(flu) The flu, also called influenza, is a respiratory infection caused by viruses. Each year, millions of Americans get sick with the flu. Sometimes it causes mild illness. But it can also be serious or even deadly, especially for people over 65, newborn babies, and people with certain chronic illnesses. The flu is caused by flu viruses that spread from person to person. When someone with the flu coughs, sneezes, or talks, they spray tiny droplets. These droplets can land in the mouths or noses of people who are nearby. Less often, a person may get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes. Symptoms of the flu come on suddenly and may include: Fever or feeling feverish/chills; Cough; Sore throat; Runny or stuffy nose; Muscle or body aches; Headaches; Fatigue (tiredness). Some people may also have vomiting and diarrhea. This is more common in children. Sometimes people have trouble figuring out whether they have a cold or the flu. There are differences between them:

Signs and Symptoms	Cold	Flu
Start of symptoms	Slowly	Suddenly
Fever	Rarely	Usually
Aches	Sometimes (slight)	Usually
Fatigue, weakness	Sometimes	Usually
Headache	Rarely	Common
Stuffy nose, sneezing, or sore throat	Common	Sometimes

Sometimes people say that they have a "flu" when they really have something else. For example, "stomach flu" isn't the flu; it's gastroenteritis. Some people who get the flu will develop complications. Some of these complications can be serious or even life-threatening. They include: Bronchitis; Ear infection; Sinus infection; Pneumonia; Inflammation of the heart (myocarditis), brain (encephalitis), or muscle tissues (myositis, rhabdomyolysis). The flu also can make chronic health problems worse. For example, people with asthma may have asthma attacks while they have flu. Certain people are more likely to have complications from the flu, including: Adults 65 and older; Pregnant women; Children younger than 5; People with certain chronic health conditions, such as asthma, diabetes, and heart disease. To diagnose the flu, health care providers will first do a medical history and ask about your symptoms. There are several tests for the flu. For the tests, your provider will swipe the inside of your nose or the back of your throat with a swab. Then the swab will be tested for the flu virus. Some tests are quick and give results in 15-20 minutes. But these tests are not as accurate as other flu tests. These other tests can give you the results in one hour or several hours. Most people with the flu recover on their own without medical care. People with mild cases of the flu should stay home and avoid contact with others, except to get medical care. But if you have symptoms of flu and are in a high risk group or are very sick or worried about your illness, contact your health care provider. You might need antiviral medicines to treat your flu. Antiviral medicines can make the illness milder and shorten the time you are sick. They also can prevent serious flu complications....

Acute viral infection involving the respiratory tract; marked by inflammation of the nasal mucosa, the pharynx, and conjunctiva, and by headache and severe, often generalized, myalgia.

An acute viral infection of the respiratory tract, occurring in isolated cases, in epidemics, or in pandemics; it is caused by serologically different strains of viruses (influenzaviruses) designated A, B, and C, has a 3-day incubation period, and usually lasts for 3 to 10 days. It is marked by inflammation of the nasal mucosa, pharynx, and conjunctiva; headache; myalgia; often fever, chills, and prostration; and occasionally involvement of the myocardium or central nervous system.

(influenza, human) An acute viral infection in humans involving the respiratory tract. It is marked by inflammation of the NASAL MUCOSA; the PHARYNX; and conjunctiva, and by headache and severe, often generalized, myalgia.

Influenza is a viral respiratory infection causing fever, coryza, cough, headache, and malaise. Mortality is possible during seasonal epidemics, particularly among high-risk patients (eg, those who are institutionalized, at the extremes of age, have cardiopulmonary insufficiency, or are in late pregnancy); during pandemics, even healthy,...

Influenza, one of the most common infectious diseases, is a highly contagious airborne disease that occurs in seasonal epidemics and manifests as an acute febrile illness with variable degrees of systemic symptoms, ranging from mild fatigue to respiratory failure and death. Influenza causes significant loss of workdays, human suffering,...

Influenza is a viral infection that attacks your respiratory system - your nose, throat and lungs. Influenza is commonly called the flu, but it's not the same as stomach "flu" viruses that cause diarrhea and vomiting.

Influenza, an acute viral infection of the upper or lower respiratory tract that is marked by fever, chills, and a generalized feeling of weakness and pain in the muscles, together with varying degrees of soreness in the head and abdomen. Influenza is caused by any of several closely related...