Cold air challenge at age 6 and subsequent incidence of asthma. A longitudinal study

The aim of this study was to assess the relation between bronchial hyperresponsiveness to dry, cold air at age 6 and the subsequent incidence of asthma. The cumulative incidence of newly diagnosed asthma between ages 6 and 11 among 360 children included in this study was 12.0%. Survival analysis showed that hyperresponsiveness to cold air at age 6 was associated with an increased risk of developing subsequent asthma (hazard ratio = 2.6, 95% Cl = 1.2-5.4; p = 0.01). However, after adjusting for potential confounders, only mild wheezing at age 6 (adjusted hazard ratio = 7.5, 95% Cl = 3.6-15.9; p < 0.001) and skin test reactivity to allergens at age 6 (adjusted hazard ratio = 3.6, 95% Cl = 1.5-8.5; p < 0.01), but not hyperresponsiveness to cold air (adjusted hazard ratio = 0.9, 95% Cl = 0.4-2.2; p = 0.8), remained significant predictors of subsequent development of asthma. These findings were substantially confirmed after stratifying for wheezing illnesses before age 3. We conclude that hyperresponsiveness to cold air at age 6 was associated with subsequent development of a diagnosis of asthma but this effect was not independent of atopy and mild wheezing at age 6.