A new study quantifying the global burden of tuberculosis among children suggests there are tens of millions of children with undiagnosed TB.

Researchers at the University of Sheffield, Imperial College London, and TB Alliance found evidence that there is a large gap between the number of recorded TB cases and the true incidence. The study, published today in Lancet Global Health, shows that TB in children is a major public health problem worldwide.

The investigators estimated the number of children with TB in the 22 countries with the highest burden of TB in the world using a mechanistic mathematical model. In contrast with standard estimates that are reliant on paediatric case reporting, which varies widely between countries, the researchers took a complementary approach, using mathematical modelling to estimate rates of infection and disease in children based on country-specific data on household and population structure, and the prevalence of TB in adults. The model incorporated both social and epidemiological variables including the effects of age, BCG vaccination efficacy, and the effect of HIV infection.

The study suggests that in these 22 countries more than 650,000 children developed the disease in 2010, while 7.6 million became infected with the TB bacterium. Overall more than 53 million children were estimated to harbour a latent infection.

Diagnosing TB in children can be challenging and the disease can often be overlooked or mistaken for something else. This can lead to under-reporting, distorting the true scope of the problem and the real demand for paediatric TB treatment.  

The first estimates of paediatric TB by the World Health Organization (WHO) were published in 2012, and last year the WHO estimated 530,000 paediatric cases worldwide. However, given the acknowledged difficulties in detecting TB in children, there is need for additional research and focus on the burden of disease in children.

Health economics researcher Peter Dodd, from the University of Sheffield’s School of Health and Related Research (ScHARR), said: “Quantifying the burden of TB in children is important because, without good numbers, there can be no targets for improvement, no monitoring of trends and there is a lack of evidence to encourage industry to invest in developing medicines or diagnostics that are more appropriate for children than those available today.”

He added: “Historically, TB in children has not received the attention that it might have done. The WHO is now encouraging countries to report the number of TB cases they find in children, but we still have only a poor idea what proportion of cases are recorded in youngsters.”

The 22 countries with high TB investigated in the study are reported to harbour 80 per cent of the global burden. In addition to providing global estimates, the study also suggests that over a quarter of all paediatric TB cases were in India and 15 million children under the age of 15 were living with somebody who had TB. The 53 million children with latent TB represent a huge reservoir for future disease.

Co-author of the study, Dr James Seddon from the Department of Medicine, Imperial College London, said: “Although these 53 million infected children may not be currently experiencing any problems, they are at a very high risk of developing the disease in the future. It is also interesting to note that only a third of children with TB disease are currently identified, treated and reported. This compares to two thirds in adults.”

The study is part of a larger effort, led by TB Alliance and supported by UNITAID and USAID, to improve TB treatment for children and deliver optimised child-friendly first-line TB drugs. 

Reference: Dodd et al. ‘Burden of childhood tuberculosis in 22 high-burden countries: a mathematical modelling study’ 2014 Lancet Global Health http://www.thelancet.com/journals/langlo/article/PIIS2214-109X(14)70245-1/abstract