Influenza-associated pneumonia among hospitalized patients with 2009 pandemic influenza A (H1N1) virus--United States, 2009.

BACKGROUND: Pneumonia was a common complication among hospitalized patients with 2009 pandemic influenza A H1N1 [pH1N1] in the United States in 2009.

METHODS: Through 2 national case series conducted during spring and fall of 2009, medical records were reviewed. A pneumonia case was defined as a hospitalized person with laboratory-confirmed pH1N1 virus and a chest radiographic report consistent with pneumonia based on agreement among 3 physicians.

RESULTS: Of 451 patients with chest radiographs performed, 195 (43%) had pneumonia (spring, 106 of 237 [45%]; fall, 89 of 214 [42%]). Compared with 256 patients without pneumonia, these 195 patients with pneumonia were more likely to be admitted to the intensive care unit (52% vs 16%), have acute respiratory distress syndrome (ARDS; 26% vs 2%), have sepsis (18% vs 3%), and die (17% vs 2%; P < .0001). One hundred eighteen (61%) of the patients with pneumonia had ≥1 underlying condition. Bacterial infections were reported in 13 patients with pneumonia and 2 patients without pneumonia. Patients with pneumonia, when compared with patients without pneumonia, were equally likely to receive influenza antiviral agents (78% vs 79%) but less likely to receive antiviral agents within ≤2 days of illness onset (28% vs 50%; P < .0001).

CONCLUSIONS: Hospitalized patients with pH1N1 and pneumonia were at risk for severe outcomes including ARDS, sepsis, and death; antiviral treatment was often delayed. In the absence of accurate pneumonia diagnostics, patients hospitalized with suspected influenza and lung infiltrates on chest radiography should receive early and aggressive treatment with antibiotics and influenza antiviral agents.