1. Department of Pediatrics; Medical Center Leeuwarden; P.O. Box 888 8901 BR Leeuwarden The Netherlands
2. Center for Medical Microbiology and Infectious Diseases; Izore; Leeuwarden The Netherlands
3. Department of Epidemiology; University Medical Center Groningen; The Netherlands
4. Department of Pediatric Intensive Care, Wilhelmina Children's Hospital; University Medical Center Utrecht; The Netherlands
5. Department of Pediatrics and Infectious Diseases, Wilhelmina Children's Hospital; University Medical Center Utrecht; The Netherlands