Role of line probe assay in detection of extra-pulmonary tuberculosis: Experience from a tertiary care hospital in western Maharashtra

Abstract

BackgroundDiagnosis of extra pulmonary tuberculosis (EPTB) is challenging due to its atypical clinical presentation and frequently results in a delay or deprivation of treatment. Apart from rapid case detection, early determination of MDR status is imperative in such situations. The commercially available Geno Type MTBDRplus assay version 2.0 (Hain Lifescience, Nehren, Germany) detects both the presence of Mycobacterium tuberculosis (MTB) complex as well as the presence of INH and Rifampcin resistance. We aim to evaluate the role of this test in diagnosis and detection of resistance by comparing its performance against gold standard i.e. culture and against the composite reference standards (CRS) in the diagnosis of EPTB. Material and methodsThe data of 130 EPTB samples processed form January 2014 till May 2017 at Poona Hospital and Research centre were selected for the study. All the samples were processed for Ziehl–Neelsen stain, Geno Type MTBDRplus assay (LPA) and liquid automated culture (BacT/Alert) simultaneously. Geno Type MTBDRplus assay (LPA) was performed directly on the samples. The 24 samples giving positive results on LPA and grown M. tuberculosis on culture were subjected to anti mycobacterial susceptibility testing for 1st line anti-tubercular drugs by BACTEC MGIT 320 system. ResultsOut of 130 samples, 7 samples grew atypical mycobacterium and all the 7 samples turned negative on Line Probe Assay. Direct LPA on processed samples yielded 48/130 (36.9%) positivity. Geno Type MTBDRplus assay was positive for M. tuberculosis in (72.09%) 31/43 culture positive cases and (21%) 17/80 of culture negative cases. Geno Type MTBDRplus assay sensitivity and specificity results were assessed in comparison to CRS made up of culture results and clinical, radiological and histological findings. The overall sensitivity of Geno Type MTBDRplus assay was 45.19% (47/104) and specificity was 94.73 (18/19). Out of 24 samples which were compared for results between LPA and culture, Geno Type MTBDRplus assay accurately identified 3 of 3 of Rifampcin resistant strains and 20 of 21 Rifampcin sensitive strains. Geno Type MTBDRplus assay identified 4 of 4 INH resistant strains and 19 of 20 INH sensitive strains and MDR was obtained for 3 of 3 strains. ConclusionsGeno Type MTBDRplus assay can give early diagnosis and sensitivity for both INH and Rifampcin in extra pulmonary samples. More number of studies is further required to establish Geno Type MTBDRplus assay as an important tool for obtaining diagnosis and resistance to first line drugs in extra pulmonary samples.