Prospective evaluation of simply modified MODS assay: an effective tool for TB diagnosis and detection of MDR-TB

Thailand is one of the highest tuberculosis (TB)-burdened countries. Chiang Rai, the northernmost province of Thailand has high tuberculosis and human immunodeficiency virus (HIV) prevalence and the laboratory workload for TB culture and drug susceptibility testing is increasing.

To evaluate the simply modified microscopic-observation drug-susceptibility assay (MODS) in the setting of a developing country.

In this cross-sectional diagnostic study, a total of 202 sputum samples of clinically diagnosed TB patients were used to test the performance of MODS assay in reference to gold standard BACTEC™ MGIT™ 960 liquid culture system and Ogawa solid culture. Sputum samples were collected from clinically diagnosed TB patients. Culture growth rate and time to culture positivity were compared among three methods. Performance of modified MODS assay was evaluated for detection of mycobacterium drug resistance in reference to MGIT antimicrobial susceptibility test (AST).

Median time to culture positivity by MODS, solid, and liquid culture were 12, 30, and 6 days respectively. Compared to the drug susceptibility test (DST) result of reference liquid culture, the sensitivity and specificity of MODS for detection of multidrug-resistant tuberculosis (MDR-TB) was 85.7% and 97.5% respectively. MODS assay has a positive predicative value of 80% and negative predictive value of 96.5% for isoniazid resistance, 70% and 100% for rifampicin resistance, and 66.7% and 99.1% for MDR-TB.

MODS is a highly effective screening test for detection of MDR-TB.