Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Meta-Analysis
. 2013 Aug 23:347:f5061.
doi: 10.1136/bmj.f5061.

Populations at risk for severe or complicated influenza illness: systematic review and meta-analysis

Dominik Mertz  1 , Tae Hyong Kim, Jennie Johnstone, Po-Po Lam, Michelle Science, Stefan P Kuster, Shaza A Fadel, Dat Tran, Eduardo Fernandez, Neera Bhatnagar, Mark Loeb
Affiliations
Meta-Analysis

Populations at risk for severe or complicated influenza illness: systematic review and meta-analysis

Dominik Mertz et al. BMJ. .

Abstract

Objective: To evaluate risk factors for severe outcomes in patients with seasonal and pandemic influenza.

Design: Systematic review.

Study selection: Observational studies reporting on risk factor-outcome combinations of interest in participants with influenza. Outcomes included death, ventilator support, admission to hospital, admission to an intensive care unit, pneumonia, and composite outcomes.

Data sources: Medline, Embase, CINAHL, Global Health, and the Cochrane Central Register of Controlled Trials to March 2011.

Risk of bias assessment: Newcastle-Ottawa scale to assess the risk of bias. GRADE framework to evaluate the quality of evidence.

Results: 63 537 articles were identified of which 234 with a total of 610 782 participants met the inclusion criteria. The evidence supporting risk factors for severe outcomes of influenza ranged from being limited to absent. This was particularly relevant for the relative lack of data for non-2009 H1N1 pandemics and for seasonal influenza studies. Limitations in the published literature included lack of power and lack of adjustment for confounders was widespread: adjusted risk estimates were provided for only 5% of risk factor-outcome comparisons in 39 of 260 (15%) studies. The level of evidence was low for "any risk factor" (odds ratio for mortality 2.77, 95% confidence interval 1.90 to 4.05 for pandemic influenza and 2.04, 1.74 to 2.39 for seasonal influenza), obesity (2.74, 1.56 to 4.80 and 30.1, 1.74 to 2.39), cardiovascular diseases (2.92, 1.76 to 4.86 and 1.97, 1.06 to 3.67), and neuromuscular disease (2.68, 1.91 to 3.75 and 3.21, 1.84 to 5.58). The level of evidence was very low for all other risk factors. Some well accepted risk factors such as pregnancy and belonging to an ethnic minority group could not be identified as risk factors. In contrast, women who were less than four weeks post partum had a significantly increased risk of death from pandemic influenza (4.43, 1.24 to 15.81).

Conclusion: The level of evidence to support risk factors for influenza related complications is low and some well accepted risk factors, including pregnancy and ethnicity, could not be confirmed as risks. Rigorous and adequately powered studies are needed.

PubMed Disclaimer

Conflict of interest statement

Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare that: DM was partly supported by a research scholarship from the Swiss National Science Foundation (PASMP3-132571) and the Lichtenstein-Stiftung and is a recipient of a research early career award from Hamilton Health Sciences Foundation (Jack Hirsh Fellowship); ML holds the Michael G DeGroote chair in infectious diseases at McMaster University; JJ receives salary support from the Canadian Institutes of Health Research; ML has been a paid consultant for GlaxoSmithKline, Novartis, and Sanofi Pasteur (vaccine manufacturers); all other authors have no relationships with companies that might have an interest in the submitted work in the previous three years; spouses, partners, or children of the authors have no financial relationship that may be relevant to the submitted work; all authors have no non-financial interests that may be relevant to the submitted work.

Figures

None
Flow of studies included and excluded
See this image and copyright information in PMC

Comment in

References

    1. World Health Organization. Fact sheet on influenza. 2009. www.who.int/mediacentre/factsheets/fs211/en/index.html.
    1. Center for Disease Control and Prevention. People at high risk of developing flu-related complications. 2012. www.cdc.gov/flu/index.htm.
    1. Dawood FS, Iuliano AD, Reed C, Meltzer MI, Shay DK, Cheng PY, et al. Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modelling study. Lancet Infect Dis 2012;12:687-95. - PubMed
    1. Fiore AE, Uyeki TM, Broder K, Finelli L, Euler GL, Singleton JA, et al. Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2010. MMWR Recomm Rep 2010;59(RR-8):1-62. - PubMed
    1. World Health Organization. Strategic Advisory Group of Experts (SAGE) meeting of April 2012. www.who.int/influenza/vaccines/SAGE_information/en/index.html.

MeSH terms

Substances