A new study quantifying the global burden of Tuberculosis (TB) 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 Monday 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.

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.

Dr Michel Gasana, the head of TB division at Rwanda Biomedical Centre, did not rule out the possibility of misdiagnosing .

"One of the commonest methods for diagnosing T.B is through screening the mucous membrane of saliva, so a three-year-old child may be too immature to produce this kind of substance,” he said. "Most of the microscopes we have are the old fashioned kind that have comparatively low sensitivity, thereby increasing chances of misdetection.”

He added that the country has few radiologists, about five or six, and most of them are concentrated around Kigali, reducing chances of diagnosing the disease through X-ray or C.T scan.

Dr Daniel Nyamwasa, an infectious diseases specialist at Kacyiru Police Hospital, said it is important not to only rely on one screening method like microscopes but also consider others like X-ray, and the scan system to be sure.

"The TB may not show when you screen the saliva membrane, but it may do, for instance, if you carry out a chest x-ray,” he observed.

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 Organisation (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, experts say.

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 it deserves. 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.

Alpha Uwimana, an infectious diseases specialist working with Pharma clinic in Gikondo, a Kigali suburb, said diagnosing TB is sometimes difficult as it sometimes has similar symptoms like bronchitis and pneumonia.

Gasana, however, said government had come up with various measures aimed at reducing TB mis-diagnosis, for instance in the last two years, about 16 GeneXpert (highly sensitive TB detection) machines were procured and that plans are underway to procure one for every district hospital in the next three years .

"The good news is that unlike before, the World Health Organisation has now approved the use of the GenXpert machine even on children, so cases of mis-detection will greatly reduce.”

He added that they are planning to use a digital network system, that can, for instance, help a doctor and laboratory technician share an x-ray report of a particular patient quickly, helping with interpretation and advising where necessary, regardless of distance.

Gasana said the country have also acquired about 50 Fluorescence microscopes, which have a 10 per cent higher sensitivity than ordinary ones, and that they are hoping to acquire 200 others over the next three years.

In Rwanda, TB cases registered have been reducing over the years, from 8000 in 2006 down to 6000 in 2013 according to RBC figures.