title: New-onset asthma and the effect of environment and occupation among farming and nonfarming rural subjects.
abstract: BACKGROUND
  Many factors, including environmental exposures, have been related to the increase in the prevalence of asthma, but only few have been tested for in longitudinal studies.
  
  
  OBJECTIVE
  We studied farming students to determine whether their environment during childhood and as adults was a factor determining subsequent onset of asthma.
  
  
  METHODS
  From 1994 to 1998, new cases of asthma were identified by means of an annual posted questionnaire followed by a telephone interview in a prospective cohort consisting of 1964 farming-school students and 407 nonfarming subjects aged 16 to 26 years. For each case, we selected a control subject from the cohort with no asthma in a case-based design, and all underwent an interview and a clinical examination.
  
  
  RESULTS
  We found 122 new cases of asthma. In a multiple regression model the odds ratio for new asthma was 3.3 (95% CI, 1.7-6.3) for smoking; 3.4 (95% CI, 1.6-7.0), 2.5 (95% CI, 1.1-5.3), and 7.0 (95% CI, 1.2-41.6) for exposure to swine, dairy production, and welding, respectively; and 11.7 (95% CI, 2.4-56.4) for bronchial hyperresponsiveness at baseline. Being born and raised on a farm significantly reduced the risk odds ratio (0.5 [95% CI, 0.3-0.98]), whereas atopy had no influence.
  
  
  CONCLUSIONS
  Exposure to swine and dairy confinements, welding, smoking, and bronchial hyperresponsiveness are risk factors for nonallergic asthma, and being born and raised on a farm reduces the subsequent risk. These findings support the theory that immune and inflammatory responses can be influenced by environmental exposure to early childhood, reducing the risk of asthma later in life.
authors.affiliation: Institute of Public Health, Department of Occupational and Environmental Medicine, University of Aarhus, Aarhus, Denmark. oo@rn.dk
authors.forename: Øyvind
authors.initials: Ø
authors.lastname: Omland
authors.forename: Charlotte
authors.initials: C
authors.lastname: Hjort
authors.forename: Ole Find
authors.initials: OF
authors.lastname: Pedersen
authors.forename: Martin R
authors.initials: MR
authors.lastname: Miller
authors.forename: Torben
authors.initials: T
authors.lastname: Sigsgaard
mesh_terms: D000293:Adolescent; D000328:Adult; D000383:Agriculture; D001249:Asthma / Q000453:epidemiology* / Q000209:etiology*; D004781:Environmental Exposure / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D016273:Occupational Exposure / Q000009:adverse effects*; D012307:Risk Factors; D012424:Rural Population; D011795:Surveys and Questionnaires; D006113:United Kingdom / Q000453:epidemiology