What is influenza (flu)?
The flu is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. The best way to prevent the flu is by getting a flu vaccination each year.
It is estimated that every year in the United States, on average:
- 5% to 20% of the population gets the flu;
- more than 200,000 people are hospitalized from flu complications;
- 20,000 of those hospitalized are children younger than 5 years of age; and
- a range of 3,000 to 49,000 people die from flu.
Some people, such as older people, young children, and people with certain health conditions (such as asthma, diabetes, or heart disease), are at high risk for serious flu complications.
How does the flu spread?
Most experts believe that flu viruses spread mainly by droplets made when people with the flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might also get the flu by touching a surface or object that has the flu virus on it and then touching their own mouth, eyes or possibly their nose.
What are the symptoms of the flu?
Symptoms of the flu include:
- fever (usually high)
- headache
- extreme tiredness
- dry cough
- sore throat
- runny or stuffy nose
- muscle aches
- Stomach symptoms, such as nausea, vomiting, and diarrhea, also can occur but are more common in children than adults
Although the term “stomach flu” is sometimes used to describe vomiting, nausea, or diarrhea, these illnesses are caused by certain other viruses, bacteria, or possibly parasites, and are rarely related to influenza. Also see Cold Versus Flu.
How long is a person with flu virus contagious?
The period when an infected person is contagious depends on the age and health of the person. You may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Most healthy adults may be able to infect others beginning 1 day before symptoms develop and 5 to 7 days after becoming sick. Some people, especially young children and people with weakened immune systems, might be able to infect others for an even longer time.
What is the difference between a cold and the flu?
The flu and the common cold are both respiratory illnesses but they are caused by different viruses. Because these two types of illnesses have similar symptoms, it can be difficult to tell the difference between them based on symptoms alone. In general, the flu is worse than the common cold, and symptoms such as fever, body aches, extreme tiredness, and dry cough are more common and intense. Colds are usually milder than the flu. People with colds are more likely to have a runny or stuffy nose. Colds generally do not result in serious health problems, such as pneumonia, bacterial infections, or hospitalizations.
How can you tell the difference between a cold and the flu?
Because colds and flu share many symptoms, it can be difficult (or even impossible) to tell the difference between them based on symptoms alone. Special tests that usually must be done within the first few days of illness can be carried out, when needed to tell if a person has the flu.
Preventing and Treating the Flu
What can I do to protect myself against the flu?
CDC recommends a yearly flu vaccine as the first and most important step in protecting against this serious disease. While there are many different flu viruses, the flu vaccine protects against the main flu viruses that research indicates will cause the most illness during the flu season. (Three or four viruses, depending on which vaccine you get.) The vaccine can protect you from getting sick from these viruses or it can make your illness milder if you get a different flu virus. See Vaccine Benefits for more information.
If you do get the flu, antiviral drugs are an important treatment option. Antiviral drugs are prescription medicines (pills, liquid or an inhaler) that fight against the flu by keeping flu viruses from reproducing in your body. Antiviral drugs can make your illness milder and make you feel better faster. They may also prevent serious flu complications. This could be especially important for people at high risk. For treatment, antiviral drugs work best if started soon after getting sick (within 2 days of symptoms). Visit Treatment - Antiviral Drugs for more information.
In addition, you should take everyday preventive actions to stop the spread of germs, like flu. This includes staying away from sick people, frequent hand washing, and cleaning and disinfecting frequently touched surfaces, especially if someone is ill, to decrease your chances of getting or spreading the flu. If you are sick with flu, reduce your contact with others and cover your cough to help keep germs from spreading. See Preventing the Flu: Good Health Habits Can Help Stop Germs for more information.