Influenza is a respiratory infection of the nose, throat, bronchial tubes and lungs. There are two main types of virus: influenza A and influenza B. Each type includes many different strains, which tend to change each year. Seasonal influenza sometimes causes severe illness or complications, but the great majority of people recover fully without any medical treatment.
Influenza is most common during the fall and winter months. Influenza activity often increases during the late fall and early winter in the United States, but peak levels generally occur between late December and early March. Illnesses resembling influenza may occur during the summer months but they are usually due to other viruses.
Anyone can get influenza, but it is most serious in people 65 years and older, young children, and people with chronic underlying health conditions such as asthma, diabetes or a weakened immune system.
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 symptoms include fever, chills, aches, cough and sore throat. Intestinal symptoms, such as vomiting or diarrhea, are possible but uncommon. Although most people are ill for only a few days, influenza sometimes leads to more serious illness, such as pneumonia. in 2014, over 2000 New Yorkers died from influenza and its complications (including pneumonia).
Influenza generally occurs within 1 to 4 days after exposure.
Doctors diagnose influenza by checking for common symptoms such as fever, chills, aches, cough and sore throat. Lab tests are sometimes used to confirm the diagnosis, but these tests are not necessary or useful in most instances.
Most people recover from flu on their own, without medical treatment. They do not need to go to the hospital, but they do need to take steps to avoid spreading the infection. If you have a fever (100 degrees or higher), plus a cough or sore throat, be sure to take these steps:
Some people are more likely than others to get very sick with influenza. People who have flu-like symptoms or have had recent close contact with someone with flu-like symptoms should call a health care provider if they belong to any of these higher risk groups: