Childhood TB: epidemiology reveals two risk periods

The risk of developing TB disease varies widely even within the under-five age group

November 13, 2013 08:50 pm | Updated November 17, 2021 02:56 am IST

This 2006 image provided by the Janice Carr of the CDC shows the Mycobacterium tuberculosis (TB) bacteria in a high magnification scanning electron micrograph (SEM) image.

This 2006 image provided by the Janice Carr of the CDC shows the Mycobacterium tuberculosis (TB) bacteria in a high magnification scanning electron micrograph (SEM) image.

A body of evidence clearly points out that children aged under five years are at-risk group for getting infected with TB and developing disease very soon after infection. And the severe forms of the disease — disseminated TB and meningitis — afflict the young ones.

But apparently, the risk of developing the disease varies widely within the under-five age bracket. According to a 2006 paper in the American Journal of Respiratory and Critical Care Medicine, young children aged under one year run the greatest risk — 30 to 40 per cent risk of progressing to a diseased state, and 10 to 20 per cent risk of suffering from the severe form of the disease (meningitis). In the absence of timely and proper treatment, a majority of these children would die.

>Podcast: TB disease risk variation within the under-five age bracket

The risk drops in those aged one year to two years — 10 to 20 per cent have the risk of progressive from TB infection to disease. The chances of suffering from the severe forms of the disease also plummet to two to five per cent.

There is just five per cent risk of developing disease and 0.5 per cent chance of suffering from disseminated disease in those aged two-five years.

“Features of disease will be found in the great majority of infected children aged less than one year. The disease can be destructive and, if untreated or not prevented, will be responsible for considerable morbidity and mortality,” said Prof. Peter R. Donald. “The features of disease will be found in the great majority of infected young children shortly after infection.” Dr. Donald, Emeritus Professor in the Department of Paediatrics and Child Health, Stellenbosch University, South Africa said at the 44th Union World Conference on Lung Health in Paris.

To drive home the message, Prof. Donald said that during the time when medicines to treat tuberculosis were not available, the mortality percentage was at about 55 per cent in children less than one year but dropped sharply at two years of age and beyond. “During childhood there is a spectrum of disease with a gradient of morbidity and mortality decreasing from infancy to 3-5 years of age,” he said.

“By whatever means the burden of tuberculosis is quantified, the very young have an inordinately high morbidity and mortality,” he added.

The 2006 paper, where Prof. Donald is one of authors, notes: “Among children aged 1-4 years, considerable mortality and morbidity are still encountered before children enter the so-called “safe school age” of 5-10 years.

Interestingly, during childhood (aged under 15 years) a second peak in incidence and mortality is seen when children enter adolescence. He backed his observation with the results of several studies to show the second peaking.

“During adolescence, the risk of disease after infection will vary from 5 to 10 per cent. The risk rises from the age of about 10 years onwards. The nature of the disease also changes and it now becomes typical of adult tuberculosis with cavitation in the upper lobes,” Prof Donald siad.

Large numbers of bacilli are found in the sputum of these diseased children, and they can infect others, as is the case with most adults with disease.

“The reasons for this change of the nature of the disease in adolescence are not well understood, but are probably related to the hormonal changes during adolescence as more females than males are affected,” he explained.

But the disturbing observation is that in developing countries, the shape of the population pyramid is like a Christmas tree, he said. Children under the age of 15 years make up for 40 per cent to 50 per cent in certain communities, notes a 2004 Editorial by Prof. Donald in the International Journal of Tuberculosis and Lung Disease.

This puts the children in the developing countries where TB is widely prevalent, especially India, which has the highest global TB burden, at particularly high risk of TB infection and disease.

In the high-burden communities, children may comprise 20 per cent or more of the [total] TB caseload, the Editorial notes.

In sum, his message at the conference was that “in tuberculosis, the incidence, particularly of active cases, among children is a prime index of the prevalence of tuberculosis in the community,” as a 1952 paper had noted.

( The Correspondent participated in the 44th Union World Conference on Lung Health in Paris at the invitation of the Global Health Strategies, New Delhi. He is a recipient of the 2013 REACH Lilly MDR-TB Partnership National Media Fellowship for Reporting on TB. )

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