Please cite this paper as: Bramley et al. Intensive care unit patients with 2009 pandemic influenza A (H1N1pdm09) virus infection – United States, 2009. Influenza and Other Respiratory Viruses 6(601), e134–e142.
Background The influenza A (H1N1pdm09) [pH1N1] virus resulted in intensive care unit (ICU) admissions, acute respiratory distress syndrome (ARDS), and death.
Objectives To describe the characteristics of ICU patients with pH1N1 virus infection in the United States during the spring and fall of 2009 and to describe the factors associated with severe complications including ARDS and death.
Patients/Methods Through two national case-series conducted during spring and fall of 2009, medical charts were reviewed on ICU patients with laboratory-confirmed pH1N1 infection by real-time reverse-transcriptase polymerase chain reaction.
Results The majority (77%) of 154 patients hospitalized in an ICU were <50 years of age, and 65% had at least one underlying medical condition. One hundred and twenty-eight (83%) patients received influenza antiviral agents; 29% received treatment ≤2 days after illness onset. Forty-eight (38%) patients developed ARDS and 37 (24%) died. Patients with ARDS were more likely to be morbidly obese (36% versus 19%, P = 0·04) and patients who died were less likely to have asthma (11% versus 28%, P = 0.05). Compared with patients who received treatment ≥6 days after illness onset, patients treated ≤2 days after illness onset were less likely to develop ARDS (17% versus 37%, P < 0.01) or die (7% versus 35%, P < 0·01).
Conclusions Among patients hospitalized in an ICU with pH1N1 virus infection, ARDS was a common complication, and one-quarter of patients died. Patients with asthma had less severe outcomes. Early treatment with influenza antiviral agents was likely beneficial, especially when initiated ≤2 days after illness onset.