Objective: We aimed to explore associations between natural history and environmental factors and asthma in urban and rural children in China.
Methods: A questionnaire survey was performed in 7164 children from urban Guangzhou and 6087 from rural Conghua. Subsamples of 854 children (419 from Guangzhou, 435 from Conghua) were recruited for case-control study including detail questionnaire for natural and family history, environmental exposure and eating behaviors, histamine airway provocation, allergen skin prick test, and serum antibody analysis. House dust samples from 76 Guangzhou and 80 Conghua families were obtained to analyze levels of endotoxin, house dust mite and cockroach allergens.
Results: The prevalence of doctor-diagnosed-asthma was lower in children from Conghua (3.4%) than Guangzhou (6.9%, p<0.001) in the screening survey. A lower percentage for confirmed asthma (3.0% vs 28.9%) and sensitization (13.3% vs 50.6%) was found in rural than urban subjects (p<0.001) in the nested case-control study. Parental allergy (3.30 [2.08-5.24]), antibiotic usage (3.29 [1.93-5.60]), high frequency of milk consumption (2.31 [1.45-3.68]) and increased level of house dust Der f 1 (1.71 [1.34-2.19]) were positively associated with confirmed asthma (p<0.001). Breastfeeding (0.62 [0.39-0.97]), raising dogs (0.50 [0.26-0.94]) and level of house dust endotoxin (0.69 [0.50-0.95]) were negatively associated with confirmed asthma (p<0.05).
Conclusions: Parental allergy, early antibiotic administration, high frequency of milk intake and level of Der f 1 exposure might be risk factors for asthma, while breastfeeding, dog ownership and endotoxin exposure were protective.