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 airborne droplets from the 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 a year. On the contrary, 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 to 7 days after you come in contact with the virus. Most of the time symptoms appear within 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 co-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 often has a lower fever than a child.
Millions of people in the United States get the flu each year. Most people get better within a week or two, but thousands of people with the flu develop pneumonia or a brain infection. They need to stay in the hospital. About 36,000 people in the U.S. die each year of problems from the flu.
Anyone at any age can have serious complications from the flu. Those at highest risk include:
People over the age of 65
Children younger than 2 years old
Women who are more than 3 months pregnant
Anyone living in a long-term care facility
Anyone with chronic heart, lung, or kidney conditions, diabetes, or a weakened immune system
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 your fever has 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 mouth with a tissue when coughing 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.
Centers for Disease Control and Prevention. What you should know for the 2014-2015 influenza season. August 14, 2014.
Centers for Disease Control and Prevention. What you should know about flu antiviral drugs. September 17, 2013.
Centers for Disease Control and Prevention. Seasonal influenza: flu basics. July 28, 2014.
Grohskopf LA, Olsen SJ, Sokolow LZ, 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, 2014-2015. MMWR Weekly. 2014;63(32):691-697.
Jefferson T, Jones M, Doshi P, et al. Neuraminidase inhibitors for preventing and treating influenza in healthy adults and children. Cochrane Database Syst Rev. 2014(4):CD008965. DOI: 10.1002/14651858.CD008965.pub4.
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, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.