1 Willem-Alexander Children's Hospital, Department of Pediatrics, Division of Pediatric Immunology and Stem Cell Transplantation, Leiden University Medical Center, Albinusdreef 2, 2333 ZA, Leiden, the Netherlands.
2 Department of Pediatric Infectious Diseases and Immunology, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, the Netherlands.
3 Willem-Alexander Children's Hospital, Department of Pediatrics, Division of Pediatric Immunology and Stem Cell Transplantation, Leiden University Medical Center, Albinusdreef 2, 2333 ZA, Leiden, the Netherlands. d.berghuis@lumc.nl.