ObjectivesIn high TB burden countries like Bangladesh, research and policies tend to focus on rifampicin (RIF)-resistant TB patients, leaving RIF sensitive but isoniazid (INH) resistant (Hr-TB) patients undiagnosed. Our study aims to determine the prevalence of INH resistance among pulmonary TB (PTB) patients in selected healthcare facilities in Bangladesh. MethodsThis study was conducted across nine TB Screening and Treatment Centers situated in Bangladesh. Sputum samples from 1084 Xpert-positive PTB patients were collected between April 2021 and December 2022, and cultured for drug susceptibility testing (DST). Demographic and clinical characteristics of Hr-TB and drug-susceptible TB patients were compared. ResultsAmong available DST results of 998 culture positive isolates, resistance rate of any INH regardless of RIF susceptibility was 6.4% (64/998, 95% CI, 4.9-8.2). The rate was significantly higher in previously treated (21.1%, 16/76, 95% CI, 12.0-34.2) compared to newly diagnosed TB patients (5.2%, 48/922, 95% CI, 3.8-6.9) (p <0.001). The rate of Hr-TB was 4.5% (45/998, 95% CI, 3.3-6.0), which was also higher among previously treated (6.6%, 5/76, 95% CI, 1.4-13.5) compared to newly diagnosed TB patients (4.3%; 40/922, 95% CI, 3.1-5.9) (p=0.350). Most importantly, the rate of Hr-TB was more than double compared to MDR-TB (4.5%, 45/998, vs 1.9%, 19/998) found in the current study. ConclusionsThis study reveals a high prevalence of Hr-TB, surpassing even that of the MDR-TB in Bangladesh. This emphasizes the urgent need to adopt WHO-recommended molecular tools at the national level for rapid detection of INH resistance so that patients receive timely and appropriate treatment.