- Correspondence to Dr Marina Cuttini, Unit of Epidemiology, Bambino Gesù Children's Hospital, Viale Ferdinando Baldelli 41, Roma 00146, Italy;
- Received 22 August 2013
- Accepted 26 August 2013
- Published in print 1 December 2013.
- Published online 5 November 2013.
- Published first 19 September 2013.
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