title: Patients hospitalized with laboratory-confirmed influenza during the 2010-2011 influenza season: exploring disease severity by virus type and subtype.
abstract: BACKGROUND
  The 2010-2011 influenza season was dominated by influenza A(H3N2) virus, but influenza A(H1N1) pdm09 (pH1N1) and B viruses cocirculated. This provided an opportunity to explore within-season predictors of severity among hospitalized patients, avoiding biases associated with season-to-season differences in strain virulence, population immunity, and healthcare seeking.
  
  
  METHODS
  Population-based, laboratory-confirmed influenza hospitalization surveillance data were used to examine the association between virus type/subtype and outcomes in children and adults. Multivariable analysis explored virus type/subtype, prompt antiviral treatment, medical conditions, and age as predictors for severity (intensive care unit admission or death).
  
  
  RESULTS
  In children, pH1N1 (adjusted odds ratio [aOR], 2.19; 95% confidence interval [CI], 1.11-4.3), chronic metabolic disease (aOR, 5.23; 95% CI, 1.74-15.69), and neuromuscular disorder (aOR, 4.84; 95% CI, 2.02-11.58) were independently associated with severity. In adults, independent predictors were pH1N1 (aOR, 2.21; 95% CI, 1.66-2.94), chronic lung disease (aOR, 1.46, 95% CI, 1.12-1.89), and neuromuscular disorder (aOR, 1.68; 95% CI, 1.11-2.52).Antiviral treatment reduced the odds of severity among adults (aOR, 0.47; 95% CI, .33-.68).
  
  
  CONCLUSIONS
  During the 2010-2011 season, pH1N1 caused more severe disease than H3N2 or B in hospitalized patients. Underlying medical conditions increased severity despite virus strain. Antiviral treatment reduced severity among adults. Our findings underscore the importance of influenza prevention.
authors.affiliation: Centers for Disease Control and Prevention.
authors.forename: Sandra S
authors.initials: SS
authors.lastname: Chaves
authors.forename: Deborah
authors.initials: D
authors.lastname: Aragon
authors.forename: Nancy
authors.initials: N
authors.lastname: Bennett
authors.forename: Tara
authors.initials: T
authors.lastname: Cooper
authors.forename: Tiffany
authors.initials: T
authors.lastname: D'Mello
authors.forename: Monica
authors.initials: M
authors.lastname: Farley
authors.forename: Brian
authors.initials: B
authors.lastname: Fowler
authors.forename: Emily
authors.initials: E
authors.lastname: Hancock
authors.forename: Pam Daily
authors.initials: PD
authors.lastname: Kirley
authors.forename: Ruth
authors.initials: R
authors.lastname: Lynfield
authors.forename: Patricia
authors.initials: P
authors.lastname: Ryan
authors.forename: William
authors.initials: W
authors.lastname: Schaffner
authors.forename: Ruta
authors.initials: R
authors.lastname: Sharangpani
authors.forename: Leslie
authors.initials: L
authors.lastname: Tengelsen
authors.forename: Ann
authors.initials: A
authors.lastname: Thomas
authors.forename: Diana
authors.initials: D
authors.lastname: Thurston
authors.forename: Jean
authors.initials: J
authors.lastname: Williams
authors.forename: Kimberly
authors.initials: K
authors.lastname: Yousey-Hindes
authors.forename: Shelley
authors.initials: S
authors.lastname: Zansky
authors.forename: Lyn
authors.initials: L
authors.lastname: Finelli
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003422:Critical Care; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000302:isolation & purification; D053122:Influenza A Virus, H3N2 Subtype / Q000145:classification / Q000302:isolation & purification; D009981:Influenza B virus / Q000145:classification / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology* / Q000401:mortality / Q000628:therapy / Q000821:virology; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D009975:Orthomyxoviridae / Q000145:classification* / Q000302:isolation & purification; D062486:Public Health Surveillance; D012121:Respiration, Artificial; D014481:United States / Q000453:epidemiology
keywords: influenza; influenza A(H1N1) pdm09; influenza hospitalizations; influenza surveillance; severe influenza