BCG, tuberculin skin-test results and asthma prevalence in school children in North London.

Objective: To test whether there is any relationship between asthma prevalence and BCG immunization or tuberculin skin test reaction. Design: Cross-sectional survey. Setting: Secondary school in Haringey, North London, UK. Subjects: 780 children aged 11-18 years (median 13.35 years). Interventions: Administration of tuberculin skin test and questionnaire. Main outcome measures: Diagnosis of asthma, presence of nocturnal cough, exercise-induced wheeze or wheeze with viral respiratory infections; diameter of induration with tuberculin skin test; history of BCG immunization. Results: 57 of 629 children (8.5%) had a significantly positive Mantoux reaction(≥15 millimeters of induration). Children with and without a history of BCG immunization did not differ significantly in prevalence of asthma diagnosis (11.8% vs 14.1%, p >0.6), exercise-induced wheeze (16.9% vs 21.2%, p >0.4), viral-induced wheeze (15.4% vs 7%, p >0.6) or nocturnal cough (32.3% vs 32.7%, p >0.6). We also found no significant correlation of the prevalence of asthma diagnosis or symptoms with diameter of Mantoux test reaction. Conclusions: There is no evidence of an effect of BCG immunization or tuberculin reactivity on the incidence of asthma in secondary school children in Haringey, North London and the exposure to tuberculosis is high in these children.