Assessing the Impact of SARS-CoV-2 on Influenza-Like Illness Surveillance Trends in the Community during the 2023/2024 Winter in England

Jonathon Mellor; Martyn Fyles; Robert S Paton; Alexander Phillips; Christopher E Overton; Thomas Ward

doi:10.1016/j.ijid.2024.107307

Assessing the Impact of SARS-CoV-2 on Influenza-Like Illness Surveillance Trends in the Community during the 2023/2024 Winter in England

Int J Infect Dis. 2024 Nov 16:107307. doi: 10.1016/j.ijid.2024.107307. Online ahead of print.

Authors

Jonathon Mellor¹, Martyn Fyles², Robert S Paton², Alexander Phillips³, Christopher E Overton⁴, Thomas Ward²

Affiliations

¹ UK Health Security Agency, 10 South Colonnade, Poplar, London, UK. Electronic address: Jonathon.mellor@ukhsa.gov.uk.
² UK Health Security Agency, 10 South Colonnade, Poplar, London, UK.
³ UK Health Security Agency, 10 South Colonnade, Poplar, London, UK; Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, UK.
⁴ UK Health Security Agency, 10 South Colonnade, Poplar, London, UK; Department of Mathematical Sciences, University of Liverpool, Liverpool, UK.

PMID: 39557283
DOI: 10.1016/j.ijid.2024.107307

Abstract

Background: Influenza-like-illness is a commonly used symptom categorisation in seasonal disease surveillance focusing on influenza in community and clinical settings. However, SARS-CoV-2 often causes presentation with a similar symptom profile. We explore how SARS-CoV-2 positive individuals can influence surveillance trends for WHO, CDC and ECDC influenza-like-illness criteria.

Methods: Harnessing the Winter COVID-19 Infection Study in England, a cohort study, the prevalence of different influenza-like-illness definitions are modelled using multilevel-regression and poststratification using age and spatial stratifications with temporal smoothing. Trends over time across stratifications were compared for SARS-CoV-2 positive and negative individuals to understand differences in influenza-like-illness trends. Symptom presentation across positive and negative SARS-CoV-2 cases were compared.

Results: SARS-CoV-2 symptom profiles are shown to overlap with the influenza-like-illness case definitions, particularly for "cough" and "fever", causing SARS-CoV-2 positive individuals to be frequently detected as influenza-like-illness cases. The trend of SARS-CoV-2 positives is a substantial component of the influenza-like-illness modelled trend driving an earlier perceived peak in prevalence. The ECDC symptom definition was most influenced by SARS-CoV-2 positive individuals.

Conclusion: Using a large community cohort we show how SARS-CoV-2 can impact influenza-like-illness surveillance trends. SARS-CoV-2 makes up a substantial part of the community influenza-like-illness burden and public health messaging should reflect this when discussing influenza-like-illness. We show influenza-like-illness is no longer a strong proxy for influenza activity alone.

Keywords: COVID-19; SARS-CoV-2; influenza; influenza-like-illness; syndromic surveillance.