Microscopic observation drug susceptibility [MODS] as a rapid, simple low-cost diagnostic tool in cases with MDR tuberculosis

ABSTRACT

Multidrug resistant tuberculosis [MDR-TB], which is tuberculosis [TB] resistant to at least isoniazid and rifampicin, is a major threat to TB control worldwide. Early detection of MDR-TB allows initiation of an appropriate treatment. Diagnosis of MDR-TB requires microbiologic evaluation of the Mycobacterium tuberculosis isolates drug susceptibility. The microscopic observation drug susceptibility [MODS] is a relatively low-cost, simple liquid culture method that relies on the microscopic detection of cording growth that is characteristic of Mycobacterium tuberculosis. We undertook a prospective study to evaluate the performance of MODS. Testing for the direct detection of M. tuberculosis drug resistance in specimen from patients with suspected pulmonary TB at risk for drug resistance. The study was carried out on 150 individuals. Samples at risk for drug resistance were cultured positive for M. tuberculosis by both MODS and LJ. methods. By the comparator LJ. testing method, 57 isolates [38.0%] were resistant to both INH and RIF, 19 [12.7%] were resistant to INH alone, 4 [2.7%] were RIF monoresistant, and 70 [46.6%] were susceptible to both INH and RIF. The performance parameters of the MODS assay are shown. MODS test results are shown for undiluted MODS inocula and for inocula diluted 110. The MODS assay indicated some specimens to be resistant than the comparator method indicated to be susceptible. This trend was slightly more marked when undiluted inocula were used for MODS. The time interval of 14 days was chosen as the susceptibility or resistance status indicated by the MODS assay is stable for at least 2 weeks after the detection of growth and because this strategy optimized efficiency by eliminating the need for daily microscopic examination of all drug-containing wells. Median times to the availability of susceptibility results were 21 days [interquartile range, 17 to 24 days] for the MODS method and 49 days [interquartile range, 46 to 55 days] for the LJ. method [P, <0.001 by paired t tes]