Burden of Isoniazid Monoresistant Tuberculosis in Sputum Sample of Patients Attending a Tertiary Care Center, Trichy, India

In drug resistant tuberculosis (DRTB), Rifampicin resistance has always been prioritized hence Cartridge Based Nucleic Acid Amplification Test (CBNAAT) is recommended. However, since it doesn’t detect isoniazid resistance, rifampicin sensitive patients with unknown isoniazid status may be erroneously treated as drug sensitive TB leading to poor treatment outcomes and emergence of multidrug resistant (MDR) TB. Hence this study was undertaken to estimate the prevalence of isoniazid monoresistant TB and to find out the level of isoniazid resistance using Line probe assay (LPA). A total of 3227 consecutive sputum samples of patients between July 2023 and December 2023 were enrolled for the study. The samples were subjected to smear microscopy, CBNAAT and LPA (Line Probe Assay) and the results were documented. In our study the prevalence of isoniazid monoresistance was estimated to be 8.2%. Among isoniazid monoresistance the prevalence of high level resistance was 65.7% and that of low level resistance was 31.5%. This shows that isoniazid monoresistance forms a major chunk of DRTB, with majority of patients having high level resistance to isoniazid. Thus, LPA serves as a rapid diagnostic tool especially for the detection of isoniazid monoresistance.