Determinants of hospitalization and pneumonia in influenza during the post-pandemic era: Role of influenza A+B coinfection.

OBJECTIVE

In influenza, the impact of evolving diagnostic and therapeutic approaches in the post-pandemic-period on the clinical course has not yet been fully clarified. This-study evaluated the determinants of hospitalization, pneumonia-development, and clinical-outcomes in patients with polymerase chain reaction (PCR) confirmed influenza.

METHODS

In this retrospective, single-center study, patients aged ≥18 years with PCR-confirmed influenza A, B, or A + B coinfection between January 2023 and December 2025 were included. Demographic-clinical, and laboratory data were analyzed. Factors associated with hospitalization and pneumonia were identified using multivariable logistic regression analysis.

RESULTS

A total of 371 patients were included in the study, of whom 34.2% required hospitalization. Influenza A was the most common type (59.3%), while influenza A + B coinfection was observed in 21.6% of PCR-confirmed cases. Pneumonia developed in 28.3% of patients and was associated with worse clinical outcomes In multivariable analysis, advanced age (OR: 1.03; p = 0.002), hypertension (OR: 3.45; p < 0.001), and influenza A + B coinfection (OR: 3.92; p < 0.001) were associated with the development of pneumonia. Hypertension (OR: 3.90; p = 0.002), COPD (OR: 3.65; p < 0.001), congestive heart failure (OR: 8.33; p = 0.015), and influenza A + B coinfection (OR: 3.74; p < 0.001) were associated with hospitalization. Despite low bacterial growth rates, antibiotic use was high (56.1%; 88.1% among hospitalized patients). Among hospitalized patients, 12.6% required intensive care, 6.3% required mechanical ventilation, and the mortality rate was 4.7%. Pneumonia and comorbidities were present in all fatal cases.

CONCLUSION

Influenza A + B coinfection was associated with hospitalization and pneumonia; however, its impact on mortality could not be reliably assessed due to the limited number of fatal cases. Pneumonia and cardiopulmonary comorbidities were associated with clinical outcomes. The high use of antibiotics and corticosteroids despite limited microbiological evidence highlights a discrepancy between clinical practice and guideline recommendations, underscoring the need for improved antimicrobial stewardship strategies. These findings should be interpreted with caution given the observational design of the study.