Comparison of the outcomes of individuals with medically attended influenza a and b virus infections enrolled in 2 international cohort studies over a 6-year period: 2009-2015

Dominic E. Dwyer, Ruth Lynfield, Marcelo H. Losso, Richard T. Davey, Alessandro Cozzi-Lepri, Deborah Wentworth, Timothy M. Uyeki, Fred Gordin, Brian Angus, Tavs Qvist, Sean Emery, Jens Lundgren, James D. Neaton

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Background. Outcome data from prospective follow-up studies comparing infections with different influenza virus types/subtypes are limited. Methods. Demographic, clinical characteristics and follow-up outcomes for adults with laboratory-confirmed influenza A(H1N1)pdm09, A(H3N2), or B virus infections were compared in 2 prospective cohorts enrolled globally from 2009 through 2015. Logistic regression was used to compare outcomes among influenza virus type/subtypes. Results. Of 3952 outpatients, 1290 (32.6%) had A(H1N1)pdm09 virus infection, 1857 (47.0%) had A(H3N2), and 805 (20.4%) had influenza B. Of 1398 inpatients, 641 (45.8%) had A(H1N1)pdm09, 532 (38.1%) had A(H3N2), and 225 (16.1%) had influenza B. Outpatients with A(H1N1)pdm09 were younger with fewer comorbidities and were more likely to be hospitalized during the 14-day follow-up (3.3%) than influenza B (2.2%) or A(H3N2) (0.7%; P < .0001). Hospitalized patients with A(H1N1)pdm09 (20.3%) were more likely to be enrolled from intensive care units (ICUs) than those with A(H3N2) (11.3%) or B (9.8%; P < .0001). However, 60-day follow-up of discharged inpatients showed no difference in disease progression (P = .32) or all-cause mortality (P = .30) among influenza types/subtypes. These findings were consistent after covariate adjustment, in sensitivity analyses, and for subgroups defined by age, enrollment location, and comorbidities. Conclusions. Outpatients infected with influenza A(H1N1)pdm09 or influenza B were more likely to be hospitalized than those with A(H3N2). Hospitalized patients infected with A(H1N1)pdm09 were younger and more likely to have severe disease at study entry (measured by ICU enrollment), but did not have worse 60-day outcomes.

Original languageEnglish (US)
Article numberofx212
JournalOpen Forum Infectious Diseases
Issue number4
StatePublished - 2020

Bibliographical note

Funding Information:
Financial support. This work, through the INSIGHT Network, was funded by National Institutes of Health Grant UOI-AI068641. The FLU002 and FLU003 studies were partially funded by the National Cancer Institute, National Institutes of Health, under Contract No. HHSN261200800001E. The funding sources had no role in the collection, analysis, or interpretation of data; the writing of the report; or the decision to submit the paper for publication. The content of this publication does not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the US Government.

Publisher Copyright:
© The Author(s) 2017.


  • Follow-up
  • Influenza A(H1N1)pdm09
  • Influenza A(H3N2)
  • Influenza B
  • Outcomes


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