n engl j med 356;2 www.nejm.org january 11, 2007 188 The new england journal of medicine correspondence MODS Assay for the Diagnosis of TB To the Editor: In their article on the use of mi- croscopic-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 gold- standard 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 described 2 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 mi- croscopes, had better results than conventional methods when evaluated in target populations. 4 In ongoing evaluations, the thin-layer agar meth- od has also outperformed the reference method for detecting multidrug-resistant tuberculosis. In addition, direct colorimetric methods with redox indicators have performed very well 5 and are under further evaluation. A disadvantage of the MODS method remains the requirement of an inverted microscope, which is not routinely avail- able 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 jcpalomino@itg.be Moore DAJ, Evans CAW, Gilman RH, et al. Microscopic- observation drug-susceptibility assay for the diagnosis of TB. N Engl J Med 2006;355:1539-50. Palomino JC. Newer diagnostics for tuberculosis and multi- drug resistant tuberculosis. Curr Opin Pulm Med 2006;12:172-8. Musa HR, Ambroggi M, Souto A, Angeby KA. Drug suscep- tibility testing of Mycobacterium tuberculosis by a nitrate reduc- tase assay applied directly on microscopy-positive sputum sam- ples. J Clin Microbiol 2005;43:3159-61. Robledo JA, Mejia GI, Morcillo N, et al. Evaluation of a rapid culture method for tuberculosis diagnosis: a Latin American multi-center study. Int J Tuberc Lung Dis 2006;10:613-9. Abate G, Aseffa A, Selassie A, et al. Direct colorimetric assay for rapid detection of rifampin-resistant Mycobacterium tubercu- losis. J Clin Microbiol 2004;42:871-3. To the Editor: The MODS assay has certain lim- itations. Microscopical differentiation between mi- crocolonies of Mycobacterium tuberculosis and those of rapidly growing mycobacteria may be difficult. The assay requires daily examination, is time- consuming, and as highlighted by Iseman and Heifets, 1 carries a risk of laboratory transmission. We therefore agree that the microscopical-obser- vation method, although promising, will require modification and adaptation before it can be rec- ommended for widespread use. Rumina Hasan, M.B., B.S., Ph.D. Seema Irfan, M.B., B.S. Aga Khan University Karachi 74800, Pakistan rumina.hasan@aku.edu Iseman MD, Heifets LB. Rapid detection of tuberculosis and drug-resistant tuberculosis. N Engl J Med 2006;355:1606-8. 1. 2. 3. 4. 5. 1. this week’s letters 188 MODS Assay for the Diagnosis of TB 189 Refining Prognosis in Non–Small-Cell Lung Cancer 191 Survivors of Childhood Cancer 194 A Girl with Severe Obesity 196 Injuries after a Typhoon in China 197 Prisons and Mental Health Downloaded from www.nejm.org on January 10, 2007 . Copyright © 2007 Massachusetts Medical Society. All rights reserved.