The role of climate on the geographic variability of asthma, allergic rhinitis and respiratory symptoms: results from the Italian study of asthma in young adults

Background: Variations in the prevalence of respiratory symptoms according to geo-climatic factors could provide important clues to the knowledge of the aetiology of asthma. Methods: Geo-climatic variations in the prevalence of current asthma, allergic rhinitis and chronic cough, and phlegm were assessed on a random sample of 18 873 subjects (response rate = 72.7%) from different climatic regions of Italy. An ecological analysis, supported by robust statistical methods, was employed to investigate potential trends. Results: The prevalence of all symptoms was significantly heterogeneous throughout the peninsula. Only asthma-like symptoms showed a north–south trend: the prevalence increased at a decreasing latitude [odds ratio (OR) varies from 0.92 to 0.96, P