Asthma in every fifth child in Oslo, Norway: a 10‐year follow up of a birth cohort study*

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Abstract
Background:  The western world's increase in childhood asthma is suggested to level off. We aimed to investigate asthma prevalence in 10‐year‐old children within the prospective birth cohort Environment and Childhood Asthma (ECA) Study in Oslo established in 1992/1993.Subjects and methods:  Six hundred and sixteen (77%) of 803 children (mean age 10.9 ± 0.9 (SD) years) with lung function measurements at birth were reinvestigated at age 10 years. At birth they corresponded to the entire birth cohort (n = 3754) regarding gender, socio‐demographic factors, parental allergic diseases, pet keeping and maternal smoking. Results from structured parental interview, spirometry, and skin prick test for inhalant and food allergens are presented. Asthma definition required minimum two positive criteria, (i) doctor's diagnosis of asthma, (ii) wheeze and/or chest tightness, (iii) use of anti‐asthmatic treatment. Current asthma required asthma definition plus either (ii) and/or (iii) in the last 12 months, and/or ≥10% fall in forced expired volume in 1 s after treadmill running.Results:  Lifetime prevalence of asthma was 20.2%; current asthma 11.1%, doctor diagnosis of asthma 16.1% and wheezes ever 30.3%. Allergic sensitization (29.3% overall) was more common among children with current (56.3%) compared to asymptomatic (last 12 months) (26.0%) or no asthma (27.6%) (P < 0.001). Boys more often than girls had current asthma (14.4 vs 7.1%, P = 0.004), wheeze ever (36.9 vs 22.5%, P = 0.002) and allergic sensitization (36.2 vs 22.1%, respectively, P < 0.001).Conclusion:  Childhood asthma apparently continues to increase in Oslo, having affected every fifth 10‐year‐old child.