MODS assay for the diagnosis of TB.

To the Editor: In their article on the use of microscopic-observation drug-susceptibility (MODS) culture for the diagnosis and direct detection of multidrug-resistant tuberculosis, Moore et al. (Oct. 12 issue)1 state that MODS culture offers faster and more sensitive results than existing goldstandard methods. This study is one of the few performed in a target population with a rather simple and inexpensive method that seems to be appropriate for countries with limited resources. However, we would like to stress that there are other options that have recently been described2 and are currently under evaluation. As compared with MODS culture, the nitrate reduction assay, based on a simple procedure involving the use of Löwenstein–Jensen medium, has been tested in sputum samples with similarly good results.3 The thin-layer agar method, which is similar to MODS culture but with solid medium and standard microscopes, had better results than conventional methods when evaluated in target populations.4 In ongoing evaluations, the thin-layer agar method has also outperformed the reference method for detecting multidrug-resistant tuberculosis. In addition, direct colorimetric methods with redox indicators have performed very well5 and are under further evaluation. A disadvantage of the MODS method remains the requirement of an inverted microscope, which is not routinely available in laboratories that perform diagnostic tests for tuberculosis. Juan-Carlos Palomino, Ph.D. Anandi Martin, Ph.D. Francoise Portaels, Ph.D. Institute of Tropical Medicine 2000 Antwerp, Belgium [email protected]