It can even cause death, usually among the elderly or those with chronic diseases. Types A and B are usually responsible for the most severe and widespread outbreaks. The flu virus is highly contagious, and is transmitted easily and swiftly from person to person by coughing or sneezing. During the height of their illness, an infected person's respiratory tract secretions are loaded with the virus. When he or she sneezes or coughs, an unsuspecting victim inhales infected droplets from the air.
Symptoms appear after an incubation period of one to three days.
The victim is contagious during incubation and for another three to four days after symptoms appear. How the Flu is Diagnosed Physicians rarely use blood tests or throat cultures to determine if a patient has the flu. Instead, they evaluate the flu status in the community, what the person's symptoms are, and how those symptoms match the characteristics of this year's flu epidemic. Feel Flu symptoms appear within several days of infection. With no complications, the most severe symptoms usually subside after two or three days, although fever may last for five days.