Does Knowing the Influenza Epidemic Threshold Has Been Reached Influence the Performance of Influenza Case Definitions?

Overview

Journal PLoS One

Specialties General Medicine
Science

Date 2022 Jul 1

PMID 35776716

Authors

Nuria Soldevila

Diana Toledo

Ana Martinez

Pere Godoy

Nuria Torner

Cristina Rius

Mireia Jane

Angela Dominguez

Affiliations

Soon will be listed here.

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.

Citing Articles

SARS-CoV-2, influenza A/B and respiratory syncytial virus positivity and association with influenza-like illness and self-reported symptoms, over the 2022/23 winter season in the UK: a longitudinal surveillance cohort.

Dietz E, Pritchard E, Pouwels K, Ehsaan M, Blake J, Gaughan C BMC Med. 2024; 22(1):143.

PMID: 38532381 PMC: 10964495. DOI: 10.1186/s12916-024-03351-w.

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