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Review
. 2021 Sep;26(39):2000343.
doi: 10.2807/1560-7917.ES.2021.26.39.2000343.

Spotlight influenza: Laboratory-confirmed seasonal influenza in people with acute respiratory illness: a literature review and meta-analysis, WHO European Region, 2004 to 2017

Sara Belazi  1 , Sonja J Olsen  2 , Caroline Brown  2 , Helen K Green  3 , Piers Mook  2 , Jonathan Nguyen-Van-Tam  1 , Pasi Penttinen  4 , Louise Lansbury  1
Affiliations
Review

Spotlight influenza: Laboratory-confirmed seasonal influenza in people with acute respiratory illness: a literature review and meta-analysis, WHO European Region, 2004 to 2017

Sara Belazi et al. Euro Surveill. 2021 Sep.

Abstract

BackgroundAcross the World Health Organization European Region, there are few estimates of the proportion of people seeking medical care for influenza-like illness or acute respiratory infections and who have laboratory-confirmed seasonal influenza infection.MethodsWe conducted a meta-analysis of data extracted from studies published between 2004 and 2017 and from sentinel data from the European surveillance system (TESSy) between 2004 and 2018. We pooled within-season estimates by influenza type/subtype, setting (outpatient (OP)/inpatient (IP)) and age group to estimate the proportion of people tested who have laboratory-confirmed and medically-attended seasonal influenza in Europe.ResultsIn the literature review, the pooled proportion for all influenza types was 33% (95% confidence interval (CI): 30-36), higher among OP 36% (95% CI: 33-40) than IP 24% (95% CI: 20-29). Pooled estimates for all influenza types by age group were: 0-17 years, 26% (22-31); 18-64 years, 41% (32-50); ≥ 65 years, 33% (27-40). From TESSy data, 33% (31-34) of OP and 24% (21-27) of IP were positive. The highest proportion of influenza A was in people aged 18-64 years (22%, 16-29). By subtype, A(H1N1)pdm09 was highest in 18-64 year-olds (16%, 11-21%) whereas A(H3N2) was highest in those ≥ 65 years (10%, 2-22). For influenza B, the highest proportion of infections was in those aged 18-64 years (15%, 9-24).ConclusionsLaboratory-confirmed influenza accounted for approximately one third of all acute respiratory infections for which medical care was sought during the influenza season.

Keywords: acute respiratory infection; influenza A virus; influenza B virus; influenza human; influenza-like illness; medically-attended.

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Conflict of interest statement

Conflict of interest: JSN-V-T is currently seconded to the Department of Health and Social Care (DHSC), England, UK. All other authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1
PRISMA flowchart displaying number of articles identified and screened at each stage of the literature review (n =  9,461)
Figure 2
Figure 2
Forest plot of studies from literature review showing proportion of all influenza viruses grouped by healthcare setting, WHO Europe Region, 2004–2017 (n = 145,057)
Figure 3
Figure 3
Influenza positivity as a proportion of all ARI/ILI tested by influenza season: all influenza and by type and subtype (TESSy data)
See this image and copyright information in PMC

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