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.

Design: 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.

Data synthesis: 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.

Figure 1. Current asthma.

Meta-analyses of the adjusted odds ratios of asthma at 6–10 years of age and pet ownership in the first 2 years of life for: A), cat only vs. no pets; B), dog only vs. no pets; C) cat and dog only vs. no pets; D) bird only vs. no pets; E) rodents only vs. no pets.

Figure 2. Allergic asthma.

Meta-analyses of the adjusted odds of allergic asthma (sensitized to at least 1 aero-allergen; secondary endpoint) in early school age and ownership of pets in the first 2 years of life for: A), cat only vs. no pets; B), dog only vs. no pets; C) cat and dog only vs. no pets; D) bird only vs. no pets; E) rodents only vs. no pets.

Figure 3. Allergic sensitization.

Meta-analyses of the adjusted odds of allergic sensitization (sensitized to at least 1 aero-allergen) in early school age and pet ownership in the first 2 years of life for: A), cat only vs. no pets; B), dog only vs. no pets; C) cat and dog only vs. no pets; D) bird only vs. no pets; E) rodents only vs. no pets. (There were no IgE data available for Leicester 1998 cohort.)

Figure 4. Allergic rhinitis.

Meta-analyses of the adjusted odds of allergic rhinitis (sensitized to at least 1 aero-allergen; secondary endpoint) in early school age and pet ownership in the first 2 years of life for: A), cat only vs. no pets; B), dog only vs. no pets; C) cat and dog only vs. no pets; D) bird only vs. no pets; E) rodents only vs. no pets.