Culture conversion at 2 months among patients with rifampicin-susceptible pulmonary tuberculosis: a prospective cohort study

Abstract

<b>Introduction:</b> Compared to drug-susceptible tuberculosis (DS-TB), isoniazid-monoresistant resistant TB (Hr-TB) is associated with unfavorable outcomes. However, roles of mutations associated isoniazid (INH) resistance is not well investigated. <b>Aims:</b> Our objective is to identify impact of genetic mutations of INH resistance on 2-month culture conversion among Hr-TB patients. <b>Methods:</b> We conducted a prospective cohort study at 3 university-affiliated hospitals in the Republic of Korea between 2017 and 2020 and enrolled pulmonary TB patients who had line probe assay. Culture-negative and rifampicin-resistant TB were excluded. Hr-TB and DS-TB were defined based on results of phenotypic drug susceptibility test (pDST). We conducted a multivariable logistic regression analysis to assess association between 2-month culture conversion and katG mutation. <b>Results:</b> Of 300 enrolled patients with culture-positive rifampicin susceptible pulmonary TB, 19 (6.3%), 13 (4.3%), and 11 (3.7%) had Hr-TB, katG mutation, and inhA mutation, respectively. Percentage of positive culture result at 2 months was 7.0%. Compared to DS-TB, Hr-TB was significantly associated with 2-month positive culture result (adjusted odds ratio [aOR], 4.05; 95% confidence interval [CI], 1.06-15.51). Those with katG mutation was also associated with 2-month positive culture result (aOR, 4.99; 95% CI, 1.13-21.99). <b>Conclusions:</b> Similar to INH-resistance on pDST, katG mutation could predict 2-month culture conversion. Prompt changes of treatment regimens based on line probe assay would be beneficial among Hr-TB patients.