Presentation (CTI)

OBJECTIVES: Characterizing the burden of influenza is essential to inform public health strategies. This study presents age-stratified data on the clinical and economic inpatient burden of influenza and influenza-like illness (ILI) across three seasons (2022-2023 to 2024-2025) in individuals aged ≥18 years in Germany, with emphasis on those aged ≥50 years.
METHODS: Inpatient episodes with an ICD-10-GM diagnosis of J09-J11 as the primary cause of hospitalization were extracted from a nationwide hospital database (InEK). An influenza season was defined as a 12-month period from July to June of the following year. Outcomes by age group (18-49, 50-54, 55-59, 60-64, 65-74, 75-79, ≥80 years) included: hospitalizations, incidence per 100,000, mean length of stay (LOS), proportions treated in intensive care units (ICU), in-hospital mortality, and mean hospitalization costs.
RESULTS: Influenza/ILI hospitalizations totaled 33,306, 40,907, and 62,510 in 2022-2023, 2023-2024, and 2024-2025, respectively. Hospitalization incidence and in-hospital mortality increased substantially with age across all seasons (e.g., 2024-2025: 29.8-385.3 per 100,000 and 0.8%-10.9%, respectively, from 18-49 to ≥80). Mean LOS varied between 3.9 and 8.3 days across age groups and seasons. In each season, proportions treated in ICU were lowest in age groups 18-49 and ≥80 with 7.8%-9.8%. ICU proportions were comparable between age groups 50-59 and 60-79, with values ranging from 13.5% to 15.6% across groups and seasons. Mean costs per age group and season ranged between €2,662 and €6,321 and peaked between 55 and 74 years.
CONCLUSIONS: Older adults have the highest hospitalization incidence and in-hospital mortality. However, hospitalized adults aged 50-59 years already show an average resource utilization, measured through ICU treatment and costs per case, that exceeds that of younger adults and is similar to or higher than that of older age groups.