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H1N1: viral pneumonia as a cause of acute respiratory distress syndrome

Ramsey, Clarea,b,c; Kumar, Anandb

Current Opinion in Critical Care: February 2011 - Volume 17 - Issue 1 - p 64–71
doi: 10.1097/MCC.0b013e3283427259
Respiratory system: Edited by Antonio Pesenti

Purpose of review To review the literature on novel swine origin influenza A (H1N1 2009) as a cause of respiratory failure and acute respiratory distress syndrome (ARDS).

Recent findings H1N1 2009 was first recognized as a pathogen in March of 2009, when there was a spike in the number of cases of influenza-like illness leading to severe and at times fatal pneumonia. The etiologic agent was then identified as a novel H1N1 influenza A virus, which subsequent spread rapidly throughout the globe. Most countries reported cases of severe viral pneumonitis requiring intensive care unit (ICU) admission. Severe disease was noted to occur more commonly in younger patients than those typically affected by seasonal influenza and obesity and pregnancy were associated with severe disease. The majority of patients requiring ICU admission met criteria for ARDS and case fatality ratio was estimated at less than 0.5%. Chest radiographs and pathology resembled ARDS and most patients were treated with low tidal volume ventilation, high positive end expiratory pressure and at times, rescue therapies. Available evidence suggests that early antiviral treatment improves outcomes from H1N1 2009.

Summary H1N1 2009 has emerged as an important cause of ARDS in 2009–2010. Prompt recognition and treatment with antivirals improves outcomes.

aSection of Respiratory Medicine, Department of Medicine, University of Manitoba, Canada

bSection of Critical Care, Department of Medicine, University of Manitoba, Canada

cDepartment of Community Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada

Correspondence to Clare Ramsey, MD, MSc, FRCPC, RS 309, 810 Sherbrook St, Winnipeg, MB R3A 1R8, Canada Fax: +1 204 787 1087; e-mail:

© 2011 Lippincott Williams & Wilkins, Inc.