Estimating tuberculosis incidence from primary survey data: A mathematical modeling approach

BACKGROUND: There is an urgent need for improved estimations of the burden of tuberculosis (TB). OBJECTIVE : To develop a new quantitative method based on mathematical modelling, and to demonstrate its application to TB in India. DESIGN: We developed a simple model of TB transmission dynamics to estimate the annual incidence of TB disease from the annual risk of tuberculous infection and prevalence of smear-positive TB. We first compared model estimates for annual infections per smear-positive TB case using previous empirical estimates from China, Korea and the Philippines.We then applied the model to estimate TB incidence in India, stratified by urban and rural settings. RESULT S : Study model estimates show agreement with previous empirical estimates. Applied to India, the model suggests an annual incidence of smear-positive TB of 89.8 per 100 000 population (95%CI 56.8- 156.3). Results show differences in urban and rural TB: while an urban TB case infects more individuals per year, a rural TB case remains infectious for appreciably longer, suggesting the need for interventions tailored to these different settings. CONCLUS IONS : Simple models of TB transmission, in conjunction with necessary data, can offer approaches to burden estimation that complement those currently being used.