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Editor,—There is no doubt that BCG increases sensitivity to tuberculin but this cannot be taken to equate with protection against tuberculosis as is implied by a number of studies including 2 cited in the article by Bannon.1 Evidence from the large Medical Research Council (MRC) trial in the UK showed that after BCG vaccination, non-responders to a 3 tuberculin unit (TU) Mantoux test had the same degree of protection against tuberculosis as responders.2 The delayed hypersensitivity reaction should not be regarded as evidence of immunity but as evidence of infection. Distinguishing a BCG infection from tuberculosis infection may be difficult and the tuberculin test is only one element in the assessment. In a high risk population in Leicester who had neonatal BCG vaccination, use of a 1 TU Mantoux test (0.1 ml of 1 in 10 000) can significantly and safely reduce the number of children who need chemoprophylaxis.3
The larger tuberculin response that follows later vaccination4 is not evidence that neonatal BCG is less effective. The present system of universal vaccination at 13 years is illogical and derives from the original MRC trial design. This age was chosen for operational and statistical reasons that have nothing to do with the clinical effectiveness of the vaccine.5 A more rational approach would be to dispense with school BCG in favour of universal neonatal BCG, which is logistically much easier and protects those most at risk of the disease (young children) from its most serious manifestations. Funding for tuberculosis services could then be directed more towards case finding and treatment compliance, which will break the transmission of disease to the next generation.
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Dr Bannon comments:
The tuberculin protein skin test should never be used in isolation in the diagnosis of childhood tuberculosis. A more rigorous approach is required that includes good history taking, meticulous clinical examination, and judicious use of appropriate investigations. A positive tuberculin protein skin test merely indicates that a child’s immune system has been exposed to certain strains of mycobacteria. However, there is now some agreement that a reaction is more likely to be indicative of infection rather than prior BCG immunisation if:
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it is strongly positive
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BCG had been given at least five years previously
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there had been close contact with a sputum positive adult
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the child is a recent immigrant form a part of the world where there is a high prevalence of TB.1-1
All children fulfilling these criteria must be referred for specialist opinion.
It would be illogical to discontinue with the school BCG programme at this present time. Even if universal neonatal BCG immunisation were to be implemented immediately, there would still be a large cohort of children who would remain unprotected for many years. School attendance is an ideal opportunity for opportunistic health promotional activities, and tuberculin protein testing of adolescents should continue to detect those children who have subsequently become infected with the Mycobacterium tuberculosis bacillus or who, despite receiving neonatal BCG, have developed active tuberculosis.
For the foreseeable future, we should continue with existing TB prevention and eradication programmes. In addition, TB must achieve a higher profile in medical education programmes and in future strategic health care planning. Incidentally, how many readers were aware that 24 March 1999 was world TB awareness day?
References
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