• Mulin Feng, Zhaowei Yang, Liying Pan, Xuxin Lai, Mo Xian, Xiafei Huang, Yan Chen, Paul C Schröder, Marjut Roponen, Bianca Schaub, Gary W K Wong, and Jing Li.
• Department of Allergy and Clinical Immunology, State Key Laboratory of Respiratory Disease, The First Affiliated Hospital, Guangzhou Medical University, Guangzhou, China.
• Chest. 2016 Apr 1; 149 (4): 1030-41.

BackgroundEnvironmental factors may play important roles in asthma, but findings have been inconsistent.ObjectiveThe 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.MethodsA 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.ResultsAccording 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 < .001). A lower percentage of asthma was reported in rural subjects compared with urban subjects (2.8% vs. 29.4%; P < .001) in the case-control study. Atopy (OR, 1.91 [95% CI, 1.58-2.29]), parental atopy (OR, 2.49 [95% CI, 1.55-4.01]), hospitalization before 3 years of age (OR, 2.54 [95% CI, 1.37-4.70]), high consumption of milk products (OR, 1.68 [95% CI, 1.03-2.73]), and dust 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 < 1 year of age (OR, 0.15 [95% CI, 0.08-0.32]) and dust endotoxin levels (OR, 0.69 [95% CI, 0.50-0.95]) were negatively associated with asthma.ConclusionsRural 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.Copyright © 2016 American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.

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