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
. 2022 Jul 1;17(7):e0270740.
doi: 10.1371/journal.pone.0270740. eCollection 2022.

Does knowing the influenza epidemic threshold has been reached influence the performance of influenza case definitions?

Núria Soldevila  1   2 , Diana Toledo  1   2 , Ana Martínez  1   3 , Pere Godoy  1   3 , Núria Torner  1 , Cristina Rius  1   4 , Mireia Jané  1   2   3 , Angela Domínguez  1   2 ; PIDIRAC Sentinel Surveillance Program of Catalonia
Affiliations

Does knowing the influenza epidemic threshold has been reached influence the performance of influenza case definitions?

Núria Soldevila et al. PLoS One. .

Abstract

Background: Disease surveillance using adequate case definitions is very important. The objective of the study was to compare the performance of influenza case definitions and influenza symptoms in the first two epidemic weeks with respect to other epidemic weeks.

Methods: We analysed cases of acute respiratory infection detected by the network of sentinel primary care physicians of Catalonia for 10 seasons. We calculated the diagnostic odds ratio (DOR) and 95% confidence intervals (CI) for the first two epidemic weeks and for other epidemic weeks.

Results: A total of 4,338 samples were collected in the epidemic weeks, of which 2,446 (56.4%) were positive for influenza. The most predictive case definition for laboratory-confirmed influenza was the WHO case definition for influenza-like illness (ILI) in the first two epidemic weeks (DOR 2.10; 95% CI 1.57-2.81) and in other epidemic weeks (DOR 2.31; 95% CI 1.96-2.72). The most predictive symptom was fever. After knowing that epidemic threshold had been reached, the DOR of the ILI WHO case definition in children aged <5 years and cough and fever in this group increased (190%, 170% and 213%, respectively).

Conclusions: During influenza epidemics, differences in the performance of the case definition and the discriminative ability of symptoms were found according to whether it was known that the epidemic threshold had been reached or not. This suggests that sentinel physicians are stricter in selecting samples to send to the laboratory from patients who present symptoms more specific to influenza after rather than before an influenza epidemic has been declared.

PubMed Disclaimer

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Number of samples collected and positive samples for influenza by season and week.
Fig 2
Fig 2. DOR of clinical manifestations for the first two epidemic weeks and rest of epidemic weeks by age group.
Fig 3
Fig 3. DOR of clinical manifestations for the first two epidemic weeks and rest of epidemic weeks by comorbidities.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

References

    1. Treanor JJ. Influenza Viruses, including avian influenza and swine influenza. In: Bennett JE, Dolin R, Blaser MJ, editors. Principles and Practice of Infectious Diseases. 9th ed. Philadelphia: Elsevier; 2020. pp. 2143–2168.
    1. WHO. Influenza (Seasonal) [cited 26 June 2021]. Available from: https://www.who.int/en/news-room/fact-sheets/detail/influenza-(seasonal)
    1. Bresee JS, Fry A, Sambhara S, Cox NJ. Inactivated influenza vaccines. In: Plotkin SA, Orenstein WA, Offit PA, Edwards KM, editors. Vaccines. 7th ed. Philadelphia: Saunders; 2008. pp. 456–488.
    1. Won M, Marques-Pita M, Louro C, Gonçalves-Sá J. Early and real-time detection of seasonal influenza onset. PLoS Comput Biol. 2017;13: e1005330. doi: 10.1371/journal.pcbi.1005330 - DOI - PMC - PubMed
    1. World Health Organization. WHO Surveillance Case Definitions for ILI and SARI. Geneva: WHO Press; 2014.

Publication types