. Sixty-four percent of these subjects had pneumonia on admission, 26% had respiratory failure, and 11% required care in the ICU. Dyspnea and the presence of infiltrates on chest x-rays were the most common signs among the subjects with H1N1. All subjects were treated with antiviral therapy, and 75% received antibiotic treatment based on their clinical and laboratory findings. The predictive factors of ICU admission were severe hypoxemia and lymphocytosis. CONCLUSIONS: The outcome of subjects with influenza A (H1N1) virus infection was influenced by the severity of the disease on admission, the subjects' underlying conditions, and complications during hospitalization.