1 Department of Pediatric Infectious diseases and Immunology, Wilhelmina Children's Hospital, University Medical Center Utrecht, Utrecht 3584 EA, Netherlands; Department of Pediatrics, St Antonius Hospital, Nieuwegein, Netherlands. Electronic address: n.i.mazur@umcutrecht.nl.
2 Department of Pediatric Infectious diseases and Immunology, Wilhelmina Children's Hospital, University Medical Center Utrecht, Utrecht 3584 EA, Netherlands.