title: A comparison of H1N1 influenza among pediatric inpatients in the pandemic and post pandemic era.
abstract: BACKGROUND
  The novel influenza A H1N1 (A[H1N1]pdm09) strain emerged in 2009, contributing to significant morbidity and mortality. It is not known whether illness associated with A(H1N1) pdm09 in the post-pandemic era exhibits a similar disease profile.
  
  
  OBJECTIVE
  The objectives of this study were to compare the burden of disease of A(H1N1) pdm09 influenza from the 2009 pandemic year to the post-pandemic years (2010-2014), and to explore potential reasons for any differences.
  
  
  METHODS
  We conducted a retrospective cohort study of inpatients admitted to Children's Hospital Colorado with a positive respiratory specimen for influenza from May-December, 2009 and December, 2010-April, 2014. Univariate and multivariate analyses were conducted to compare the demographics and clinical characteristics of patients with H1N1 during the two periods.
  
  
  RESULTS
  There were 388 inpatients with influenza A(H1N1) pdm09 in 2009, and 117 during the post-pandemic years. Ninety-four percent of all H1N1 during the post-pandemic era was observed during the 2013-2014 influenza season. Patients with A(H1N1) pdm09 during the post-pandemic year were less likely to have an underlying medical condition (P<0.01). Patients admitted to the ICU during the post-pandemic year had a lower median age (5 vs 8 years, P=0.01) and a lower proportion of patients were intubated, had mental status changes, and ARDS compared with the pandemic years, (P<0.01 for all), with decreased mortality (P=0.02).
  
  
  CONCLUSIONS
  Patients with influenza A(H1N1) pdm09 during the post-pandemic years appeared to have less severe disease than patients with A(H1N1) pdm09 during the pandemic year. The reasons for this difference are likely multifactorial.
authors.affiliation: Department of Pediatrics (Hospital Medicine and Infectious Diseases), University of Colorado School of Medicine and Children's Hospital Colorado, Aurora, CO, USA. Electronic address: suchitra.rao@childrenscolorado.org.
authors.forename: Suchitra
authors.initials: S
authors.lastname: Rao
authors.affiliation: University of Colorado School of Medicine, Adult and Child Center for Health Outcomes Research and Delivery Science, Aurora, CO, USA.
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Torok
authors.affiliation: Department of Pediatrics, University of Maryland School of Medicine, MD, USA.
authors.forename: Dayanand
authors.initials: D
authors.lastname: Bagdure
authors.affiliation: Department of Pediatrics (Hospital Medicine), University of Colorado School of Medicine and Children's Hospital Colorado, Aurora, CO, USA.
authors.forename: Maureen A
authors.initials: MA
authors.lastname: Cunningham
authors.affiliation: Department of Pediatrics, University of Colorado School of Medicine and Children's Hospital Colorado, Aurora, CO, USA.
authors.forename: Joshua T B
authors.initials: JT
authors.lastname: Williams
authors.affiliation: Department of Pediatrics (Infectious Diseases), University of Colorado School Of Medicine and Children's Hospital Colorado, Aurora, CO, USA.
authors.forename: Donna J
authors.initials: DJ
authors.lastname: Curtis
authors.affiliation: Department of Pediatrics (Hospital Medicine), University of Colorado School of Medicine and Children's Hospital Colorado, Aurora, CO, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Wilson
authors.affiliation: Department of Pediatrics (Infectious Diseases), University of Colorado School Of Medicine and Children's Hospital Colorado, Aurora, CO, USA.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Dominguez
mesh_terms: D002648:Child; D002675:Child, Preschool; D003120:Colorado / Q000453:epidemiology; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology / Q000473:pathology* / Q000821:virology*; D007297:Inpatients; D008297:Male; D012189:Retrospective Studies; D013997:Time Factors
keywords: H1N1; Influenza; Inpatients; Pandemic; Post-pandemic period