Pneumonia among adults hospitalized with laboratory-confirmed seasonal influenza virus infection-United States, 2005-2008

Background: Influenza and pneumonia combined are the leading causes of death due to infectious diseases in the United States. We describe factors associated with pneumonia among adults hospitalized with influenza. Methods: Through the Emerging Infections Program, we identified adults >= 18 years, who were hospitalized with laboratory-confirmed influenza during October 2005 through April 2008, and had a chest radiograph (CXR) performed. Pneumonia was defined as the presence of a CXR infiltrate and either an ICD-9-CM code or discharge summary diagnosis of pneumonia. Results: Among 4,765 adults hospitalized with influenza, 1392 (29 %) had pneumonia. In multivariable analysis, factors associated with pneumonia included: age >= 75 years, adjusted odds ratio (AOR) 1.27 (95 % confidence interval 1.10-1.46), white race AOR 1.24 (1.03-1.49), nursing home residence AOR 1.37 (1.14-1.66), chronic lung disease AOR 1.37 (1.18-1.59), immunosuppression AOR 1.45 (1.19-1.78), and asthma AOR 0.76 (0.62-0.92). Patients with pneumonia were significantly more likely to require intensive care unit (ICU) admission (27 % vs. 10 %), mechanical ventilation (18 % vs. 5 %), and to die (9 % vs. 2 %). Conclusions: Pneumonia was present in nearly one-third of adults hospitalized with influenza and was associated with ICU admission and death. Among patients hospitalized with influenza, older patients and those with certain underlying conditions are more likely to have pneumonia. Pneumonia is common among adults hospitalized with influenza and should be evaluated and treated promptly.