What proportion of new tuberculosis patients has a history of household tuberculosis exposure? A cross-sectional study from Udupi district, South India

While tuberculosis (TB) preventive therapy among household contacts is effective at an individual level, its population-level impact on reducing TB incidence has been unclear. In this study, we aimed to assess, among the new tuberculosis patients started on treatment between 1 October, 2018 and 30 June, 2019 in the public health facilities of Udupi district (South India): i) the proportion with a 'history of household TB exposure' and ii) sociodemographic and clinical factors associated with it. We conducted a cross-sectional study involving record review and patient interviews. Of 565 TB patients, 273(48%) were interviewed. Of them, 71(26%, 95% CI: 21%-32%) patients had a 'history of household TB exposure (ever)' with about half exposed in the past five years of diagnosis. Considering a new TB case as a proxy for incident TB, and 'history of household TB exposure' a proxy for household transmission, and assuming 100% effectiveness of preventive therapy, we may infer that a maximum of 26% of the incident cases can be prevented by giving preventive therapy to all household contacts of TB patients. In multivariable analysis, females and tobacco users had a significantly higher prevalence of household TB exposure. If there are resource constraints, these subgroups may be prioritized.