Epidemiological and clinical characteristics of community-acquired and nosocomial influenza cases and risk factors associated with complications: A four season analysis of all adult patients admitted in a tertiary hospital.

Background: Information on the characteristics of patients with nosocomial influenza and associated complications is scarce. This study compared epidemiological and clinical characteristics of patients admitted with hospital-acquired influenza (HAI) to those with community-acquired influenza (CAI) and analyzed risk factors associated with complications.

Methods: This retrospective, observational study included all adult patients with confirmed influenza virus infection admitted to Son Espases University Hospital during the influenza season in Spain (October to May) from 2012-2013 to 2015-2016.