Influenza or flu is a viral infection of the nose, throat, bronchial tubes and lungs. Influenza occurs most often in the winter months. Illnesses resembling influenza may occur in the summer months but they are usually due to other viruses. Influenza is highly contagious and is easily transmitted through contact with droplets from the nose and throat of an infected person during coughing and sneezing. Typical flu symptoms include headache, fever, chills, cough and body aches.
Intestinal symptoms are uncommon.
Although most people are ill for only a few days, some people have a much more serious illness, such as pneumonia and may need to be hospitalized. Thousands of people die each year in the United States from the flu or related complications. The incubation period for influenza is one to five days. Usually, a doctor will diagnose a case of the flu based on typical symptoms of fever, chills, headache, cough and body aches. Specific lab tests to confirm the flu are costly and time consuming and are usually limited to outbreak or disease surveillance efforts.