title: Change in prevalence of asthma in Danish children and adolescents.
abstract: BACKGROUND
  There is evidence suggesting that the prevalence of asthma has increased, especially in industrialized countries.
  
  
  OBJECTIVE
  To investigate whether the prevalence of asthma in Danish children and adolescents has changed during the past 15 years.
  
  
  METHODS
  Serial cross-sectional studies of 2 different random population samples of children aged 7 to 17 years, living in urban Copenhagen, Denmark, were performed 15 years apart. The first cohort was investigated in 1986 (n = 527) and the second in 2001 (n = 480). The same methods were applied at both occasions. Skin test reactivity was measured using standard techniques. Asthma was defined on the basis of questionnaire responses and was regarded as nonatopic (intrinsic) if no positive reactions were observed on the skin test and as atopic (extrinsic) if at least 1 positive reaction was noted. Current asthma was defined as symptoms within the preceding 12 months.
  
  
  RESULTS
  The prevalence of current asthma increased from 5.3% in 1986 to 11.7% in 2001. This was primarily due to an increase in intrinsic asthma, which was 4.2-fold (1.5% to 6.4%), compared with extrinsic asthma, which increased only 1.4-fold (3.8% to 5.5%). The changes were more pronounced in girls.
  
  
  CONCLUSIONS
  The prevalence of asthma has increased substantially during the past 15 years. The observed striking increase in intrinsic asthma suggests the possibility of a more heterogeneous disorder, involving more important factors than atopy. Furthermore, our findings suggest that asthma might be shifting toward female predominance in childhood.
authors.affiliation: Department of Internal Medicine, Bispebjerg Hospital, Copenhagen, Denmark. sft@city.dk
authors.forename: Simon F
authors.initials: SF
authors.lastname: Thomsen
authors.forename: Charlotte S
authors.initials: CS
authors.lastname: Ulrik
authors.forename: Klaus
authors.initials: K
authors.lastname: Larsen
authors.forename: Vibeke
authors.initials: V
authors.lastname: Backer
mesh_terms: D000293:Adolescent; D000367:Age Factors; D001249:Asthma / Q000453:epidemiology*; D002648:Child; D003430:Cross-Sectional Studies; D003718:Denmark; D005260:Female; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000453:epidemiology; D008137:Longitudinal Studies; D008297:Male; D015995:Prevalence; D012737:Sex Factors; D012882:Skin Tests; D011795:Surveys and Questionnaires