Outcomes of influenza A(H1N1)pdm09 virus infection: results from two international cohort studies

Lynfield, Ruth, Davey, Richard, Dwyer, Dominic E., Losso, Marcelo H., Wentworth, Deborah, Cozzi-Lepri, Alessandro, Herman-Lamin, Kathy, Cholewinska, Grazyna, David, Daniel, Kuetter, Stefan, Ternesgen, Zelalem, Uyeki, Timothy M., Lane, H. Clifford, Lundgren, Jens, Neaton, James D., INSIGHT Influenza Study Group and Emery, Sean (2014) Outcomes of influenza A(H1N1)pdm09 virus infection: results from two international cohort studies. PloS One, 9 7: . doi:10.1371/journal.pone.0101785

Author Lynfield, Ruth
Davey, Richard
Dwyer, Dominic E.
Losso, Marcelo H.
Wentworth, Deborah
Cozzi-Lepri, Alessandro
Herman-Lamin, Kathy
Cholewinska, Grazyna
David, Daniel
Kuetter, Stefan
Ternesgen, Zelalem
Uyeki, Timothy M.
Lane, H. Clifford
Lundgren, Jens
Neaton, James D.
INSIGHT Influenza Study Group
Emery, Sean
Title Outcomes of influenza A(H1N1)pdm09 virus infection: results from two international cohort studies
Journal name PloS One   Check publisher's open access policy
ISSN 1932-6203
Publication date 2014-07-08
Year available 2014
Sub-type Article (original research)
DOI 10.1371/journal.pone.0101785
Open Access Status DOI
Volume 9
Issue 7
Total pages 15
Place of publication San Francisco, CA, United States
Publisher Public Library of Science
Language eng
Formatted abstract

Data from prospectively planned cohort studies on risk of major clinical outcomes and prognostic factors for patients with influenza A(H1N1)pdm09 virus are limited. In 2009, in order to assess outcomes and evaluate risk factors for progression of illness, two cohort studies were initiated: FLU 002 in outpatients and FLU 003 in hospitalized patients.

Methods and Findings

Between October 2009 and December 2012, adults with influenza-like illness (ILI) were enrolled; outpatients were followed for 14 days and inpatients for 60 days. Disease progression was defined as hospitalization and/or death for outpatients, and hospitalization for >28 days, transfer to intensive care unit (ICU) if enrolled from general ward, and/or death for inpatients. Infection was confirmed by RT-PCR. 590 FLU 002 and 392 FLU 003 patients with influenza A (H1N1)pdm09 were enrolled from 81 sites in 17 countries at 2 days (IQR 1–3) and 6 days (IQR 4–10) following ILI onset, respectively. Disease progression was experienced by 29 (1 death) outpatients (5.1%; 95% CI: 3.4–7.2%) and 80 inpatients [death (32), hospitalization >28 days (43) or ICU transfer (20)] (21.6%; 95% CI: 17.5–26.2%). Disease progression (death) for hospitalized patients was 53.1% (26.6%) and 12.8% (3.8%), respectively, for those enrolled in the ICU and general ward. In pooled analyses for both studies, predictors of disease progression were age, longer duration of symptoms at enrollment and immunosuppression. Patients hospitalized during the pandemic period had a poorer prognosis than in subsequent seasons.


Patients with influenza A(H1N1)pdm09, particularly when requiring hospital admission, are at high risk for disease progression, especially if they are older, immunodeficient, or admitted late in infection. These data reinforce the need for international trials of novel treatment strategies for influenza infection and serve as a reminder of the need to monitor the severity of seasonal and pandemic influenza epidemics globally.
Keyword Multidisciplinary Sciences
Science & Technology - Other Topics
Q-Index Code C1
Q-Index Status Provisional Code
Grant ID HHSN261200800001E
Institutional Status Non-UQ
Additional Notes Article number e101785

Document type: Journal Article
Sub-type: Article (original research)
Collection: Faculty of Medicine
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Citation counts: TR Web of Science Citation Count  Cited 11 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 12 times in Scopus Article | Citations
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