1. A Neonatal Department, “Aghia Sophia” Children's Hospital, Thivon and Levadias, 11527 Athens.
2. Department of Hygiene and Epidemiology, University of Athens Medical School, Mikras Asias 75, Goudi, 11527 Athens.
3. First Paediatric Clinic of Athens University, “Aghia Sophia” Children's Hospital, Thivon and Levadias, 11527 Athens.
4. Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA