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.

PLAIN LANGUAGE SUMMARY

This study described the healthcare resource utilization (HCRU) and costs for US adults ≥18 years old hospitalized with influenza and associated secondary complications such as pneumonia, asthma exacerbation and malignant hypertension between 2016–2023. The researchers analyzed a hospital admission database and found that, for the healthcare system, average cost per influenza-related hospitalization ranged from $11,384 to $14,494, depending on the influenza season and age of the patient. Over 96% of patients admitted to a hospital initially presented at the emergency department, 20–30% of patients required mechanical ventilation (MV) or intensive care unit (ICU) admission, and the median hospital length of stay was 3–4 days. This study adds to the existing evidence by providing economic burden estimates for the 2022/23 influenza season, the most recent influenza season after the COVID-19 pandemic, and found slightly lower HCRU and cost for influenza hospitalizations relative to prior seasons. Also, the study comprehensively analyzed economic burden by patient age groups and found lower HCRU and costs among patients ≥65 years compared to adults 18–49 years and 50–64 years consistently for all seasons. Additionally, the study found that the proportion of patients with MV usage alone, with MV usage and an ICU admission, and average hospitalization costs were greatest among patients 50–64 years, highlighting the potential benefit of increasing rates of seasonal influenza vaccination among this age group. Finally, the study found higher costs among patients with complications related to their influenza infection compared to patients without complications. Overall, the study found that influenza-related hospitalization can contribute to substantial economic burden in the US in the most recent time period.

Keywords:

• Influenza
• hospitalization
• health care resources utilization
• cost
• secondary complication

JEL CLASSIFICATION CODES:

• I11
• I1
• I
• I12

Transparency

Declaration of funding

The study was sponsored and funded by Pfizer, Inc., New York, NY.

Declaration of financial/other interests

All authors are current employees of Pfizer, Inc.

Author contributions

All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship for this article. All authors contributed to study conception and design, data acquisition, analysis, and interpretation, drafting and revising of the manuscript, and have given their approval for this manuscript version to be published.

Acknowledgements

We would like to acknowledge Jingying Zhou and Sachin Heerah for their programming support on this project. Grace Lin, an employee of Novosys Health, provided editorial support in the drafting of this manuscript, which was funded by Pfizer, Inc.

Data availability statement

Data generated during this study are available upon request.

Reviewer disclosures

Peer reviewers on this manuscript have received an honorarium from JME for their review work but have no other relevant financial relationships to disclose.

Previous presentations

None.

Notes

i Chronic conditions included dementia, rheumatic disease, peptic ulcer disease, diabetes with and without chronic complications, hemiplegia or paraplegia, any malignancy (solid and hematologic malignancies with the exception of malignant neoplasm of the skin), metastatic solid tumors, moderate or severe liver disease, and acquired immunodeficiency syndrome (AIDS)/human immunodeficiency virus (HIV). Medical conditions that are also considered to be secondary complications of influenza were not evaluated as a chronic condition. 4. Centers for Disease Control and Prevention. People at Higher Risk of Flu Complications: U.S. Department of Health & Human Services; 2023 [updated August 25, 2023; cited 2023 October]. Available from: https://www.cdc.gov/flu/highrisk/index.htm.