1. Respiratory Diseases Clinic, and
2. Unit of Biostatistics, Epidemiology and Public Health, Department of Cardiac, Thoracic, Vascular Sciences and Public Health, and
3. Environmental Protection and Prevention Agency of the Veneto Region, Venezia, Italy; and
4. Meakins-Christie Laboratories Respiratory Division, McGill University, Montreal, Quebec, Canada
5. Department of Woman and Child Health, University of Padova, Padova, Italy;