Prueba de la tuberculina y riesgo de tuberculosis. No sólo el tamaño es importante / The tuberculin skin test and risk of tuberculosis: size is not the only issue

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[Non-specific tuberculin reactivity due to sensitization to non-tuberculous mycobacteria (NTM) in children not vaccinated with BCG. Diagnostic value of a comparison of intradermal tests with tuberculin and NTM antigens]. / Réactivité tuberculinique non spécifique par sensibilisation aux mycobactéries non tuberculeuses (MNT) chez des enfants non vaccinés par le BCG. Intérêt diagnostique de la comparaison des tests intradermiques à la tuberculine et aux antigènes de MNT.

Sensitisation to non tuberculous mycobacteria (NTM) may provoke a non specific tuberculin reaction and can cause problems in the interpretation of tuberculin tests in subjects who have not been vaccinated with BCG. The practice of testing for antigens to NTM (sensitins) should be useful for pointing to the right diagnosis. Our study was carried out on 24 asymptomatic children aged between 11 months and 8 years 9 months; these children were considered to be sensitive to NTM based on comparative cutaneous tests (reactions to sensitins > or = 5 mm and > or = 3 mm vs tuberculin) and were selected from a group of 53 children who had either initially achieved a positive tuberculin reaction or who had undergone conversion on subsequent prevaccination testing. The tests were carried out with tuberculin RT 23, tuberculin Merieux and sensitins from M. avium and M. intracellulare. They had been repeated two to four months later in cases of a response to one of the different reactants. At the first examination the tuberculin reactions were most often weak, the Merieux tuberculin induced a stronger response than the RT23 tuberculin. A dominant response for one or both sensitins was present in 18 cases. The tuberculin reactions became weaker whilst the sensitins remained relatively stable. The difference became significant in the six remaining cases. Although tests for tuberculin and sensitins have some diagnostic value which is necessarily imprecise, comparative analysis of the cutaneous reactions to the different antigens may contribute to avoid an erroneous interpretation for tuberculin allergy in asymptomatic young children without any risk factors for tuberculous infection. It is important to identify those subjects having non specific tuberculin reactivity induced by sensitisation to NTM in order to avoid non justified chemoprophylaxis and also to be able to vaccinate these children with BCG.