Assay for Tuberculosis Shows Promise in Low-Income Areas

Test simple to perform, has high sensitivity in smear-negative cases of disease
By Eric Metcalf
HealthDay Reporter

THURSDAY, Sept. 2 (HealthDay News) -- An automated molecular test for Mycobacterium tuberculosis (MTB) and resistance to rifampin (RIF) -- Xpert MTB/RIF -- allows for rapid and sensitive detection of tuberculosis and rifampin resistance, according to research published online Sept. 1 in the New England Journal of Medicine.

Catharina C. Boehme, M.D., of the Foundation for Innovative New Diagnostics in Geneva, and colleagues analyzed data from 1,730 patients with suspected pulmonary tuberculosis, either drug-sensitive or multi-drug-resistant, in Peru, South Africa, India, and Azerbaijan. Each provided three sputum specimens for different processing, including direct testing with microscopy and the MTB/RIF test.

The researchers found that, among culture-positive individuals, a single, direct MTB/RIF test identified 98.2 percent of those with smear-positive tuberculosis. For smear-negative, culture-positive tuberculosis, its sensitivity was 72.5 percent for one test, 85.1 percent for two, and 90.2 percent for three. The test was specific in 99.2 percent of those without tuberculosis. Compared to phenotypic drug-susceptibility testing, the MTB/RIF test identified 97.6 percent of patients with rifampin-resistant tuberculosis and 98.1 percent with rifampin-sensitive tuberculosis.

"Issues involving the MTB/RIF assay may limit its global utility. These issues include its high cost, limitations in testing only for rifampin resistance, a platform that detects a relatively small number of mutations, and [an] inability to indicate which patients are 'sputum smear-positive' for reporting purposes, infection-control intervention, and treatment monitoring," write the authors of an accompanying editorial.

The study was supported by Cepheid, which employs two co-authors.

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