beacons for mutations within the rifampin-resistance-determining region. Results of the MTB/RIF test can be obtained within 2 hours.

Three sputum samples were obtained from each patient. Two specimens were processed with N-acetyl-L-cysteine and sodium hydroxide before microscopy, solid and liquid culture, and the MTB/RIF test. The third specimen was used for direct testing with microscopy and the MTB/RIF test.

Commentary

This is an exciting article because it demonstrates use of PCR and genetic sequencing at the bedside (or in the clinic), not just in the industrialized world but where it is needed most, in developing countries. The researchers look carefully at the practicality of using this technology in high-prevalence tuberculosis areas. They demonstrate that it can be done and discuss how this rapid, more accurate diagnostic testing could improve care and reduce resistance. -Michael Burke, MD