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.

Abstract

Variations in the prevalence of respiratory symptoms according to geo-climatic factors could provide important clues to the knowledge of the aetiology of asthma. 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. 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 < 0.05], at a decreasing distance from the sea (OR: 0.90-0.93 for 30 km distance, P < 0.05), at higher annual mean temperatures (OR: 1.11-1.14, P < 0.05) and at smaller annual temperature ranges (OR: 0.94-0.95, P < 0.05). Of the geo-climatic variables considered, temperature range had the greatest influence on most asthma-like symptoms. No association was found between geo-climatic variables and allergic rhinitis or chronic cough and phlegm. Asthma prevalence seems to be significantly affected by climate as asthma-like symptoms were more common in central-southern Italy, with a Mediterranean climate, than in areas with a continental climate (northern Italy).