European Respiratory Society

Influenza pneumonia: a comparison between seasonal influenza virus and the H1N1 pandemic

R. Riquelme, A. Torres, M.L. Rioseco, S. Ewig, C. Cillóniz, M. Riquelme, C. Inzunza, E. Polverino, Y. Gomez, M.A. Marcos, C. Contreras, A. Gabarrús, R. Fasce


We compared clinical presentation, complications and outcome in patients with influenza A (H1N1) and seasonal influenza pneumonia.

The group of patients with influenza A (H1N1) pneumonia consisted of 75 patients. 52 patients with pneumonia associated with seasonal influenza were included for comparison.

Patients with pneumonia associated with novel H1N1 influenza were younger (mean age 39.7 yrs versus 69.6 yrs) and had fewer chronic comorbidities and less alcoholism. Infiltrates were more extensive and frequently interstitial. Respiratory failure was more frequent (those with an arterial oxygen tension/inspiratory oxygen fraction ratio <200 28% versus 12%, p = 0.042), leading to a higher rate of intensive care unit (ICU) admission and mechanical ventilation (29.3% versus 7.7% (p<0.0030) and 18.7% versus 2% (p<0.0045)). Mortality was twice as high in patients with novel H1N1 (12% versus 5.8%; p = 0.238), although this was not significant, and was attributable to pneumonia in most instances (77.8% versus 0%; p = 0.046).

Younger age, fewer comorbidities, more extensive radiographic extension and more severe respiratory compromise, and ICU admissions are key features of the clinical presentation of patients with novel H1N1-associated pneumonia compared with seasonal influenza pneumonia.


  • Support Statement

    This study has been supported in part by grant number 2009 SGR 911 from Ciber de Enfermedades Respiratorias (Ciberes CB06/06/0028). Ciberes is an initiative of the Instituto de Salud Carlos III.

  • Statement of Interest

    Statements of interest for A. Torres and S. Ewig can be found at

  • Received August 6, 2010.
  • Accepted October 18, 2010.
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