Rapid and Economical Detection of Multidrug Resistant (MDR) Tuberculosis: Can Rifampicin Resistance (RMPr) be a Surrogate Marker for MDR-TB ?
Successful treatment of multidrug resistant tuberculosis (MDR-TB) relies on prompt laboratory detection of drug resistance. The study was aimed to investigate utility of GenoType MTBDRplus (Line probe assay: Genotypic) as rapid method for MDR-TB detection and for rapid economical detection of MDR-TB, Direct Sensitivity Test (Phenotypic-Direct) was evaluated. Further an attempt also made to investigate the importance of Rifampicin resistance (RMPr) as a surrogate marker for multidrug resistance (MDR) tuberculosis. Forty-three sputum (acid fast bacilli smear positive =1+ & above) specimens constituted the material for this study. RMPr /MDR detection was done by Line Probe Assay(LPA) and Direct Sensitivity(DS), which was further evaluated with Proportion method (PM: phenotypic) which was considered as gold standard for statistical calculations. LPA as well as DS was found to be 100% sensitive for detection for MDR. LPA results analysis further revealed S531L (rpoB) + S315T1 (kat G) to be the commonest mutation pattern. The present study found RMPr to be a good surrogate marker for identifying MDR strains. However, our retrospective analysis of 5-years published data based on proportion method showed the percentage of MDR would increase from 47.54% to 74.44% if we consider rifampicin monoresistance as surrogate marker for MDR.This study found that the LPA is good rapid technique which can be used for rapid detection of MDR/RMPr. Direct Sensitivity is another suitable option for resource constraint settings. Both the techniques were well comparable with the gold standard proportion method. Larger studies are required to call RMPr as surrogate marker of MDR-TB. LPA is definitely a good tool for rapid detection of MDR provided one has a requisite infrastructure and trained man-power. The results of DS test were really encouraging which made us to think to replace proportion method where a lot of technical expertise required. Larger studies are required to call RMPr as surrogate marker of MDR-TB.
Priyanka Kembhavi, Sarala Menon, Nilma Hirani, Vaishali Wabale and Ameeta Joshi