Flu is a respiratory infection caused by a number of viruses. The viruses pass through the air and enter your body through your nose or mouth. Between 5% and 20% of people in the U.S. get the flu each year. The flu can be serious or even deadly for elderly people, newborn babies, and people with certain chronic illnesses.
Symptoms of the flu come on suddenly and are worse than those of the common cold. They may include
- Body or muscle aches
- Sore throat
Is it a cold or the flu? Colds rarely cause a fever or headaches. Flu almost never causes an upset stomach. And “stomach flu” isn’t really flu at all, but gastroenteritis.
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. If you get the flu, your health care provider may prescribe medicine to help your body fight the infection and lessen symptoms.
The main way to keep from getting the flu is to get a yearly flu vaccine. Good hygiene, including hand washing, can also help.
Most people who get influenza will recover in several days to less than two weeks, but some people will develop complications as a result of the flu. A wide range of complications can be caused by influenza virus infection of the upper respiratory tract (nasal passages, throat) and lower respiratory tract (lungs). While anyone can get sick with flu and become severely ill, some people are more likely to experience severe flu illness. Young children, adults aged 65 years and older, pregnant women, and people with certain chronic medical conditions are among those groups of people who are at high risk of serious flu complications, possibly requiring hospitalization and sometimes resulting in death. For example, people with chronic lung disease are at higher risk of developing severe pneumonia.
Sinus and ear infections are examples of moderate complications from flu, while pneumonia is a serious flu complication that can result from either influenza virus infection alone or from co-infection of flu virus and bacteria. Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle (myositis, rhabdomyolysis) tissues, and multi-organ failure (for example, respiratory and kidney failure). Flu virus infection of the respiratory tract can trigger an extreme inflammatory response in the body and can lead to sepsis, the body’s life-threatening response to infection. Flu also can make chronic medical problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic heart disease may experience a worsening of this condition triggered by flu.