title: Inverse association between farm animal contact and respiratory allergies in adulthood: protection, underreporting or selection?
abstract: BACKGROUND
  It has been argued that the inverse association between exposure to farm animals and nasal allergies observed in children and adults might be because of self-selection.
  
  
  OBJECTIVE
  We aimed to assess the health-based selection out of farming in adults.
  
  
  METHODS
  A cross-sectional study was carried out in a rural region. Overall, 4053 inhabitants (63%) aged 18-44 years responded to a questionnaire on respiratory diseases, life-time exposure to farming environments and potential confounders. For 2678 of these, specific immunoglobulin E to common allergens was available. The outcome was: (i) sensitization and symptoms of nasal allergies (symptomatic sensitization); (ii) sensitization without symptoms of nasal allergies (asymptomatic sensitization).
  
  
  RESULTS
  Farm animal contact in childhood was associated with a decreased risk of symptomatic and asymptomatic sensitization. Continued exposure to farm animals in adulthood further decreased the odds ratio of symptomatic (odds ratio 0.2; 95% confidence interval 0.1, 0.4) but not asymptomatic sensitization (0.7; 0.4, 1.1). Starting farm animal contact in adulthood even increased the odds ratio of asymptomatic sensitization (2.4; 1.1, 5.2).
  
  
  CONCLUSIONS
  The preventive effect of childhood contact to farm animals against sensitization continues into adulthood. However, in adulthood self-selection based on symptoms and underreporting of symptoms might also play a role.
authors.affiliation: Unit for Occupational and Environmental Epidemiology and Net Teaching, Institute for Occupational and Environmental Medicine, Ludwig-Maximilians-University, Munich, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Radon
authors.forename: A
authors.initials: A
authors.lastname: Schulze
authors.forename: D
authors.initials: D
authors.lastname: Nowak
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000485:Allergens / Q000276:immunology*; D000818:Animals; D000829:Animals, Domestic; D001249:Asthma / Q000517:prevention & control*; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged
chemical_list: D000485:Allergens