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Canadian Journal of Infectious Diseases and Medical Microbiology
Volume 19 (2008), Issue 2, Pages 169-172
Special Article

Diagnosis of Multidrug-Resistant Tuberculosis and Extensively Drug-Resistant Tuberculosis: Current Standards and Challenges

Giovanni Battista Migliori,1 Alberto Matteelli,2 Daniela Cirillo,3 and Madhukar Pai4

1WHO Collaborating Centre for TB and Lung Diseases, Fondazione S Maugeri, Care and Research Institute, Tradate, Italy
2Institute of Infectious and Tropical Diseases, University of Brescia, Italy
3Supranational Reference Laboratory, S Raffaele Institute, Milano, Italy
4McGill University and Montreal Chest Institute, Montreal, Quebec, Canada

Received 27 November 2007; Accepted 18 January 2008

Copyright © 2008 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


INTRODUCTION: The emergence of multidrug-resistant tuberculosis (MDR-TB) and, more recently, extensively drug-resistant TB (XDR-TB) is widely considered a serious threat to global TB control. Over 400,000 new cases of MDR-TB occur each year and, although their rates are currently unknown, XDR-TB cases have been detected in every country where there is capacity to detect them (including Canada).

METHODS: The present article provides a narrative overview of the various diagnostic options available for XDR-TB, including conventional tools and newer rapid tests for drug resistance. Available data suggest that automated liquid cultures are highly accurate and their use is rapidly expanding. Newly developed phenotypic tests include TK Medium (Salubris Inc, USA), microscopic-observation drug-susceptibility assay, FASTPlaque-Response bacteriophage assay (Biotec Laboratories Ltd, UK), colorimetric redox indicator methods and the microcolony method. These tests are usually cheaper but not always simple to perform, with some requiring high standards of biosafety and quality control. Among the newly developed phenotypic methods, reverse hybridization-based assays, referred to as line probe assays, represent a useful tool because of their superior accuracy and cost-effectiveness.

CONCLUSIONS: To effectively address the threats of MDR-TB and XDR-TB, global initiatives are required to scale-up culture and drug susceptibility testing capacities, especially in high-burden countries where such capacity is scarce. In parallel, efforts are needed to expand the use of novel and emerging technologies (ie, molecular diagnostics) for the rapid determination of drug resistance.