RISK-FACTORS FOR DEVELOPMENT OF ASTHMA IN CHILDREN AND ADOLESCENTS - FINDINGS FROM A LONGITUDINAL POPULATION STUDY

Background. The prevalence of asthma appears to be on the increase, an d risk factors are not well established. To investigate risk factors f or the development of asthma, a population sample of children and adol escents, aged 7-17 years at enrolment, were studied in 1986. Initial e xaminations were repeated at follow-up in 1992; complete data was avai lable for 408 subjects (199 males). Methods: Obtained case histories w ere used to assess the presence of asthma; pulmonary function, skin pr ick test reactivity, total serum IgE and bronchial responsiveness to i nhaled 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 statist ically significant in males (P<0 . 001). The prevalence of a positive skin prick test was higher at the second examination (26% and 44%, res pectively, P<0 . 001); the proportion of subjects with a positive skin reaction to house dust mite (HDM pos) increased from 14% to 26%. Bron chial hyper-responsiveness to inhaled histamine (BHR, HDM allergy, a h istory of wheezy bronchitis and symptoms of asthma at first examinatio n were more prevalent among subjects reporting asthma at the second ex amination than among subjects without respiratory symptoms. Confining the analysis to subjects without a history of asthma at the first exam ination showed that asymptomatic BHR {Odds ratio [OR] 3 . 8 [95% confi dence 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 histo ry 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 deve lopment of symptomatic asthma at some point between the two examinatio ns. 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 showe d an increase in the 12-month period prevalence of asthma with sensiti zation to HDM and asymptomatic BHR as important risk factors for devel opment of asthma; the temporal relationship between sensitization to H DM and presence of airway abnormalities needs to be explored further.