Latitude variation in the prevalence of asthma and allergic rhinitis in Italy: Results from the GEIRD study

BACKGROUND: Earlier studies have pointed out a great variability in the prevalence of asthma and asthma-like symptoms in different geo-climatic areas. AIM: To test the association between latitude and prevalence of asthma and allergic rhinitis in Italian young adults. METHODS: In the frame of Gene-Environment Interaction in Respiratory Diseases study, a postal screening questionnaire on respiratory health and exposure to environmental factors was administered to 18,357 randomly selected subjects aged 20-44 years in 7 centres: 3 in Northern (Torino, Pavia, Verona), 2 in Central (Ancona, Perugia) and 2 in Southern Italy (Salerno, Sassari). RESULTS: 10,494 (57.2%) subjects responded to the questionnaire. The prevalence of self-reported doctor-diagnosed asthma and allergic rhinitis in the lifespan was 10.2% and 26.9%, respectively, and was significantly different across the centres (p<0.05). After adjusting for sex, age, potential risk factors for respiratory diseases and design confounders, the prevalence of asthma (OR: 1.07 per 1°latitude decrease, p<0.001), asthma-like symptoms (wheezing, chest tightness, asthma attacks: OR ranging from 1.04 to 1.06, p<0.05) and allergic rhinitis (OR: 1.03, p=0.04) showed a significant north-to-south trend. Similarly, a 1°C increment in temperature was significantly associated with asthma (OR: 1.10, p<0.001) and asthma-like symptoms (OR from 1.07 to 1.10, p<0.05), but not with allergic rhinitis (OR=1.02, p=0.190). CONCLUSION: The prevalence of asthma and allergic rhinitis increased moving southwards in Italy, suggesting that prolonged exposure to different geo-climatic conditions may affect the onset of asthma and allergic respiratory diseases.