1. Departament of Pediatrics, Division of Neonatology, Hospital de São João, Porto, Portugal
2. Faculty of Medicine of Porto University, Porto, Portugal
3. Division of Neonatology, Maternity Júlio Dinis, Porto Hospital Centre, Porto, Portugal
4. Centre of Histocompatibility of Porto, Porto, Portugal
5. Department of Hygiene and Epidemiology, Porto, Portugal