Exposure to secondhand tobacco smoke enhances respiratory symptoms and responses to animals in 8,819 children in kindergarten: results from 25 districts in northeast China.

BACKGROUND Experimental data suggest that asthma exacerbation by allergens is enhanced by exposure to environmental tobacco smoke (ETS); however, there is little supporting epidemiologic evidence. To our knowledge, few studies have assessed respiratory symptoms and allergies in this context. OBJECTIVES To evaluate whether the association of exposure to animals (indicators of allergen and endotoxin exposure) with asthma-related symptoms is modified by ETS exposure in Chinese children. METHODS A cross-sectional study of 8,819 children in kindergarten was conducted in 25 districts in northern China. Information on respiratory health and exposure to indoor allergens was obtained using a standard questionnaire from the American Thoracic Society. RESULTS Among the children with ETS exposure in utero, the effects of exposure to animals were significant with respect to persistent cough [adjusted odds ratio (OR) 1.83; 95% confidence interval (CI) 1.12-2.99] and persistent phlegm (adjusted OR 2.40; 95% CI 1.28-4.54). The combined effect of in utero ETS exposure and animal exposure on doctor-diagnosed asthma was approximately as expected on the basis of their independent effects on an additive scale. There was no interaction between animal exposure and ETS exposure in the first 2 years of life or current ETS exposure. CONCLUSIONS This study provides evidence that animal and ETS exposure increases the risk of asthma-related symptoms in children in kindergarten. ETS exposure in utero did modify the effect of animal exposure on persistent phlegm and persistent cough but not on doctor-diagnosed asthma among children.