Abstract
SUMMARYBACKGROUND: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.RESULTS: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.CONCLUSIONS:Simple models of TB transmission, in conjunction with necessary data, can offer approaches to burden estimation that complement those currently being used.
Highlights
TUBERCULOSIS (TB) is a major global public health challenge
In the model the population is divided into different categories: uninfected (U), latent infection (L), active disease and cured (R). Population flows between these states are represented by the following system of ordinary differential equations that capture TB transmission dynamics as well as other factors, including breakdown to active disease, mortality, cure and relapse
We describe the sources of these parameters: first, ARTI is a measure of the force of infection, defined as the probability of acquiring new tuberculous infection or re-infection over a period of 1 year, and is derived mathematically from the prevalence of infection estimated by tuberculin surveys
Summary
TUBERCULOSIS (TB) is a major global public health challenge. Of the estimated 10.4 million cases globally in 2015, only about three fifths were notified to the public health authorities.[1] The ‘missing cases’ pose a serious challenge to TB control. To design appropriate case-finding interventions and gauge the efficiency of the public health system in capturing TB cases, it is imperative to have more precise estimates of TB incidence, especially in high-burden countries such as India.[2] in any given national setting, estimating annual TB incidence is challenging. The direct measurement of active TB incidence requires large study populations to be followed for a year or longer, while carefully accounting for TB cases entering or leaving the population during this time. The resources, personnel and funding needed to sustain this effort in high-burden, low-income countries render such direct measurements impractical.[3]
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