Risk of Influenza-Like Illness in an Acute Health Care Setting During Community Influenza Epidemics in 2004-2005, 2005-2006, and 2006-2007

Abstract
Nosocomial outbreaks of influenza-like illness (ILI) or influenza are reported regularly.1-3 Patients and health care workers (HCWs) may become infected themselves and, in turn, be sources of infection for others. Attack rates greater than 60% have been found in nursing homes during seasonal epidemics, with 10% lethality from influenza-related complications.4 The incidence rates in short-stay units are less well known. Seasonal influenza remains a frequent cause of hospitalization, and it was observed that the hospitalization rate increased during the influenza A/H1N1 pandemic.5-7 In the United States, the community attack rates of seasonal influenza ranged from 10% to 20% by population groups and the hospitalization rate from 20 to 1000 per 100 000 inhabitants.8 Therefore, the risk of the virus spreading in health care settings is a major concern, especially in the elderly and individuals with immunosuppression or severe chronic disease.