Microscopic-observation drug susceptibility assay provides rapid and reliable identification of MDR-TB.

Background: Liquid culture systems are more rapid and sensitive for both the detection and drug susceptibility testing (DST) of Mycobacterium tuberculosis. Methods: St Peter's TB Specialised Hospital and public health laboratory, Addis Ababa.

Objective: To compare the microscopic-observation drug susceptibility (MODS) assay with the BACTEC-MGIT 960 system for isoniazid and rifampicin DST (i.e., multidrug-resistant tuberculosis [MDR-TB] identification) of M. tuberculosis.

Methods: The evaluation was based on 58 smear- and culture-positive sputum samples from patients diagnosed in Addis Ababa, Ethiopia. BACTEC-MGIT was used as the reference standard.

Results: For the detection of MDR-TB, MODS has a sensitivity, specificity and accuracy rate of respectively 95%, 100% and 98.3% (kappa 0.981, concordance 98.3%). Concurrent culture detection and DST results are obtained in a median of 9 days with MODS, while indirect DST results with BACTEC-MGIT are obtained in a median of 8 days (this does not include time to primary isolate).

Conclusions: MODS is an accurate, rapid and relatively inexpensive method for the identification of MDR-TB.