Clinical Characteristics of Influenza-Associated Pneumonia of Adults: Clinical Features and Factors Contributing to Severity and Mortality

Background: Pneumonia is a major complication of influenza that contributes to mortality. Clinical characteristics and factors of influenza virus contributing to the severity and mortality of pneumonia have not been fully elucidated. Objective: The objective was to clarify clinical characteristics and factors contributing to the severity and mortality of influenza-associated pneumonia (flu-p). Methods: We retrospectively analyzed patients with flu-p. Results: From December 1999 to March 2016, 210 patients with a median age of 69 (range, 17 to 92) years with flu-p based on positive rapid antigen tests, increased antibody titers of paired sera, or positive results of reverse transcription polymerase chain reaction were admitted to our institution. A multivariate analysis found that advanced age (≥ 65 years), pneumonia subtypes (unclassified), diabetes mellitus, and acute kidney injury complicated with flu-p were independent factors associated with disease severity, whereas pneumonia subtypes (mixed viral and bacterial pneumonia and unclassified), healthcare-associated pneumonia, acute kidney injury complicated with flu-p, and severity on admission (severe) were independent factors associated with non-survival. Conclusion: The clinical characteristics of flu-p are varied, and the contribution of several factors to the severity and mortality of flu-p suggest their importance in either preventing flu-p or managing flu-p after it develops.