Study on symptoms of adults in hospital at least 24 hours. Confirm the outbreak of influenza 2009 before beginning the campaign vaccination against influenza 2009 detection of infection confirmed influenza infections (H1N1 2009.) by RTPCR in the respiratory system (after sinus or nose and throat and samples from the lower respiratory tract in patients) The study was approved by the Institutional Coordination Service Center Hospital universitari de bellvitge and the consent from the patient. Patients were divided into two groups: groups the hospital admission in the pandemic period and the beginning of pandemic influenza by the season. Epidemiological characteristics and effect of patients with influenza A (H1N1) 2009 pneumonia during these periods were compared.