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Abstract

BACKGROUND

Portugal is establishing a surveillance system for severe acute respiratory infection (SARI). Data from its existing influenza surveillance system in intensive care units (ICU), operating since 2012, has not yet been analysed.

AIM

We aimed to identify individual and seasonal determinants of death from influenza in ICUs to inform ICU capacity planning, triage and SARI surveillance.

METHODS

We conducted a retrospective cohort study of laboratory-confirmed influenza cases admitted to 27 ICUs between 2012 and 2024. Covariates included demographics, comorbidities, season, influenza type, seasonal and weekly influenza caseload in the ICU and weekly ICU occupancy. We calculated case fatality rates and adjusted risk ratios (aRR) for death during ICU admission using log-binomial regression. Directed acyclic graphs informed model-specific adjustments, including age, sex, influenza type and comorbidities.

RESULTS

Of 1,071 cases with known outcome, 262 (24%) died. Case fatality rates were higher among patients with chronic liver disease (aRR: 2.0; 95% CI: 1.5–2.6), cancer (aRR: 1.6; 95% CI: 1.1–2.1) and during a high caseload season (aRR: 1.52; 95% CI: 1.16–2.05). Case fatality rates increased with age and were highest for those aged ≥80 years (aRR: 11; 95% CI: 2.4–184), compared with 0–19-year-olds.

CONCLUSION

Liver disease, cancer and older age were associated with increased fatality. Case fatality was higher in seasons with higher caseloads but showed no significant variation within seasons and did not increase during influenza peaks. These findings inform ICU triage and capacity planning for future seasons and support the implementation of broader SARI surveillance.

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This work is licensed under a Creative Commons Attribution 4.0 International License.
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/content/10.2807/1560-7917.ES.2026.31.8.2500505
2026-02-26
2026-03-15
/content/10.2807/1560-7917.ES.2026.31.8.2500505
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Individual and seasonal determinants of death among influenza patients in intensive care units: a retrospective cohort study, Portugal, 2012 to 2024
<p class="citation"> <span>Citation style for this article:</span> <span class="meta-value authors"> <a href="/search?value1=Sebastian+von+Schreeb&option1=author&noRedirect=true" class="nonDisambigAuthorLink">von Schreeb Sebastian</a>, <a href="/search?value1=Ana+Firme&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Firme Ana</a>, <a href="/search?value1=Mariana+Ferreira&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Ferreira Mariana</a>, <a href="/search?value1=Carina+Castro+Silva&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Castro Silva Carina</a>, <a href="/search?value1=Joana+Vidal-Castro&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Vidal-Castro Joana</a>, <a href="/search?value1=Eunice+das+Neves+Salgado+Cris%C3%B3stomo&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Crisóstomo Eunice das Neves Salgado</a>, <a href="/search?value1=Catarina+Filipa+Sousa+Marques&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Sousa Marques Catarina Filipa</a>, <a href="/search?value1=Hugo+Filipe+Baptista+Monteiro&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Monteiro Hugo Filipe Baptista</a>, <a href="/search?value1=Filipe+Froes&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Froes Filipe</a>, <a href="/search?value1=Rui+Pedro+Leit%C3%A3o&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Leitão Rui Pedro</a>, <a href="/search?value1=Kostas+Danis&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Danis Kostas</a>, <a href="/search?value1=Isabel+Marinho+Falc%C3%A3o&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Falcão Isabel Marinho</a>, <a href="/search?value1=Paula+Vasconcelos&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Vasconcelos Paula</a>, <a href="/search?value1=Vasco+Ricoca+Peixoto&option1=author&noRedirect=true" class="nonDisambigAuthorLink">Ricoca Peixoto Vasco</a></span>. Individual and seasonal determinants of death among influenza patients in intensive care units: a retrospective cohort study, Portugal, 2012 to 2024. <a href="/content/ecdc">Euro Surveill.</a> 2026;31(8):pii=2500505. <a href="https://doi.org/10.2807/1560-7917.ES.2026.31.8.2500505" title="doi link" target="_blank">https://doi.org/10.2807/1560-7917.ES.2026.31.8.2500505</a> <span class="ES_Article_citation"> <span class="generated">Received</span>: 09 Jul 2025;&nbsp;&nbsp; <span class="generated">Accepted</span>: 10 Nov 2025 </span> </p>
/content/10.2807/1560-7917.ES.2026.31.8.2500505
/content/10.2807/1560-7917.ES.2026.31.8.2500505
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