Economic burden and secondary complications of influenza-related hospitalization among adults in the US: a retrospective cohort study

Abstract

Objective This study aims to describe the healthcare resource utilization (HCRU) and direct medical cost of influenza-related hospitalizations to illustrate the persistent economic burden of influenza among adults in the US. Methods A retrospective cohort study was conducted using the PINC AI Healthcare Database. Adults hospitalized with a diagnosis of influenza between August 1–May 31 from 2016–2023 were identified and stratified by age (18–49, 50–64 and ≥65 years). The index hospitalization was defined as the individual’s first influenza-related hospitalization during each season. Patient demographics, comorbidities, and hospitalization characteristics were assessed during the index hospitalization. Index hospitalization length of stay (LOS), in-hospital mortality, intensive care unit (ICU) admissions, mechanical ventilation (MV) usage, and costs were evaluated overall and by MV usage, ICU admission, and secondary complication status. Pre-index influenza-related outpatient and emergency department (ED) visits (7 days prior) were also evaluated. Results Primarily initiated in the ED, the median LOS for influenza-related hospitalizations was 3–4 days. Inpatient mortality increased with age (2.2–4.4%). Combined mean hospitalization and initial ED visit costs were $12,556–$14,494 (2017/18; high severity season) and $11,384–$12,896 (2022/23; most recent season). Compared to other age groups, adults ≥65 years had higher proportions of hospitalization with no MV or ICU usage. Adults 18–49 years had the highest proportion of ICU admission only, whereas adults 50–64 years had the highest MV usage only and both MV and ICU admission. MV and/or ICU usage was associated with higher hospitalization costs. Increasing proportionally with age, the majority of influenza-related hospitalizations had a secondary complication diagnosis, which were associated with elevated costs. Limitations Analysis of this hospital-based administrative database relied on coding accuracy. Only hospital system-associated outpatient/ED visits were captured; the full scope of HCRU was under-ascertained. Conclusions The economic burden of influenza-related hospitalizations remains substantial, driven by underlying conditions, MV/ICU usage and secondary complications.