Does Early Exposure to Animals Alter Risk of Childhood Asthma?

In this cohort study, the association between early exposure to dogs and farm animals and the risk of asthma was evaluated and included all children born in Sweden. The association was assessed as the odds ratio (OR) for a current diagnosis of asthma at age 6 years for schoolaged children and as the hazard ratio (HR) for incident asthma at ages 1 to 5 years for preschool-aged children. The primary outcome was childhood asthma diagnosis and medication used. Of the 1 011 051 children born during the study period, 376 638 preschool-aged (53 460 [14.2%] exposed to dogs and 1729 [0.5%] exposed to farm animals) and 276 298 school-aged children (22 629 [8.2%] exposed to dogs and 958 [0.3%] exposed to farm animals) were included in the analyses. Of these, 18 799 children (5.0%) in the preschool-aged children’s cohort experienced an asthmatic event before baseline, and 28 511 cases of asthma and 906 071 years at risk were recorded during follow-up (incidence rate, 3.1 cases per 1000 years at risk). In the school-aged children’s cohort, 11 585 children (4.2%) experienced an asthmatic event during the seventh year of life. Dog exposure during the first year of life was associated with a decreased risk of asthma in school-aged children (OR, 0.87; 95% CI, 0.810.93) and in preschool-aged children 3 years or older (HR, 0.90; 95%CI, 0.83-0.99) but not in children younger than 3 years (HR, 1.03; 95% CI, 1.00-1.07). Farm animal exposure was associated with a reduced risk of asthma in both school-aged children and preschool-aged children (OR, 0.48; 95%CI, 0.31-0.76, and HR, 0.69; 95%CI, 0.56-0.84), respectively. The authors conclude that exposure to dogs and farm animals during the first year of life reduce the risk of asthma in children at age 6 years.