Severe asthma in childhood: assessed in 10 year olds in a birth cohort study.

BACKGROUND: Limited information is available regarding the prevalence of severe asthma in children. The present study aimed at investigating the prevalence of severe asthma in an urban child population; secondarily evaluating the applicability of the chosen definition by clinical characteristics.
METHODS: Children enrolled in the prospective birth cohort; the Environment and Childhood Asthma Study in Oslo; were reinvestigated at the age of 10 years (n = 1019). A representative population based cohort of 616 children [mean age 10.9 (SD 0.9) years] with lung function measurements at birth was used for prevalence estimates, whereas all 1019 children (154 with current asthma) attending the 10-year follow-up were included for verification of the definition of severe asthma. Clinical investigations included spirometry, tests of bronchial hyperresponsiveness, skin prick tests and exhaled nitric oxide. Severe asthma was defined as poorly controlled asthma despite treatment with > or = 800 microg budesonide or equivalent; assessed by a detailed structured interview.
RESULTS: The population point prevalence at age 10 years of current severe asthma was 0.5% (three of 616) and among children with current asthma 4.5% (three of 67). The 10/154 children identified as suffering from severe asthma more often had severe bronchial hyperresponsiveness (PD(20) methacholine <1 micromol) (60%vs 22%, P = 0.015), lower median forced expiratory volume in 1 s/forced vital capacity ratio (93%vs 99%, P = 0.04) and higher body mass index (mean BMI 22.3 vs 18.3, P < 0.001) than nonsevere current asthmatics.
CONCLUSIONS: The prevalence of severe asthma was 0.5% in all 10-year olds, and 4.5% among current asthmatics. The severe asthma definition applied in this study is supported by results of clinical investigations.