Multi-drug resistant M. tuberculosisis a growing concern in the Philippines, thus, a reliable, low cost diagnostic tool for the detection of MTB in clinical specimens is needed for early diagnosis. We aimed to compare the performance of MODS assay in the detection of MTB and MDR-TB from sputum specimens with the standard solid and liquid cultures.
We included a total of 795 specimens for the study from January 2012 to November 2013 from suspected TB patients from the outpatient department and those referred by the Programmatic Management of Drug Resistant Tuberculosis. AFB smears were done to all specimens using Ziehl-Neelsen staining method. After routine digestion, samples were inoculated onto LJ culture, MB BacT Culture System and MODS Assay and were monitored for growth. MODS assay was prepared in a 48-well tissue culture plastic plates and positive cultures were identified by its characteristic cord formation. Indirect agar-based disk submerged Proportion Method13 was done for all positive LJ cultures and MB BacT Culture System using critical drug concentrations: 0.2µg/ml for Isoniazid and 1µg/ml for Rifampicin. Direct drug susceptibility testing was performed for MODS assay using Isoniazid, 0.2 µg/ml and Rifampicin, 1 µg/ml. The culture plates were examined under an inverted microscope at 40X magnification daily for 15 days and twice weekly thereafter up to 40thday of incubation.
Out the 795 specimens analyzed, 269 specimens were smear negative and 526 were smear positive for AFB. MODS detected 60.9% specimens positive for MTB whereas LJ and MBact detected 46% and 60.4% respectively. MODS was able to detect 20% of the specimens as early as first week of incubation, one week earlier than the MBacT and three weeks than LJ. In detecting MDRTB, MODS has a sensitivity of 96.1% in smear positive specimens and a specificity of 99.5%, and it has 100% sensitivity and specificity for smear negative samples. Of the241 samples from recruited patients with on-going treatment, MTB can be isolated in all techniques, and 40-80% of the isolates were MDR regardless of smear result.
Conclusion: In a resource-limited country with a high burden of TB, MODS assay provides an inexpensive, sensitive and rapid technology. Culture and susceptibility results are given concurrently thus patients are treated earlier especially those with MDRTB.
J. Itable, None
R. Zamora, None