Use of the tuberculin skin test in children.

The tuberculin skin test, originally developed by Koch over a century ago as a means to treat tuberculosis, has emerged as the definitive means to identify infection with Mycobacterium tuberculosis. Its value was first demonstrated in studies of student nurses in Norway where it correctly identified uninfected students at greatest risk of dying of tuberculosis during the course of their training. The test was used to investigate contacts of active cases of tuberculosis, especially children. Cohort studies of such children undertaken in the 1950s and early 1960s showed that those who developed an induration in response to the tuberculin test of 10mm or greater were most likely to go on to develop tuberculosis in the future and that, if they were treated with isoniazid for a prolonged period (with maximal effect after 12 months of treatment), they were substantially less likely to develop tuberculosis. Since that time, the tuberculin skin test has been used extensively to identify individuals who have been infected with Mycobacterium tuberculosis and who would most likely benefit from treatment of latent tuberculous infection. Subsequently, international experts recommend that all children under five years of age who are in contact especially with sputum smear positive cases of tuberculosis should all be tested with tuberculin if it is available. Those found to have a significant reaction should be treated with isoniazid if they do not have active tuberculosis. Moreover, the tuberculin skin test has been used as a reliable means to monitor the progress of tuberculosis in the community through the means of surveys of school children to determine prevalence (and estimate incidence) of tuberculous infection in the community. The tuberculin skin test is not easy to administer or to interpret and requires careful application and interpretation. Tuberculin consists of a mixture of material produced by Mycobacterium tuberculosis as it is growing. It is prepared in a form termed 'purified protein derivative (PPD)' but is neither pure nor consists entirely of protein. Reference material has been developed to standardise it. The reading of the result of tuberculin testing requires experience and care. Inexperience leads to error (terminal digit preference). Tuberculin also detects the presence of antigens from other Mycobacteria species the most important of which is environmental Mycobacteria. Previous vaccination with BCG has less effect on the results of the test. The tuberculin test is useful to detect infection in children.