title: Childhood asthma in four regions in Scandinavia: risk factors and avoidance effects.
abstract: BACKGROUND
  The high and increasing prevalence of childhood asthma is a major public health issue. Various risk factors have been proposed in local studies with different designs.
  
  
  METHODS
  We have made a questionnaire study of the prevalence of childhood asthma, potential risk factors and their relations in four regions in Scandinavia (Umeå and Malmö in Sweden, Kuopio in eastern Finland and Oslo, Norway). One urban and one less urbanized area were selected in each region, and a study group of 15962 children aged 6-12 years was recruited.
  
  
  RESULTS
  The prevalence of symptoms suggestive of asthma varied considerably between different areas (dry cough 8-19%, asthma attacks 4-8%, physician-diagnosed asthma 4-9%), as did the potential risk factors. Urban residency was generally not a risk factor. However, dry cough was common in the most traffic polluted area. Exposure to some of the risk factors. such as smoking indoors and moisture stains or moulds at home during the first 2 years of life, resulted in an increased risk. However, current exposure was associated with odds ratios less than one.
  
  
  CONCLUSIONS
  Our findings were probably due to a combination of early impact and later avoidance of these risk factors. The effects of some risk factors were found to differ significantly between regions. No overall pattern between air pollution and asthma was seen, but air pollution differed less than expected between the areas.
authors.affiliation: Department of Environmental Health, Umeå University, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Forsberg
authors.forename: J
authors.initials: J
authors.lastname: Pekkanen
authors.forename: J
authors.initials: J
authors.lastname: Clench-Aas
authors.forename: M B
authors.initials: MB
authors.lastname: Mårtensson
authors.forename: N
authors.initials: N
authors.lastname: Stjernberg
authors.forename: A
authors.initials: A
authors.lastname: Bartonova
authors.forename: K L
authors.initials: KL
authors.lastname: Timonen
authors.forename: S
authors.initials: S
authors.lastname: Skerfving
mesh_terms: D000397:Air Pollution / Q000706:statistics & numerical data*; D016902:Air Pollution, Indoor / Q000706:statistics & numerical data; D001249:Asthma / Q000453:epidemiology*; D002648:Child; D016001:Confidence Intervals; D003371:Cough / Q000453:epidemiology; D003430:Cross-Sectional Studies; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D005192:Family Health; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D015995:Prevalence; D012111:Residence Characteristics / Q000706:statistics & numerical data; D012189:Retrospective Studies; D012307:Risk Factors; D012537:Scandinavian and Nordic Countries / Q000453:epidemiology; D012737:Sex Factors; D011795:Surveys and Questionnaires; D014504:Urban Health / Q000706:statistics & numerical data