title: Effect of degree of urbanisation on age and sex-specific asthma prevalence in Swedish preschool children.
abstract: BACKGROUND
  There are few studies on age and sex-specific asthma prevalence in the age range 1-6 years. The purpose of this report was to estimate age and sex specific asthma prevalence in preschool children and to analyse the influence of possible demographic and geographic determinants.
  
  
  METHODS
  All 70 allergen avoidance day-care centres and 140 matched ordinary day-care centres across Sweden were sampled. The parents of all 8,757 children attending these day-care centres received the International Study of Asthma and Allergies in Childhood (ISAAC) written questionnaire, supplemented with questions on medical treatment, physician assessed asthma diagnosis, and other asthma related questions. The response rate was 68%.
  
  
  RESULTS
  The age specific asthma prevalence, adjusted for the underlying municipality population size, was among boys 9.7% at age 1, 11.1% at age 2, 11.4 at age 3, 10.5 at age 4, 8.7 at age 5, and 6.4 at age 6. The corresponding proportions among girls were 8.9%, 9.9%, 9.8%, 8.8%, 7.0%, and 5.0%, on average 9.6% for boys and 8.2% for girls, altogether 8.9%. In addition to age and sex the prevalence increased by municipality population density, a proxy for degree of urbanisation. Moreover, there was a remaining weak geographical gradient with increasing prevalence towards the north and the west.
  
  
  CONCLUSIONS
  The age-specific asthma prevalence was curvilinear with a peak around age 3 and somewhat higher for boys than for girls. The asthma prevalence increased in a slowly accelerating pace by municipality population density as a proxy for degree of urbanisation.
authors.affiliation: Department of Public Health and Caring Sciences, Family Medicine and Clinical Epidemiology, Uppsala University, Uppsala, Sweden. kristina.broms@pubcare.uu.se
authors.forename: Kristina
authors.initials: K
authors.lastname: Bröms
authors.forename: Dan
authors.initials: D
authors.lastname: Norbäck
authors.forename: Margaretha
authors.initials: M
authors.lastname: Eriksson
authors.forename: Claes
authors.initials: C
authors.lastname: Sundelin
authors.forename: Kurt
authors.initials: K
authors.lastname: Svärdsudd
mesh_terms: D000367:Age Factors; D001249:Asthma / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D015995:Prevalence; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology; D014507:Urbanization
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