title: Clinical features of infants hospitalized for 2009 pandemic influenza A (H1N1) in Japan: analysis using a national hospital discharge database.
abstract: BACKGROUND
  Earlier studies reported that infants <12 months of age were at high risk of hospitalization for 2009 pandemic influenza A H1N1 virus (2009 H1N1) infection, but there was little information about the clinical courses in these patients.
  
  
  METHODS
  A retrospective study was performed using the nationwide inpatient Diagnosis Procedure Combination Database in Japan. We searched data on hospitalizations, between July and December 2009, of infants (<12 months) and children 12 to <24 months of age with influenza. We examined their demographic data and hospitalization details, including treatment, complications, and outcomes.
  
  
  RESULTS
  During the study period, 1023 infants were hospitalized for influenza; 98.1% of them were previously healthy. Complications attributed to influenza were found in 181 (17.7%) infants, including 3 critical illnesses and 1 death. Oseltamivir was prescribed to 535 (53.3%) infants. We found no evidence that oseltamivir was associated with either complications or length of hospital stay. During the same period, 579 children 1 year of age were admitted for 2009 H1N1, and 56.5% of them had influenza-related complications.
  
  
  CONCLUSIONS
  In Japan, infants with 2009 H1N1 were twice as likely to be hospitalized as children 1 year of age. However, the clinical course of the hospitalized infants was generally uncomplicated.
authors.affiliation: Department of Pediatrics, The University of Tokyo Hospital, Tokyo, Japan. masatotakeuchi@gmail.com
authors.forename: Masato
authors.initials: M
authors.lastname: Takeuchi
authors.forename: Hideo
authors.initials: H
authors.lastname: Yasunaga
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Horiguchi
authors.forename: Shinya
authors.initials: S
authors.lastname: Matsuda
mesh_terms: D000367:Age Factors; D000998:Antiviral Agents / Q000008:administration & dosage; D005260:Female; D006776:Hospitals, Pediatric; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification* / Q000472:pathogenicity*; D007251:Influenza, Human / Q000453:epidemiology* / Q000473:pathology* / Q000821:virology; D007564:Japan / Q000453:epidemiology; D008297:Male; D053139:Oseltamivir / Q000008:administration & dosage; D058873:Pandemics; D012189:Retrospective Studies; D016896:Treatment Outcome
chemical_list: D000998:Antiviral Agents; D053139:Oseltamivir