An investigation of the impact of index case screening on commonly reported epidemiological estimates in tuberculosis (TB) household contact study

Tuberculosis, a chronic infectious disease caused by Mycobacterium tuberculosis (Mtb), remains as one of the biggest threats to public health worldwide. The purpose of this study is to investigate the impact of different screening criteria of the index cases on epidemiological estimates in the tuberculosis (TB) household contact study. Six different screening criteria were designed based on whether the index cases were adults and lived in the crowded environment, as well as their sputum smear and culture test results. Logistic regression was performed to determine the risk factors of TB. We found that gender, HIV-infection, smoking, malnutrition and diabetes were associated with Mtb infection. We also found significant differences of epidemiological estimates among observation groups screened by different criteria. The number of infections were relatively higher in the studies where index cases were screened as positive sputum smear and living in the crowded environment, indicating that index cases with positive sputum smear and live with more than two contacts in one room were likely to be more infectious in the household. Therefore, it is suggested that screening and treatment should be strengthened for those designs so that transmission of Mtb infection in the household can be reduced.