Contact screening: the risk of wrong TB diagnosis

October 24, 2013 02:48 am | Updated November 16, 2021 08:11 pm 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.

Of the nine million cases of tuberculosis (TB) across the world annually, children below 15 years of age account for about one million. As per India’s Revised National TB Control Programme (RNTCP), paediatric cases account for about 12 per cent of the total TB caseload in the country.

According to a March 2013 paper in the Indian Pediatrics journal, the number of paediatric (below 14 years) cases in India has been on the rise — nearly 60,000 (5.6 per cent) in 2005 and about 84,000 (7 per cent) in 2011. Many studies have pointed out that paediatric TB case detection is way down in the priority list of RNTCP and hence many cases go undetected.

Of the paediatric cases, children under five years are particularly vulnerable to getting infected and developing active TB. This is all the more true in the case of children from households where an adult has been recently diagnosed with sputum smear positive active pulmonary TB.

Several studies have shown that there is greater prevalence of TB infection and disease in these children than in those from households were all adults are healthy. The risk of children getting infected and diseased depends on proximity and duration of contact, and the severity of disease in the adult (index case).

Besides having a greater risk of getting infected/diseased, children under five from such households have heightened risk of developing severe forms of the disease — disseminated TB and meningitis. If the progression from infected to diseased state takes about two years in children below five years, it is 6-8 weeks in the case of infants.

It is for these reasons that both the WHO and RNTCP have recommended contact screening of children under five years followed by isoniazid prophylactic therapy for six months for the infected, asymptomatic children and a multi-drug regimen for the diseased.

But diagnosing children with active TB with a great degree of confidence is the biggest challenge. That’s because young children are unable to produce sputum. And even if they do produce or if sputum is obtained invasively, the sputum contains only a few TB bacteria. Hence, many active TB cases end up being sputum smear negative. Other diagnostic tools have their own limitations and challenges.

But is there anything specific with TB in a young child that makes diagnosis using all available tools, sputum sample and clinical symptoms so very difficult? “It sometimes is difficult to differentiate infection from disease as it may be a continuum (not always),” Dr. Varinder Singh, Professor, Department of Pediatrics, Lady Hardinge Medical College and Assoc Kalawati Saran Children's Hospital, New Delhi stated in an email to this Correspondent.

Yet, as the updated national guidelines for paediatric TB in India point out, utmost care needs to be taken to ensure that children with active TB are not wrongly diagnosed as infected, asymptomatic, disease-free cases and given isoniazid preventive therapy.


The reasons are quite obvious. Any wrong diagnosis and late detection of disease in those undergoing prophylactic monotherapy can lead to grave consequences.

“Incorrect diagnosis could delay treatment, and since younger children rapidly develop serious forms of disease, such errors can increase their morbidities,” Dr. Singh emphasised.

“Children will not respond to treatment and will continue to have symptoms. It all depends on the size of the lesion in the lungs,” said Dr. Soumya Swaminathan, Director of the Chennai-based National Institute for Research in Tuberculosis (formerly Tuberculosis Research Centre).

Considering the challenge in diagnosing TB and the fact that many diseased children end up getting wrongly administered with the isoniazid prophylactic drug, the need to be checked by a doctor at regular intervals cannot be overemphasised.

“A check should be kept for any occurrence of clinical symptoms. Parents must be asked to bring patients for a check-up in case of any ill health or deviation from the normal pattern of growth.

“Our practice is to see them every four weeks in addition to as needed basis,” Dr. Singh explained. “They should also be checked for side-effects caused by the drug and to make sure there is no active TB,” Dr. Swaminathan noted.

But sadly, with even contact screening of young children not given priority in the RNTCP programme, the question of regular follow-up of those on prophylactic therapy does not even arise.

Drug resistance

Fortunately, owing to the few TB bacilli in children, the risk of drug resistance due to intermittent or irregular intake or discontinuation of the drug during the six-month isoniazid regimen is low unlike in the case of adult TB patients. “It would be very rare to develop drug resistance in a situation where bacilli are few,” Dr. Swaminathan said.

Dr. Singh added:“Most of the clinical resistance is due to selection of pre-existing resistant mutants and since the frequency of resistance is very low — 1 in 100,000 or more, the probability of drug resistance in a child with fewer TB bacilli is therefore also less.” Isoniazid resistance in the general adult population is 10-15 per cent.

( The Correspondent is a recipient of the 2013 REACH Lilly MDR-TB Partnership National Media Fellowship for Reporting on TB .)

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