title: Does pet ownership in infancy lead to asthma or allergy at school age? Pooled analysis of individual participant data from 11 European birth cohorts.
abstract: OBJECTIVE
  To examine the associations between pet keeping in early childhood and asthma and allergies in children aged 6-10 years.
  
  
  METHODS
  Pooled analysis of individual participant data of 11 prospective European birth cohorts that recruited a total of over 22,000 children in the 1990s.  EXPOSURE DEFINITION: Ownership of only cats, dogs, birds, rodents, or cats/dogs combined during the first 2 years of life.  OUTCOME DEFINITION: Current asthma (primary outcome), allergic asthma, allergic rhinitis and allergic sensitization during 6-10 years of age.
  
  
  RESULTS
  Three-step approach: (i) Common definition of outcome and exposure variables across cohorts; (ii) calculation of adjusted effect estimates for each cohort; (iii) pooling of effect estimates by using random effects meta-analysis models.
  
  
  RESULTS
  We found no association between furry and feathered pet keeping early in life and asthma in school age. For example, the odds ratio for asthma comparing cat ownership with "no pets" (10 studies, 11489 participants) was 1.00 (95% confidence interval 0.78 to 1.28) (I(2) = 9%; p = 0.36). The odds ratio for asthma comparing dog ownership with "no pets" (9 studies, 11433 participants) was 0.77 (0.58 to 1.03) (I(2) = 0%, p = 0.89). Owning both cat(s) and dog(s) compared to "no pets" resulted in an odds ratio of 1.04 (0.59 to 1.84) (I(2) = 33%, p = 0.18). Similarly, for allergic asthma and for allergic rhinitis we did not find associations regarding any type of pet ownership early in life. However, we found some evidence for an association between ownership of furry pets during the first 2 years of life and reduced likelihood of becoming sensitized to aero-allergens.
  
  
  CONCLUSIONS
  Pet ownership in early life did not appear to either increase or reduce the risk of asthma or allergic rhinitis symptoms in children aged 6-10. Advice from health care practitioners to avoid or to specifically acquire pets for primary prevention of asthma or allergic rhinitis in children should not be given.
authors.affiliation: Department of Paediatrics, Oslo University Hospital, Ullevål, Norway.
authors.forename: Karin C
authors.initials: KC
authors.lastname: Lødrup Carlsen
authors.forename: Stephanie
authors.initials: S
authors.lastname: Roll
authors.forename: Kai-Håkon
authors.initials: KH
authors.lastname: Carlsen
authors.forename: Petter
authors.initials: P
authors.lastname: Mowinckel
authors.forename: Alet H
authors.initials: AH
authors.lastname: Wijga
authors.forename: Bert
authors.initials: B
authors.lastname: Brunekreef
authors.forename: Maties
authors.initials: M
authors.lastname: Torrent
authors.forename: Graham
authors.initials: G
authors.lastname: Roberts
authors.forename: S Hasan
authors.initials: SH
authors.lastname: Arshad
authors.forename: Inger
authors.initials: I
authors.lastname: Kull
authors.forename: Ursula
authors.initials: U
authors.lastname: Krämer
authors.forename: Andrea
authors.initials: A
authors.lastname: von Berg
authors.forename: Esben
authors.initials: E
authors.lastname: Eller
authors.forename: Arne
authors.initials: A
authors.lastname: Høst
authors.forename: Claudia
authors.initials: C
authors.lastname: Kuehni
authors.forename: Ben
authors.initials: B
authors.lastname: Spycher
authors.forename: Jordi
authors.initials: J
authors.lastname: Sunyer
authors.forename: Chih-Mei
authors.initials: CM
authors.lastname: Chen
authors.forename: Andreas
authors.initials: A
authors.lastname: Reich
authors.forename: Anna
authors.initials: A
authors.lastname: Asarnoj
authors.forename: Carmen
authors.initials: C
authors.lastname: Puig
authors.forename: Olf
authors.initials: O
authors.lastname: Herbarth
authors.forename: Jestinah M
authors.initials: JM
authors.lastname: Mahachie John
authors.forename: Kristel
authors.initials: K
authors.lastname: Van Steen
authors.forename: Stefan N
authors.initials: SN
authors.lastname: Willich
authors.forename: Ulrich
authors.initials: U
authors.lastname: Wahn
authors.forename: Susanne
authors.initials: S
authors.lastname: Lau
authors.forename: Thomas
authors.initials: T
authors.lastname: Keil
mesh_terms: D000485:Allergens / Q000276:immunology; D000818:Animals; D001249:Asthma / Q000209:etiology*; D001717:Birds; D002415:Cats; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004285:Dogs; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000209:etiology*; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D016017:Odds Ratio; D057805:Pets; D012306:Risk; D012377:Rodentia
chemical_list: D000485:Allergens