"Seasonal influenza, a respiratory infection caused by the influenza virus is a significant cause of morbidity and mortality, especially in individuals who are at the extremes of age, pregnant, immune compromised, or have chronic underlying disease. Morbidity and hospitalization rates for influenza among healthy children less than 2 years of age are similar to those among adults over 65 years of age.
As with most acute viral respiratory infections, seasonal influenza occurs annually in the winter months, and healthcare-associated outbreaks may follow or parallel outbreaks in the community, which usually last from 6 to 8 weeks. Outbreaks are often characterized by abrupt onset and rapid transmission. Most reported outbreaks of influenza have occurred in long-term care facilities. However, outbreaks have also been reported on pediatric, medical, and geriatric wards, and in adult and neonatal intensive care units.
The most important reservoirs of the influenza virus are infected persons. Infection may be introduced into a healthcare facility by patients, personnel or visitors. The period of communicability is generally 3-7 days from clinical onset. Prolonged shedding may occur in immune compromised individuals. Transmission is by large droplet spread and by contact. The influenza virus can survive for several hours on environmental surfaces
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