Early Detection of Multi-drug Resistant Tuberculosis and Mutations in Mycobacterium tuberculosis isolates using Line Probe Assay from a Tertiary Care Centre in Northern India DC19-DC24
Dr. Nargis Bali,
Sher-i-Kashmir Institute of Medical Sciences, Soura, Srinagar, Jammu and Kashmir, India.
Introduction: Early detection and drug susceptibility analysis of Mycobacterium tuberculosis (MTB) in the shortest possible time has been the driving force for research that aims to bridge the gap between detection and treatment. In this regard Line Probe Assays (LPA) were commissioned in 2008 by World Health Organisation (WHO) as an addition in the long list of diagnostic tools for MTB.
Aim: To assess the utility of LPA for the detection of Multi Drug Resistant Tuberculosis (MDR-TB) and to find out the most common mutations associated with it.
Materials and Methods: This cross-sectional prospective study was carried out in the Department of Microbiology, Government Medical College, Srinagar, Jammu and Kashmir, India; for a period of 18 months from November 2016 till May 2018. Two hundred and fifty two smear positive sputum samples and 100 randomly selected smear negative samples were subjected to LPA and cultured on Loweinstein Jensen (LJ) medium. MTB was confirmed taking into account colony morphology on LJ medium, Ziehl-Neelson (ZN) staining and Nitrate reductase assay. LPA was performed as per the directions of the manufacturer. McNemar χ2 test was used for statistical hypothesis testing and data was analysed using OpenEpi version 3.
Results: Of the 252 smear positive sputum samples, growth on LJ was seen in 238 (94.4%) samples whereas LPA was positive for 241 (95.6%) samples. Of the 100 smear negative samples growth of MTB was seen in seven samples whereas five were positive by LPA. Sensitivity, specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) for smear positive and negative samples was 100%, 78.6%, 98.9%, 100% and 71.4%, 100%, 100%, 97.9%, respectively. Diagnostic accuracy of the test was 98.6%. One sample showed low level Isoniazid (INH) mono-resistance whereas two samples were hetero-resistant to INH that corresponded to C15T mutation. One sample was resistant to Rifampicin (RIF) that represents a mutation in 531 codon of rpoB gene. Average detection time of MTB on LJ medium was 31.5 days whereas for LPA it was 3.8 days.
Conclusion: LPA due to its rapid turnaround time and high sensitivity and specificity for the detection and susceptibility testing of MTB directly from smear-positive sputum samples can significantly aid in the diagnosis, treatment, and management of MDR-TB. However, LPA cannot completely replace phenotypic culture methods, as the performance of this test is still low for sputum smear negative cases.