Combined exposure to dog and indoor pollution: incident asthma in a high-risk birth cohort

The impact of single exposures on asthma development is better understood than the effect of multiple exposures. The objective of the present study was to evaluate the effect of combined early exposure to dog allergen (Can-f1) plus indoor nitrogen dioxide (NO₂) or environmental tobacco smoke (ETS) on asthma and bronchial hyperreactivity (BHR) in a high-risk birth cohort. We also aimed to assess atopy's impact on the effects of these exposures. Peri-birth ETS exposure was measured using cord blood cotinine (CCot). During year 1, atopy, NO₂, Can-f1, and urinary cotinine (UCot) were measured. At 7 yrs of age, 380 children were assessed for asthma and BHR. Exposure effects were determined using stepwise multiple linear regression. Co-exposure to elevated Can-f1 and NO₂, or Can-f1 and ETS (CCot), increased risk for asthma, relative to having neither such exposure (OR 4.8 (95% CI 1.1-21.5) and 2.7 (1.1-7.1), respectively); similar risks resulted when substituting dog ownership for allergen. Atopy increased asthma and BHR risk associated with several exposures; notably, atopy with elevated UCot, relative to atopy without such exposure, increased risk of BHR (OR 3.1 (95% CI 1.1-8.6)). In a high-risk birth cohort, early co-exposure to Can-f1 and NO₂ or ETS increased the risk of incident asthma. Atopy increased the risk of asthma and BHR associated with ETS.