Evaluation of Microscopic observation drug susceptibility (MODS) assay as a rapid, sensitive and inexpensive test for detection of tuberculosis and multidrug resistant tuberculosis.

BACKGROUND: Microscopic observation drug susceptibility (MODS) assay has been suggested as a low cost method for rapid, accurate detection of tuberculosis (TB) and multidrug resistant tuberculosis (MDR-TB).

METHODS: A total of 2424 samples collected from 1063 eligible patients of suspected pulmonary or extrapulmonary TB were subjected to MODS assay. Performance of MODS was compared with culture and drug susceptibility testing (DST) by conventional solid Lowenstein-Jensen (LJ) media or liquid Mycobacteria Growth Indicator Tube (MGIT) culture.

RESULTS: When compared to reference gold standard of positivity in either solid or liquid reference culture, the MODS assay had sensitivity, specificity, positive predictive value and negative predictive value of 91.3%, 98.2%, 96.0% and 95.9% respectively. MODS took a median time of 10.3 days to culture positivity as compared to 13.8 days using MGIT and 30.5 days using LJ culture. Culture and DST being concurrent in MODS, the median turnaround time for DST was the same as that for culture i.e. 10.3 days. The overall median turn around time for culture positivity and DST using manual MGIT and LJ medium was 23.6 days and 61.2 days respectively. The concordance between MODS culture and the reference susceptibility method was 97.7% for rifampicin, 95.6% for isoniazid, 98.5% for rifampicin and isoniazid. The cost of performing a single MODS assay was INR 200.

CONCLUSION: MODS is a rapid and sensitive, yet simple and inexpensive test that may be helpful to enhance diagnostic accuracy, and case detection of TB and MDR-TB in resource constrained settings.