High frequency of isoniazid and fluroquinolone resistance among patients with rifampicin sensitive tuberculosis

This study was done to determine frequency of isoniazid (INH) and fluoroquinolones FQ resistance among rifampicin sensitive strains of Mycobacterium tuberculosis and to study their mutation patterns. Retrospective analysis was done for samples with M. tuberculosis detected by Cartridge based NAAT (CBNAAT). They were tested sequentially by first line (FL) and second line - line probe assay (SL-LPA) depending on their drug resistance pattern and following diagnostic algorithm. Total 9722 (74.1 %) of 13124 NAAT positive samples were sensitive for rifampicin. On FL-LPA, 833 (8.6 %) were resistant to INH and of which 110 (13.2 %) were also resistant to FQ by SL-LPA. Most common mutations observed for INH resistance were katG S315T1 mutation in 615 (97.3 %) strains, inhA C15T mutation in 174 (86.6 %) strains and for FQ resistance were gyrA D94G mutation in 46 (41.8 %) strains. Heteroresistance, inferred mutations, combination of mutations and unique mutations were also observed in all genes.