1. Division of Pediatric Hematology and Oncology, Oulu University Hospital, Oulu, Finland
2. University of Helsinki, Helsinki, Finland;
3. Division of Hematology-Oncology and Stem Cell Transplantation, New Children's Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
4. HUS Diagnostic Center, HUSLAB, Clinical Microbiology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
5. Department of Virology and Immunology, Helsinki University Hospital and University of Helsinki, Helsinki, Finland