Background: The prevalence of asthma appears to be on the increase, and risk factors are not well established. To investigate risk factors for the development of asthma, a population sample of children and adolescents, aged 7-17 years at enrolment, were studied in 1986. Initial examinations were repeated at follow-up in 1992; complete data was available for 408 subjects (199 males).
Methods: Obtained case histories were used to assess the presence of asthma; pulmonary function, skin prick test reactivity, total serum IgE and bronchial responsiveness to inhaled histamine were measured using standard techniques.
Results: The 12-month period prevalence of asthma increased significantly from the first to the second examination in both males (P < 0.001) and females (P < 0.001), whereas the number of subjects with a positive histamine challenge test declined in both sexes, although this was only statistically significant in males (P < 0.001). The prevalence of a positive skin prick test was higher at the second examination (26% and 44%, respectively, P < 0.001); the proportion of subjects with a positive skin reaction to house dust mite (HDM pos) increased from 14% to 26%. Bronchial hyper-responsiveness to inhaled histamine (BHR), HDM allergy, a history of wheezy bronchitis and symptoms of asthma at first examination were more prevalent among subjects reporting asthma at the second examination than among subjects without respiratory symptoms. Confining the analysis to subjects without a history of asthma at the first examination showed that asymptomatic BHR ¿Odds ratio [OR] 3.8 [95% confidence interval (CI) 2.5-5.1], P = 0.0002¿, HDM pos [OR 2.6 (95% CI 1.9-3.3), P = 0.005], a history of wheezy bronchitis before the age of 2 years [OR 3.8 (95% CI 2.4-5.2), P = 0.006] and a history of rhinitis and/or eczema [OR 2.8 (95% CI 1.7-3.9), P = 0.007] at first examination were associated with an increased risk for development of symptomatic asthma at some point between the two examinations. No significant relationship could be demonstrated between smoking (passive or active) and the risk for development of asthmatic symptoms.
Conclusions: In conclusion, this longitudinal population study showed an increase in the 12-month period prevalence of asthma with sensitization to HDM and asymptomatic BHR as important risk factors for development of asthma; the temporal relationship between sensitization to HDM and presence of airway abnormalities needs to be explored further.