Influenza viruses spread from human to human via aerosols created when an infected individual coughs or sneezes. Infection occurs after an immunologically susceptible person inhales the aerosol. As in other viral infections, systemic symptoms result from release of inflammatory mediators. The incubation period of influenza ranges from 1 to 4 days. Aerosol transmission may occur 1 day before the onset of symptoms; thus, it may be possible for transmission to occur from asymptomatic persons or persons with subclinical disease who may be unaware that they have been exposed to the disease.
Influenza results from infection with one of three basic types of influenza virus: A, B, or C. Influenza A is generally more pathogenic than influenza B. Epidemics of influenza type C have been reported, especially in young children and military recruits; however, the disease course is usually less severe than that associated with influenza A. Fever is less prominent with type C.
Viral shedding occurs at the onset of symptoms or just before the onset of illness (0-24 hours). Shedding continues for 5-10 days. Young children may shed virus longer, placing others at risk of contracting infection. In highly immunocompromised persons, shedding may persist for weeks to months.
Transmission of influenza from poultry or pigs to humans appears to occur predominantly as a result of direct contact with infected animals. The risk is especially high during slaughter and preparation for consumption; eating properly cooked meat poses no risk.
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Cite this: Michael Stuart Bronze. Fast Five Quiz: Influenza - Medscape - Nov 06, 2018.