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

Abstract

Background and setting

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.

Objectives

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

Methods

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).

Result

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.

Conclusion

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

Keywords:

• tuberculosis
• drug resistance
• MODS assay
• Chiang Rai
• Thailand

Acknowledgments

This work was sponsored partly by Research Institute of Tuberculosis, Japan. David AJ Moore is acknowledged for his technical advice. Hideki Yani is acknowledged for his suggestions and research protocol comments. Nurses, medical technologists and TB clinic staff of 17 hospitals in Chiang Rai province are acknowledged for their cooperative assistance.

Authors' contribution

Norio Yamada, Myo Nyein Aung, Saiyud Moolphate and Boonchai Chaiyasirinroje designed the study. Myo Nyein Aung developed the research proposal which was edited by Norio Yamada, Satoshi Mitarai, Somsak Rienthong, and Dhanida Rienthong in October 2009. Myo Nyein Aung and Boonchai Chaiyasirinroje developed the standard operating procedures for the study in November 2009. Boonchai Chiyasirinrote carried out all the TB cultures and MODS procedures with the help of Oranuch Nampaisan. Supalert Nedsuwan, Wiravoot Sangchun, and Narin Suriyon contributed to the research process and collection of data. Saiyud Moolphate and Myo Nyein Aung analyzed the data and interpreted the results. Myo Nyein Aung wrote the manuscript. Norio Yamada, Somsak Rienthong, Yuthichai Kasetjaroen, Dhanida Rienthong, Satoshi Mitarai and Boonchai Chaiyasirinroje critically reviewed, revised, and amended the manuscript. All the authors contributed their comments which have been amalgamated into the final manuscript by Myo Nyein Aung.

Disclosure

The authors declare no conflict of interest in this work.