Influenza - Symptoms

The first symptoms of infection appear one to four days after the virus has entered a person's body. They include headache, dry cough, and chills. These symptoms are followed quickly by overall achiness and a fever that may run as high as 104°F (40°C). As the fever declines, nasal (nose) congestion and a sore throat become noticeable. The flu leaves an individual very tired and weak. A person with the flu may not return to normal for several days or even a few weeks.

A flu infection often leads to more serious complications. These complications are often caused by bacteria that get into the lower respiratory tract. The signs of a secondary (follow-up) infection often appear just as the person seems to be recovering from the flu. These signs include a high fever, chills, chest pains, and a cough that produces a thick, yellowish sputum (discharge from the throat). If these symptoms appear, medical treatment should be sought.

A magnified image of an influenza virus budding on the surface of an infected cell. (Reproduced by permission of

CNRI/Science Photo Library, National Audubon Society Collection/Photo Researchers, Inc.

)

Secondary infections also affect the sinus or ears. The flu can also worsen heart and lung problems and certain other chronic diseases. For this reason, an attack of the flu can be especially serious for elderly people.