influenza /in′flo̅o̅·en″zə/ [It, influence] , a highly contagious infection of the respiratory tract caused by orthomyxovirus and transmitted by airborne droplet infection. It occurs in isolated cases, epidemics, and pandemics. Symptoms include sore throat, cough, fever, muscular pains, and weakness. The incubation period is brief (from 1 to 3 days), and the onset is usually sudden, with chills, fever, respiratory symptoms, headache, myalgia, and extreme fatigue. Treatment is symptomatic and usually involves bed rest, acetaminophen, and drinking of fluids. Fever and constitutional symptoms distinguish influenza from the common cold. Complete recovery in 3 to 10 days is the rule, but bacterial pneumonia may occur among high-risk patients, such as the elderly, the very young, and people who have chronic pulmonary disease, and lead to death. On average, 5% to 20% of the population suffer influenza infection annually, and approximately 56,000 die. Three main strains of influenza virus have been recognized: type A, type B, and type C. New strains of the virus emerge at regular intervals and are named according to their geographic origin, for example, Asian flu. Yearly vaccination with the currently prevalent strain of influenza virus is recommended for elderly or debilitated persons and health care personnel. Treatment or prophylaxis in high-risk patients may be achieved with rimantadine. Oseltamavir (oral) and Zanamivir (aerosol), when administered within 48 hours of onset, can lessen the severity and duration of symptoms. Also called flu, grippe, la grippe.
