Associations of Early Life Exposures and Environmental Factors With Asthma Among Children in Rural and Urban Areas of Guangdong, China

Background Environmental factors may play important roles in asthma, but findings have been inconsistent. Objective The goal of this study was to determine the associations between early life exposures, environmental factors, and asthma in urban and rural children in southeast China. Methods A screening questionnaire survey was conducted in 7,164 children from urban Guangzhou and 6,087 from rural Conghua. In the second stage, subsamples of 854 children (419 from Guangzhou, 435 from Conghua) were recruited for a case-control study that included a detailed questionnaire enquiring on family history, early life environmental exposures, dietary habits, and laboratory tests (including histamine airway provocation testing, skin prick tests, and serum antibody analyses). House dust samples from 76 Guangzhou families and 80 Conghua families were obtained to analyze levels of endotoxins, house dust mites, and cockroach allergens. Results According to the screening survey, the prevalence of physician-diagnosed asthma was lower in children from Conghua (3.4%) than in those from Guangzhou (6.9%) ( P P Dermatophagoides farinae group 1 allergen (OR, 1.71 [95% CI, 1.34-2.19]) were positively associated with asthma. Living in a crop-farming family at  Conclusions Rural children from an agricultural background exhibited a reduced risk of asthma. Early life exposure to crop farming and high environmental endotoxin levels might protect the children from asthma in southern China.