Tracking clinical severity of influenza in adult hospitalized patients in 2024: Data from the FluTer registry in Poland

Abstract

In late 2024, infectious disease specialists in Poland became alarmed about increased influenza-related hospitalizations, prompting concerns about disease severity shifts and underlying causes. Therefore, this retrospective study aimed to analyze the demographic and clinical characteristics of hospitalized influenza patients in 2024. Data were collected from thirteen infectious disease units participating in the FluTer registry. Hospitalization trends were compared with national surveillance data. Patient profiles, symptoms, laboratory results, and clinical severity were analyzed across early (2023/2024 epidemic season; January–August) and late 2024 (2024/2025 season; September–December), including sex-based differences. A total of 298 influenza-related hospitalizations were recorded in 2024, representing a 326 % increase from 2023, despite national surveillance reporting the lowest influenza incidence in three years. The majority (95.1 %) of cases were due to type A influenza, with 37.2 % of hospitalizations and 57.1 % of in-hospital deaths occurring in December 2024. Hospitalized patients were predominantly elderly, unvaccinated, obese, or had comorbidities. There were no significant differences in patient characteristics between the beginning and end of 2024, apart from a higher prevalence of peripheral vascular disease and asthma in later months. In-hospital mortality between September and December 2024 reached 6.1 %, peaking at 7.2 % in December. This was higher than the rates recorded in 2022 (1.7 %) and 2023 (5.1 %). Notably, all deaths in 2024 occurred among unvaccinated individuals. Nearly all patients (95.2 %) received oseltamivir, and over 60 % required antibiotics due to bacterial coinfections. The rise in hospitalizations and mortality likely resulted from population vulnerability and post-pandemic effects rather than increased viral severity. Findings emphasize the need for improved vaccination coverage, enhanced surveillance, and timely antiviral access. Reducing antibiotic overuse through better influenza prevention is crucial for combating antibiotic resistance. Continued monitoring through the FluTer registry is essential for optimizing influenza management and preparedness.