Hospitalized patients with 2009 H1N1 influenza infection: the Mayo Clinic experience

To describe the clinical course and outcome of adults hospitalized with the 2009 H1N1 influenza infection.

In this retrospective study, we reviewed the electronic medical records of patients with H1N1 influenza infection treated at Mayo Clinic in Rochester, MN, from May 1, 2009, through December 31, 2009.

We identified 1053 patients with H1N1 influenza infection; this study consists of 66 hospitalized adults (6%). Patients' mean +/- SD age was 46.9+/-17.8 years. The 3 most common comorbidities were hypertension in 31 patients (47%), obesity in 29 (44%), and diabetes mellitus in 21 (32%). The most common symptoms were cough in 58 patients (88%), fever or chills in 55 (83%), and dyspnea in 47 (71%). Twenty-nine patients (44%) were admitted to the intensive care unit (ICU). Dyspnea and thrombocytopenia were more common in the ICU patients. The hospital, 28-day, and 90-day mortality rates were 8% (5/66), 11% (7/66), and 14% (9/66), respectively. Among the 29 ICU patients, 23 (79%) received mechanical ventilation, and 16 (55%) developed acute lung injury or acute respiratory distress syndrome. Rescue therapy for refractory respiratory failure was provided for 6 patients (21%). Of the 29 ICU patients, 10 (34%) required vasopressor support, and 4 (14%) required acute renal replacement therapy.

Hospitalized adults with H1N1 influenza infection are relatively young, and a significant number require treatment in the ICU. Among the patients who require ICU admission, most develop acute lung injury or acute respiratory distress syndrome and require mechanical ventilator support.