[1] Univ Milan, Dept Maternal & Pediat Sci, Fdn IRCCS Ca Granda Osped Maggiore Policlin, I-20122 Milan, Italy
[2] Fdn IRCCS Ca Granda Osped Maggiore Policlin, Pediat Radiol Unit, Milan, Italy
[3] Ist Ric Farmacol Mario Negri, Dept Epidemiol, Milan, Italy
[4] Fdn IRCCS Policlin San Matteo, Mol Virol Unit, Pavia, Italy