Original StudiesNationwide Study on the Course of Influenza A (H1N1) Infections in Hospitalized Children in the Netherlands During the Pandemic 2009–2010Ahout, Inge M. L. MD, PhD*; Philipsen, Ria L. A. Bsc*; Las, Mariëtte Bsc*,†; Baysan, Meryem MD*; Brus, Frank MD, PhD‡; Rahamat-Langendoen, Jeanette C. MD, PhD§; Roeleveld, Nel MD, PhD*,¶; Fraaij, Pieter L. MD, PhD‖,**; Osterhaus, Albert D. M. E. MD††,‡‡; Ferwerda, Gerben MD, PhD*; de Groot, Ronald MD, PhD*; for the Dutch H1N1 Research GroupAuthor Information From the *Department of Pediatrics, Laboratory of Pediatric Infectious Diseases, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands †Paediatric Drug Research Centre Nijmegen, Radboudumc Amalia Children’s Hospital, Radboud University Medical Center, Nijmegen, The Netherlands ‡Juliana Childrens Hospital, Haga Teaching Hospital, The Hague, The Netherlands §Department of Medical Microbiology, Radboud University Medical Center, Nijmegen, The Netherlands ¶Department for Health Evidence, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, The Netherlands ‖Department of Pediatrics, Sophia Childrens Hospital, Erasmus MC, Rotterdam, The Netherlands **Department of Viroscience, Erasmus MC, Rotterdam, The Netherlands ††Research Institute for Infectious Diseases and Zoonoses, Veterinary University Hannover, Germany ‡‡Artemis One Health Foundation, Utrecht, The Netherlands. Accepted for publication July 13, 2018. The authors have indicated they have no personal financial relationships relevant to this article to disclose. This study was supported by a personal grant to RdG from the Edgar Doncker Foundation. The authors have no conflicts of interest to disclose. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.pidj.com). Address for correspondence: Ronald de Groot, MD, PhD, Department of Pediatrics, Laboratory of Pediatric Infectious Diseases Route 412, Radboud University Medical Center, Philips van Leydenlaan 15, 6525 GA Nijmegen, The Netherlands. E-mail: Ronald.deGroot@radboudumc.nl. The Pediatric Infectious Disease Journal: December 2018 - Volume 37 - Issue 12 - p e283-e291 doi: 10.1097/INF.0000000000002177 Buy SDC Metrics Abstract Background: The influenza H1N1 pandemic of 2009–2010, provided a unique opportunity to assess the course of disease, as well as the analysis of risk factors for severe disease in hospitalized children (< 18 years). Methods: Retrospective national chart study on hospitalized children with H1N1 infection during the 2009–2010 pH1N1 outbreak. Results: Nine hundred forty patients (56% boys), median age 3.0 years, were enrolled; the majority were previously healthy. Treatment consisted of supplemental oxygen (24%), mechanical ventilation (5%) and antiviral therapy (63%). Fifteen patients died (1.6%), 5 of whom were previously healthy. Multivariable analyses confirmed pre-existent heart and lung disease as risk factors for intensive care unit admission. Risk factors for mortality included children with a neurologic or oncologic disease and psychomotor retardation. Conclusions: This nationwide overview of hospitalized children confirms known risk groups for severe influenza infections. However, most of the acute and severe presentations of influenza occurred in previously healthy children. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.