1. Lund University, Skane University Hospital; Department of Paediatrics; Lund Sweden
2. Health Regional Agency of the Liguria Region; Genoa Italy
3. University of Milan; Department of Biomedical Sciences for Health; Via Pascal 36 Milan Italy 20133
4. IRCCS Galeazzi Orthopaedic Institute; Clinical Epidemiology Unit; Milan Italy
5. Istituto Giannina Gaslini; Epidemiology, Biostatistics and Committees Unit; Genoa Italy 16147