title: Heredity, pet ownership, and confounding control in a population-based birth cohort.
abstract: BACKGROUND
  The association between pet ownership in childhood and subsequent allergic disease is controversial. Bias related to selection of pet exposure has been suggested as a reason for contradictory study results.
  
  
  OBJECTIVE
  The purpose of this investigation was to elucidate how pet exposure depends on family history of allergic disease, smoking, and socioeconomic factors in a prospective birth cohort.
  
  
  METHODS
  Parents of 4089 two-month-old children answered a questionnaire that included detailed questions about family history of asthma (maternal, paternal, and sibling), rhinoconjunctivitis, atopic eczema/dermatitis syndrome, pollen and pet allergy, smoking habits, parental occupation, and family pet ownership (cat and dog). Dust samples collected from the mothers' beds were analyzed for Fel d 1 and Can f 1 in a subgroup of the cohort.
  
  
  RESULTS
  Cats were less frequently kept in families with parental asthma, rhinoconjunctivitis, or pet or pollen allergy (3.5% to 5.8%) than in families without parental allergic disease (10.8% to 11.8%). Dogs were less common in families with (3.3%) than in families without (5.9%) parental atopic eczema/dermatitis syndrome. Families with smoking mothers and those with low socioeconomic index kept cats and dogs more frequently. Cat allergen levels were lower in homes with than in homes without maternal pet allergy, and this tended to hold true even for homes without a cat. Cat ownership decreased from birth to 2 years of age, especially in families with parental history of allergic diseases.
  
  
  CONCLUSIONS
  There seems to be a selection of pet exposure based on parental history of allergy, maternal smoking, and socioeconomic factors. This has to be taken into consideration in evaluations of risk associations between pet exposure and allergic disease in childhood.
authors.affiliation: Department of Occupational and Environmental Health, Karolinska Hospital, Stockholm, Sweden.
authors.forename: Catarina
authors.initials: C
authors.lastname: Almqvist
authors.forename: Ann-Charlotte
authors.initials: AC
authors.lastname: Egmar
authors.forename: Marianne
authors.initials: M
authors.lastname: van Hage-Hamsten
authors.forename: Niklas
authors.initials: N
authors.lastname: Berglind
authors.forename: Göran
authors.initials: G
authors.lastname: Pershagen
authors.forename: S Lennart
authors.initials: SL
authors.lastname: Nordvall
authors.forename: Magnus
authors.initials: M
authors.lastname: Svartengren
authors.forename: Gunilla
authors.initials: G
authors.lastname: Hedlin
authors.forename: Magnus
authors.initials: M
authors.lastname: Wickman
mesh_terms: D000818:Animals; D000829:Animals, Domestic / Q000276:immunology*; D015331:Cohort Studies; D006801:Humans; D006967:Hypersensitivity / Q000209:etiology* / Q000235:genetics; D007223:Infant; D015999:Multivariate Analysis; D011446:Prospective Studies; D012907:Smoking / Q000009:adverse effects; D012959:Socioeconomic Factors