Patients hospitalized with laboratory-confirmed influenza during the 2010-2011 influenza season: exploring disease severity by virus type and subtype

J Infect Dis. 2013 Oct 15;208(8):1305-14. doi: 10.1093/infdis/jit316. Epub 2013 Jul 17.

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.

Keywords: influenza; influenza A(H1N1) pdm09; influenza hospitalizations; influenza surveillance; severe influenza.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Child
  • Child, Preschool
  • Critical Care
  • Female
  • Hospitalization / statistics & numerical data
  • Humans
  • Infant
  • Influenza A Virus, H1N1 Subtype / classification
  • Influenza A Virus, H1N1 Subtype / isolation & purification
  • Influenza A Virus, H3N2 Subtype / classification
  • Influenza A Virus, H3N2 Subtype / isolation & purification
  • Influenza B virus / classification
  • Influenza B virus / isolation & purification
  • Influenza, Human / epidemiology*
  • Influenza, Human / mortality
  • Influenza, Human / therapy
  • Influenza, Human / virology
  • Male
  • Middle Aged
  • Odds Ratio
  • Orthomyxoviridae / classification*
  • Orthomyxoviridae / isolation & purification
  • Public Health Surveillance
  • Respiration, Artificial
  • United States / epidemiology