International patterns of tuberculosis and the prevalence of symptoms of asthma, rhinitis, and eczema

Background-An ecological analysis was conducted of the relationship between tuberculosis notification rates and the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema in 85 centres from 23 count ries in which standardised data are available. These essentially comprised countries in Europe as well as the USA, Canada, Australia, and New Zealand. Methods-Tuberculosis notification rates were obtained from the World Health Organization. Data on the prevalence of symptoms of asthma, rhinitis, and eczema in 235 477 children aged 13-14 years were based on the responses to the written and video questionnaires from the International Study of Asthma and Allergies in Childhood (ISAAC). The analysis was adjusted for gross na tional product (GNP) as an estimate of the level of affluence. Results-Tuberculosis notification rates were significantly inversely associ ated with the lifetime prevalence of wheeze and asthma and the 12 month per iod prevalence of wheeze at rest as assessed by the video questionnaire. An increase in the tuberculosis notification rates of 25 per 100 000 was asso ciated with an absolute decrease in the prevalence of wheeze ever of 4.7%. Symptoms of allergic rhinoconjunctivitis in the past 12 months were inverse ly associated with tuberculosis notification rates, but there were no other significant associations with other ISAAC questions on allergic rhinoconju nctivitis or atopic eczema. Conclusions-These findings are consistent with recent experimental evidence which suggests that exposure to Mycobacterium tuberculosis may reduce the risk of developing asthma.