Background: Influenza is an infectious disease that can lead to complications requiring hospitalization and may even result in death, particularly in patients at extreme ages. Our objective is to analyze hospitalized patients with an ICD-10 diagnostic code for influenza (codes J09, J10, and J11) in any diagnostic position from 2016 to 2021 in the Spanish hospital surveillance system.
Methods: Information on age, admissions, length of hospital stay, lethality, mortality, and comorbidity with a diagnostic code for influenza between October 1, 2016, and September 30, 2021, was obtained from the National Hospital Data Surveillance System (Conjunto Mínimo Básico de Datos, CMBD).
Results: A total of 118,585 hospital admissions with an influenza diagnose were recorded. Out of these, 57,671 patients (48.63%) were males, while 60,914 (51.37%) were females. The overall median age of admissions was 70.5 years. Significant differences were found among different age groups, with those over 65 years being the largest group in this study. The hospitalization rate for the entire period was 42.13 cases per 100,000 inhabitants. The overall mortality rate for the observed period was 2.45 deaths per 100,000 inhabitants, being higher in the group over 85 years. The most common comorbidity in the studied patients was diabetes mellitus, followed by chronic obstructive pulmonary disease and congestive heart failure. The latter group showed higher lethality than those patients with any other comorbidity. The average length of hospital stay was 9.59 days.
Conclusions: Influenza is an important cause of hospitalization in Spain. Male gender, older age groups, and associated clinical risk conditions showed a direct relationship with hospital mortality. This suggests that influenza vaccination should be implemented in the population to reduce associated comorbidities, as well as the mortality resulting from them.