OBJECTIVES: To examine trends in hospital length of stay, seasonality and total costs in patients with influenza.

METHODS: The latest available 2015 National Inpatient Sample (NIS) data set of hospital admissions from the Healthcare Cost and Utilization Project was utilized in order to determine the number of hospital admissions for patients with influenza (identified by ICD-9 for Q1-Q3 and ICD-10 codes for Q4). The LOS and costs were compared by payer type, race, season, and age groups.

RESULTS: Based on our inclusion criteria we found 17,158 admissions, representing 0.260% of all hospitalizations. The mean age was 61.17 years (SD: 27.47, Median 70 years). The overall mean LOS was 4.7 days (SD: 5.67, Median 3 days). Majority of the hospitalizations were in patients age 60+ (65%), followed by age 45-60 (12%). Most influenza related hospitalization occurred in winter, with highest in January (45%), followed by February (18%).

Mean (SD) LOS by age: 0-18: 3 days (SD: 7, n= 2161), 18-45: 4.01 days (SD: 6.16, n= 1655), 45-59: 4.76 days (SD: 7.24, n= 2170), 60+: 4.94 days (SD: 4.72, n= 11172). The mean LOS by payer: Medicare: 4.97 days (SD: 4.78), Medicaid: 4.53 days (SD: 8.47), Private: 4.11 days (SD: 5.34).

The overall mean charges were $35,248 (SD: $64799). The mean costs by age group were 0-18: $35175 (SD: $118443), 18-45: $32978 (SD: $58359), 45-59: $38662 (SD: $78999), 60+: $34935 (SD: $44913). The mean costs by payer type were: Medicare: $34859 (SD: $44026), Medicaid: $37976 (SD: $102994), Private: $34584 (SD: $79309).

CONCLUSIONS: Patients with influenza incur some costs for public and private payers due to the need for hospitalization. While costs are moderate, the length of stay poses significant burden on hospitals. Newer more effective treatments are needed to lower the LOS for hospitals.