Uitlity of MODS for the Diagnosis of MDR-TB and Second-Line Antituberculous Drug Susceptibility Testing in Mali

Approximately one-third of the world s population is infected with tuberculosis (TB), and over 1 million deaths occur annually worldwide because of it (1,2). Accurate diagnosis and TB drug susceptibility testing is necessary to treat the infection appropriately and bring this epidemic under control. Inappropriate treatment of TB, on the other hand, has led to the recent spread in multidrug-resistant TB (MDR-TB), estimated to affect over half of million people worldwide (2,4,5). Sputum smear microscopy, the diagnostic method commonly used in developing countries, is not as sensitive at detecting TB as culture-based techniques utilized in developed countries. Furthermore, drug-susceptibility testing is not routinely performed in resource-limited settings. Consequently, many individuals with TB in developing countries are treated with inadequate regimens, and MDR-TB continues to spread.

The microscopic-observation drug-sensitivity (MODS) assay has been recently developed for rapid diagnosis of TB and simultaneous detection of resistance to first-line TB medications in resource-limited settings (11). MODS has been shown to be as sensitive as traditional culturebased methods for the detection of TB, providing results for drug susceptibility testing that are highly concordant with standard techniques (10).

We propose to study the utility of the MODS assay for the diagnosis of TB in subjects who are sputum-smear positive or sputum-smear negative, and those with chronic TB. Susceptibility testing will be performed for first-line antituberculous drugs and, subsequently, second-line drugs, if subjects are found to have MDR-TB. The first primary objective is to calculate the sensitivity of detection of the MODS assay, compared with the Middlebrook culture method, in subjects suspected of having TB who are sputum-smear positive by microscopy. The second primary objective is to calculate the concordance of drug-susceptibility testing between the MODS assay and the agar proportion method for subjects who are sputum-smear positive, sputum-smear negative, or diagnosed with chronic TB.

Secondary objectives include evaluating the utility of the MODS assay in the diagnosis of TB in subjects who are sputum-smear negative and those with chronic TB, the performance of second-line drug-susceptibility testing using the MODS assay in subjects diagnosed with MDRTB, the utility of the MODS assay in the diagnosis of TB in subjects coinfected with human immunodeficiency virus (HIV)-1 or -2, and the ability of the MODS assay to identify nontuberculous mycobacteria in subjects harboring these organisms.