Factors associated with difference in prevalence of asthma in children from three cities in China: multicentre epidemiological survey.

OBJECTIVE To determine the factors associated with difference in prevalence of asthma in children in different regions of China. DESIGN Multicentre epidemiological survey. SETTING Three cities in China. PARTICIPANTS 10,902 schoolchildren aged 10 years. MAIN OUTCOME MEASURES Asthma and atopic symptoms, atopic sensitisation, and early and current exposure to environmental factors. RESULTS Children from Hong Kong had a significantly higher prevalence of wheeze in the past year than those from Guangzhou and Beijing (odds ratio 1.64, 95% confidence interval 1.35 to 1.99). Factors during the first year of life and currently that were significantly associated with wheeze were cooking with gas (odds ratio 2.04, 1.34 to 3.13), foam pillows (2.58, 1.66 to 3.99), and damp housing (1.89, 1.26 to 2.83). Factors protecting against wheeze were cotton quilts and the consumption of fruit and raw vegetables. CONCLUSION Environmental factors and diet may explain the differences in prevalence of asthma between children living in different regions of China.