Longitudinal changes in atopy during a 4-year period: relation to bronchial hyperresponsiveness and respiratory symptoms in a population sample of Australian schoolchildren.

A total of 380 schoolchildren living in Belmont, New South Wales, a coastal town where the predominant aeroallergens are house dust mites, were studied on three occasions at 2-year intervals. At each study, atopy was measured by skin prick tests to 13 allergens, bronchial responsiveness was measured by histamine inhalation test, and respiratory illness history was assessed by a self-administered questionnaire to parents. The age of the group was 8 to 10 years at enrollment. We found that skin wheals less than 4 mm were not associated with respiratory or allergic illness, and therefore, we defined atopy as the presence of a skin wheal of greater than or equal to 4 mm. In the sample, 24% of the children were atopic at 8 to 10 years (early-onset atopy), and an additional 15% became atopic during the study (late-onset atopy). Both early- and late-onset atopy had a close association with hay fever. Late-onset atopy was strongly associated with inconsistent reporting of symptoms. Early-onset atopy was an important risk factor for bronchial hyperresponsiveness (BHR), diagnosed asthma, and continuing symptoms of wheeze, and was a particularly important risk factor for BHR with current wheeze in late childhood years. We conclude that atopy acquired at an early age is an important predictive factor for respiratory symptoms occurring with BHR and continuing into late childhood.