1. Regional Cystic Fibrosis Center of Tuscany, Division of Paediatric Infectious Diseases, Meyer Pediatric Hospital, Department of Pediatrics, University of Florence, Florence, Italy
2. Neonatal Intensive Care Unit, Meyer Pediatric Hospital, Department of Pediatrics, University of Florence, Florence, Italy
3. Department of Statistics ‘G. Parenti’, University of Florence, Florence, Italy