You may feel fine one hour and have a high fever the next. These acute symptoms usually last 3 to 5 days. They often start improving gradually after the first 48 hours or so. Infection with the flu virus often leads to other infections. Ear, sinus, and bronchial infections are examples of such infections.
Pneumonia can also occur as a result of the flu.
It can be caused by the influenza virus itself or by bacteria invading the virus-damaged lung tissues. An unusual complication of flu is Reye's syndrome, which usually occurs in children and adolescents and rarely occurs in adults. A link has been shown between the use of aspirin during influenza illness and the development of Reye's syndrome. Influenza can usually be diagnosed from your symptoms. Your health care provider may do a physical exam to rule out other types of infection, such as strep throat and sinusitis.