1. Unit of Epidemiology and Medical Statistics; Department of Public Health and Community Medicine; University of Verona; Verona Italy
2. Unit of Respiratory Medicine and Allergology; CPA-ASL TO-2; Turin Italy
3. Department of Internal Medicine; Immuno-Allergic and Respiratory Diseases; Ospedali Riuniti di Ancona; Ancona Italy
4. Section of Internal Medicine; University of Verona; Verona Italy
5. Institute of Respiratory Diseases; University of Sassari; Sassari Italy
6. Unit of Occupational Medicine; AO Istituti Ospedalieri di Verona; Verona Italy
7. Department of Experimental Medicine; University of Perugia; Perugia Italy
8. Department of Public Health and Pediatrics; University of Turin; Turin Italy
9. Department of Public Health; Experimental and Forensic Medicine; University of Pavia; Pavia Italy