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
Causes, incidence, and risk factors
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.
Sometimes people 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. Usually, a person gets the flu 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." But, that is misleading. It is not a flu. The flu mostly affects your nose, throat, and lungs.
Flu symptoms usually start quickly. You can start to feel sick about 1 - 7 days after you are around the virus. Usually, symptoms start 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.
The fever and aches and pains begin to go away on days 2-4. But new symptoms occur, including:
Increased breathing symptoms
Runny nose (clear and watery)
Most symptoms usually go away in 4 - 7 days. But the cough and feeling tired may last for weeks. Sometimes, the fever comes back.
Some people may not feel like eating.
The flu can make asthma, breathing problems, and other long-term illnesses worse.
Signs and tests
Most people do not need to see a doctor or nurse when they have flu symptoms. This is because most people are not at risk for a severe flu.
If you are very sick with the flu, you may want to see your doctor or nurse. People who are at high risk for flu complications may also want to see a doctor if they get the flu.
When many people in an area have flu, a doctor can make a diagnosis after hearing about your symptoms. No further testing is needed.
There is a test to detect the flu. It is done by swabbing the nose or throat. Most of the time, test results are available very fast. The test can help your health care provider decide the best treatment.
HOW DO I TREAT MY SYMPTOMS?
Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) help lower fever. Sometimes doctors suggest you use both types of medicine. Do NOT use aspirin.
A fever does not need to come all the way down to normal. Most people feel better when the temperature drops by 1 degree.
Over-the-counter cold medicines may make some of your symptoms better. Cough drops or throat sprays will help with your sore throat.
You will need a lot of rest. Drink plenty of liquids. Do not smoke or drink alcohol.
WHAT ABOUT ANTIVIRAL DRUGS?
Most people with milder symptoms feel better in 3 - 4 days. They do not need to see a doctor or take antiviral medications.
Doctors may give antiviral drugs to people who get very sick with the flu. You may need these medicines if you are more likely to have flu complications.
These medicines may shorten the time you have symptoms by about 1 day. They work better if you start taking them within 2 days of your first symptoms.
Children at risk of a severe case of the flu may also need these medicines.
Millions of people in the United States get the flu each year. Most 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 age 65
Children younger than 2 years
Women more than 3 months pregnant during the flu season
Anyone living in a long-term care facility
Anyone with chronic heart, lung, or kidney conditions, diabetes, or a weakened immune system
Call your doctor or nurse if you get the flu and think you are at risk for having complications.
Also call your doctor or nurse 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 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.
Fiore AE, Fry A, Shay D, et al; Centers for Disease Control and Prevention (CDC). Antiviral agents for the treatment and chemoprophylaxis of influenza --- recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2011 Jan 21;60(1):1-24.
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.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, and Stephanie Slon.