Influenza disease profile

BOX B-1
Influenza

Infectious Agent: Orthomyxoviruses, RNA viruses that infect birds and mammals. Three genera cause influenza: Influenza A, which is the most common cause of disease and has varying serotypes; Influenza B, which has only one serotype; and Influenza C, the least common.

Routes of Transmission: Airborne aerosols and direct contact with secretions or contaminated surfaces.

Health Effects: Influenza illness typically begins with chills or fever. The illness often involves cough, sore throat, nasal congestion, muscle aches, headache, and fatigue. It typically lasts for several days. In contrast with common colds, influenza usually has high fever with sudden onset and extreme fatigue. Influenza can also cause pneumonia either directly or through secondary bacterial infection.

Incidence, Prevalence, and Mortality: Influenza causes annual seasonal epidemics throughout the world as well as periodic pandemics. In the United States influenza has been estimated to cause an average of approximately 36,000 annual deaths during 1990–1999 and 226,000 annual hospitalizations during 1979–2001.



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