Protective factors against childhood asthma in rural China

The prevalence of childhood asthma has increased significantly over the past few decades. One consistent finding of many epidemiological studies was the dramatic protection against the development of asthma in rural or farming environment. Livestock exposure and consumption of farm milk were the major factors explaining the protection in central Europe. Previous study in China revealed that the predominately agricultural environment also conferred such protection. This study aims to identify the possible factors accounting for the rural protection in China. Random samples of school children aged 5 to 7 were recruited from Hong Kong and rural China (Conghua). Conghua is a rural area in Southern China 200 kilometers north of Hong Kong. The parents completed a detailed questionnaire including the validated ISAAC core questionnaires and an environmental questionnaire to ascertain the possible environmental risk factors in rural Conghua. A total of 17,587 children (14,152 from Conghua and 3,435 from Hong Kong) were successfully recruited. In Conghua, the reported prevalence of current wheeze, current rhinoconjuntivitis, and current eczema were 1.7%, 2.7%, and 4.4% respectively. These rates were significantly (P