The prevalence of asthma has been documented to be increasing over the past few decades. Within the Chinese population, the prevalence of childhood asthma has been found to be the highest in Hong Kong compared with Beijing and Guangzhou.

To investigate the environmental lifestyle risk factors which may explain the disparity of asthma prevalence in the Chinese population.

In a cross-sectional study, 10 902 schoolchildren were recruited from Hong Kong (n=3110), Beijing (n=4277), and Guangzhou (n=3565) using the ISAAC PhaseⅡprotocol. The average age of the children among three cities was 10.1-10.4 years and 50%-53% were male. Each subject was given an ISAAC Phase Ⅱ questionnaire to be completed by the parents or guardians. Random subgroups of at least 1000 children from each city, added up to 3479 children underwent skin-prick testing. The sensitivity to eight common aeroallergens was assessed. Logistic regression analysis was used to determine the environmental and lifestyle risk factors for asthma and atopy.

The prevalence of wheezing in the past 12 months (Hong Kong, 5.8%; Beijing, 3.8%; Guangzhou, 3.4%) was significantly higher in schoolchildren from Hong Kong than that from the Mainland of China (OR 1.64, 95%CI 1.35-1.99). Multivariate logistic regression analyses revealed that the use of gas cooking (OR 2.08, 95%CI 1.32-3.26), foam pillow (OR 1.94, 95%CI 1.19-3.16), and house dampness (OR 1.84, 95%CI 1.25-2.71) were significant risk factors for "current wheezing" . The use of cotton quilt (OR 0.70, 95%CI 0.56-0.87), breast-feeding (OR 0.79, 95%CI 0.66-0.96), and attendance of daycare (OR 0.73, 95%CI 0.59-0.88) were protective factors against "current wheezing" . When a summary measure of these variables was introduced into a regression model, the Mainland residency was no longer associated with "current asthma" or "current wheezing" suggesting that either these factors or other unmeasured factors associated with above factors are responsible for the lower prevalence of asthma in the Mainland of China.

Several environmental and lifestyle factors represented characteristic of life in Mainland of China, including breast feeding, attendance of daycare, use of cotton quilt, use of pillow other than foam pillow, use of cooking fuel other than gas, and the absence of damp spots on the walls or ceiling, were the significant risk factors contributed to the disparity of asthma prevalence in children from Hong Kong and the Mainland of China.

Asthma; Child; Prevalence; Life style; Risk factor