1. Hematology Oncology Unit; 2nd Pediatric Department; Aristotle University of Thessaloniki; AHEPA Hospital; Thessaloniki Greece
2. Institute of Continuing Medical Education of Ioannina; Ioannina Greece
3. Infectious Disease Research Program; Center for Bone Marrow Transplantation and Department of Pediatric Hematology/Oncology; University Children's Hospital Münster; Münster Germany