Background: The severe forms of influenza infection requiring intensive care unit (ICU) admission remain a medical challenge due to its high mortality. New H1N1 strains were hypothesized to increase mortality. The studies below represent a large series focusing on ICU-admitted influenza patients over the last decade with an emphasis on factors related to death.

Methods: A retrospective study of patients admitted in ICU for influenza infection over the 2010-2019 period in Réunion Island (a French overseas territory) was conducted. Demographic data, underlying conditions, and therapeutic management were recorded. A univariate analysis was performed to assess factors related to ICU mortality.

Results: Three hundred and fifty adult patients were analyzed. Overall mortality was 25.1%. Factors related to higher mortality were found to be patient age >65, cancer history, need for intubation, early intubation within 48 h after admission, invasive mechanical ventilation (MV), acute respiratory distress syndrome (ARDS), vaso-support drugs, extracorporal oxygenation by membrane (ECMO), dialysis, bacterial coinfection, leucopenia, anemia, and thrombopenia. History of asthma and oseltamivir therapy were correlated with a lower mortality. H1N1 did not impact mortality.

Conclusion: Patient´s underlying conditions influence hospital admission and secondary ICU admission but were not found to impact ICU mortality except in patients age >65, history of cancer, and bacterial coinfections. Pulmonary involvement was often present, required MV, and often evolved toward ARDS. ICU mortality was strongly related to ARDS severity. We recommend rapid ICU admission of patients with influenza-related pneumonia, management of bacterial coinfection, and early administration of oseltamivir.