A new quantitative method to estimate annual incidence of tuberculosis (TB) in India by the Ministry of Health and Family Welfare has depicted a clear urban rural divide for the infectious disease.
The method revealed that while TB case infects more individuals per year in urban centres, rural TB case remains infectious for longer strongly suggesting the need for interventions tailored to different settings.
"There are differences in urban and rural TB dynamics, specifically the number of people likely to be infected by a single patient and the length of time that patient remains infectious, both of which affect strategies for control.
An urban TB case will infect an average of 12 people per year and remains infectious for about one year, while a rural case will infect an average of four people per year, but remains infectious for more than two years," the report based on the new model said.
The Epidemiology and Research Division at National Tuberculosis Institute under Union Health Ministry partnered with Center for Disease Dynamics, Economics and Policy (CDDEP), Public Health Foundation of India, Princeton Environmental Institute, USA, and the Department of Infectious Disease Epidemiology, Imperial College London to develop the method based on mathematical modelling to estimate annual incidence of TB. The methodology report was also published in International Journal of Tuberculosis and Lung Disease on Wednesday.
When applied to India, the model suggested an annual incidence of smear-positive TB (the most infectious and most likely to transmit their disease in their surroundings) of 89.8 per 1,00,000 people.
India bears the highest burden of TB globally with about 25 per cent of all cases. The extent of TB in high-burden and low-resource regions is difficult to measure directly, but knowing the number of cases is necessary to plan, staff and finance control programs, the officials said.
"We urgently need improved estimations of the burden of tuberculosis. To implement appropriate policies and interventions, it is important to understand the current extent of the disease, as well as transmission dynamics," CDDEP Director Ramanan Laxminarayan, said.
"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," he said.
The model suggested the TB incidence (all forms of TB including pulmonary and extrapulmonary including organs other than lungs) of 141.9 individuals per 1,00,000 people in India.
According to Indian Council of Medical Research, the average prevalence of all forms of tuberculosis in India is estimated to be 5.05 per thousand, prevalence of smear-positive cases 2.27 per thousand and average annual incidence of smear-positive cases at 84 per 1,00,000 annually. It is estimated to kill 4,80,000 Indians every year although it is now believed that these numbers are underrepresented and that the mortality could be around 5,00,000 a year.
While India has been engaged in tuberculosis control efforts for decades now, TB continues to remain one of its biggest public health challenges. As India aims to eliminate TB by 2025, the Union Health Ministry has made it mandatory for hospitals and clinics to notify all TB cases.
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