The flu is an infection of the nose, throat, and lungs. It spreads easily.
This article discusses influenza types A and B. Another type of the flu is the swine flu (H1N1).
Influenza A; Influenza B
The flu is caused by an influenza virus.
Most people get the flu when they breathe in tiny droplets from coughs or sneezes of someone who has the flu. You can also catch the flu if you touch something with the virus on it, and then touch your mouth, nose, or eyes.
People often confuse colds and flu. They are different. But, you might have some of the same symptoms. Most people get a cold several times each year. Most people get the flu only once every few years.
Sometimes, you can get a virus that makes you throw up or have diarrhea. Some people call this the "stomach flu." This is a misleading name because this virus is not the actual flu. The flu mostly affects your nose, throat, and lungs.
Flu symptoms will often start quickly. You can start to feel sick about 1-7 days after you come in contact with the virus. Most of the time symptoms appear in 2-3 days.
The flu spreads easily. It can affect a large group of people in a very short amount of time. For example, students and workers get sick within 2 or 3 weeks of the flu's arrival in a school or workplace.
The first symptom is a fever between 102 and 106 °F. An adult usually has a lower fever than a child.
Call your health care provider if you get the flu and think you are at risk for having complications.
Also call your health care provider if your flu symptoms are very bad and self-treatment is not working.
You can take steps to avoid catching or spreading the flu. The best step is to get a flu vaccine.
If you have the flu:
Stay in your apartment, dorm room, or home for at least 24 hours after any fever is gone.
Wear a mask if you leave your room.
Avoid sharing food, utensils, cups, or bottles.
Use hand sanitizer often during the day and always after touching your face.
Cover your cough with a tissue and throw it away after use.
Cough into your sleeve if a tissue is not available. Avoid touching your eyes, nose, and mouth.
The Centers for Disease Control and Prevention (CDC) recommends that everyone 6 months and older should receive the influenza vaccine.
Grohskopf LA, Shay DK, Shimabukuro TT, et al; Centers for Disease Control and Prevention (CDC). Prevention and control of seasonal influenza with vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP) – United States, 2013-2014. MMWR Recomm Rep. 2013 Sep 20; 62(RRO7);1-43.
Jefferson T, Jones M, Doshi P, Del Mar C. Neuraminidase inhibitors for preventing and treating influenza in healthy adults: systematic review and meta-analysis. BMJ. 2009 Dec 8; 339:b5106.
Centers for Disease Control and Prevention. What you should know for the 2013-2014 influenza season. January 8, 2014.
Centers for Disease Control and Prevention. Seasonal influenza: flu basics. September 12, 2013.
Centers for Disease Control and Prevention.What you should know about flu antiviral drugs. September 17, 2013.
Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.