Dog exposure and subsequent asthma outcomes in children with asthma and allergy.

Background: While early-life dog exposure and its association with subsequent asthma is well studied, less is known about the impact of continuous or discontinued exposure on asthma outcomes in children with established asthma and allergy. Objectives: We sought to estimate the association between dog exposure and long-term asthma outcomes. Methods: A cohort study was conducted using Swedish national registers, following 99,389 children aged 3-16 years at asthma and allergy diagnosis until age 19, emigration, death, or year 2023. Dog exposure was categorized as "continuous" (parental dog ownership at diagnosis and throughout follow-up), "discontinued" (ownership ceased sometime after diagnosis), and "no exposure." Outcomes included moderate-to-severe asthma (defined by treatment steps) at 2-, 4-, and 6-year follow-up and asthma exacerbation (emergency visits and high short-acting β-2 agonist use) throughout follow-up. Results: In the cohort (median age 6.6 years; 41% female), 12.8% had continuous exposure and 1.2% had discontinued exposure. Compared to nonexposed, no association between continuous exposure and moderate-to-severe asthma was observed (adjusted odds ratio at 2-year follow-up: 1.00; 95% CI: 0.94-1.07); discontinued exposure showed similar result (adjusted odds ratio: 1.07; 95% CI: 0.93-1.23). However, both exposure groups had increased risk of exacerbations (continuous exposure: adjusted hazard ratio: 1.17; 95% CI: 1.06-1.29; and discontinued: hazard ratio: 1.52; 95% CI: 1.15-2.00), with no significant difference between the groups. Conclusion: In children with established asthma and allergy, continuous dog exposure does not seem to increase the risk of moderate-to-severe asthma, but it is associated with a modest increased risk of exacerbations. Discontinued exposure does not appear to improve asthma outcomes at the population level.