Five-year incidence rate of tuberculosis disease among household contacts of extrapulmonary tuberculosis patients in South-west Karnataka - A retrospective cohort study

Background National Tuberculosis Elimination Programme focuses more on open (pulmonary) cases of tuberculosis. In addition to pulmonary tuberculosis, extrapulmonary tuberculosis cases also contribute to the tuberculosis burden and spread of infection among household contacts. This study aims to estimate the incidence of tuberculosis disease among household contacts of extrapulmonary tuberculosis cases and to describe the associated risk factors. Methods This retrospective cohort study was done in Mandya, Ramanagar, Mysuru, and Chamarajanagar districts of South-west Karnataka covering household contacts of 1428 extrapulmonary tuberculosis cases registered in the study districts between 2017 and 2018. Data was collected by telephonic interviews from 4705 household contacts. Descriptive statistics, inferential statistics and Kaplan-Meier survival analysis were used. Results Among 4705 household contacts, 48(1%) study participants had developed active tuberculosis. Of them, 35(73%) had pulmonary tuberculosis and 13(27%) had extra pulmonary tuberculosis. Among the newly diagnosed, 31(65%) were males and 17(35%) were females. Risk factors like diabetes and alcohol intake were found to be associated with increased tuberculosis incidence in household contacts of extrapulmonary tuberculosis. Maximum TB incidence occurred during the first 12 months i.e., 24(50%). 39 out of 48 cases did not have any other known case of tuberculosis as common contact. Conclusions Five-year incidence of tuberculosis among household contacts of extrapulmonary tuberculosis cases was 1% and diabetes mellitus, alcohol intake were main risk factors for tuberculosis incidence.