title: Prevalence of severe childhood asthma according to the WHO.
abstract: BACKGROUND
  The World Health Organization (WHO) recently proposed a new definition of severe asthma to facilitate standardized characterization of patients, and enable more accurate estimations of the prevalence of severe asthma. The aim of this study was to estimate the prevalence of severe asthma according to the WHO definition in children aged 12 years, in Stockholm, Sweden.
  
  
  METHODS
  The birth cohort BAMSE enrolled 4089 children during 1994-96. Parental questionnaires provided information on asthma-related symptoms, diagnosis and medication from 3015 enrolled children at the age of 12 years. Severe asthma was defined as the presence of asthma, as well as continuous treatment with inhaled corticosteroids and long-acting beta-2 agonists, based on information from the Swedish prescribed drug register demonstrating prescriptions of at least 800 μg budesonide daily (or equivalent).
  
  
  RESULTS
  The prevalence of asthma was 11% among 12-year-olds (n = 329). Based on information from the Swedish prescribed drug register, seven children with asthma fulfilled the definition of severe asthma. The estimated prevalence corresponds to 0.23% (95% CI, 0.06-0.4) of the population, or 2.1% (95% CI, 0.5-3.7) of children with asthma. Based on assessed markers of asthma control, 3/7 with severe asthma were considered to have controlled asthma and 4/7 had partly or uncontrolled asthma.
  
  
  CONCLUSIONS
  Severe asthma appears rare both among 12-year-old schoolchildren with asthma and in the general population. Combining self-reported information from a population-based birth cohort with data from a drug register seems trustworthy in estimating severe asthma as defined by the WHO.
authors.affiliation: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden; Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden. Electronic address: bjorn.nordlund@ki.se.
authors.forename: Björn
authors.initials: B
authors.lastname: Nordlund
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; Centre for Allergy Research, Karolinska Institutet, Stockholm, Sweden; Sachs' Children's Hospital, Södersjukhuset, Stockholm, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Melén
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Erica S
authors.initials: ES
authors.lastname: Schultz
authors.affiliation: Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Grönlund
authors.affiliation: Astrid Lindgren Children's Hospital, Karolinska University Hospital, Stockholm, Sweden; Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden; Centre for Allergy Research, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Gunilla
authors.initials: G
authors.lastname: Hedlin
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden; Sachs' Children's Hospital, Södersjukhuset, Stockholm, Sweden; Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Inger
authors.initials: I
authors.lastname: Kull
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000453:epidemiology*; D002648:Child; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D015995:Prevalence; D013548:Sweden / Q000453:epidemiology
keywords: Asthma; Population-based study; Prevalence; Severe asthma; WHO