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Normal lung anatomy
Normal lung anatomy


Nasal spray flu vaccine
Nasal spray flu vaccine



The flu is an infection of the nose, throat, and lungs caused by the influenza virus.

See also: Swine flu (H1N1)

Alternative Names:

Influenza A; Influenza B

Causes, incidence, and risk factors:

Influenza A usually arrives between early winter and early spring. Influenza B can appear at any time of the year. H1N1, or swine flu, is another type of influenza.

Most people catch the flu when they breathe in tiny droplets from coughs or sneezes of someone who has the flu. It is also spread when you touch a surface, such as a faucet handle or phone that has the virus on it, and then touch your mouth, nose, or eyes.

Symptoms appear 1 - 7 days later (usually within 2 - 3 days). The flu spreads easily. It often strikes a community all at once. Many students or workers become sick within 2 or 3 weeks of the flu's arrival in a school or workplace.

Sometimes people confuse colds and flu. They do share some of the same symptoms. But most people get a cold several times each year and the flu only once every few years.

People call a viral illness that makes them throw up or have diarrhea "stomach flu." This is incorrect. The flu virus does not cause the stomach symptoms. Flu infections mostly cause symptoms in the nose, throat, and lungs.


The flu usually begins quickly. The first symptoms are a fever between 102 and 106 °F. (An adult typically has a lower fever than a child.)

Other common symptoms include:

  • Body aches
  • Chills
  • Dizziness
  • Flushed face
  • Headache
  • Lack of energy
  • Nausea and vomiting

Between day 2 and day 4 of the illness, the fever and "whole body" symptoms begin to fade. Then breathing symptoms begin to increase.

  • The symptom is usually a dry cough .
  • Most people also develop a sore throat and headache.
  • Runny nose (a clear, watery nasal discharge) and sneezing are common.

These symptoms (except the cough) usually go away in 4 - 7 days. Sometimes, the fever returns. The cough and feeling tired may last for weeks.

Other symptoms may include:

  • Loss of appetite
  • Asthma, chronic obstructive pulmonary disease (COPD), heart failure or other long-term illness may become worse

Signs and tests:

Most people of 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 case.

People who become very sick with the flu, or who are at high risk for flu complications, may want to see a health care provider.

The provider will do a thorough physical exam. Only rarely is, a ray, blood work, or sputum cultures needed.

When flu is widespread in the community, a doctor can make a diagnosis after hearing the symptoms. No further testing is needed.

There is a test to detect the flu. It is done by swabbing the nose and throat. The results of this test can be available rapidly. At times, this test can help your health care provider decide the best treatment.



Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) help lower fever. Sometimes doctors suggest you use both types of medicine.

  • Take acetaminophen every 4 - 6 hours.
  • Take ibuprofen every 6 - 8 hours.
  • Do NOT use aspirin.

A fever does not need to come all the way down to normal. Most people will feel better when their temperature drops by even 1 degree.

Over-the-counter cold medicines may make some of your symptoms better. Cough drops will help with your sore throat.

Take these steps also:

  • Rest
  • Drink plenty of liquids
  • Avoid alcohol and tobacco


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 become very sick with the flu
  • Who are at high risk for flu complications

These drugs 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.

The medicines that may be used are zanamivir (Relenza) or oseltamivir (Tamiflu).

Children at risk of a severe case of the flu may also need these medicines.

Support Groups:

Expectations (prognosis):

Millions of people in the United States get the flu each year. Most get better within a week or two.

But thousands become sick. They need to stay in the hospital. About 36,000 people die each year from complications of the flu.

Anyone at any age can have serious complications from the flu, but those at highest risk include:

  • People over age 50
  • Children between 6 months and 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

In most people who are healthy, the flu goes away within 7 - 10 days.


Possible complications, especially for those at high risk, include:

Calling your health care provider:

Call your health care provider if:

  • Your are in a high-risk category and develop symptoms of the flu
  • Your illness seems very bad


Steps to take in order to avoid catching or spreading 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.
  • Cover your cough with a tissue and throw away after use.
  • Carry hand sanitizer with you. Use it often during the day and always after touching your face.
  • Cough into your sleeve if a tissue is not available.
  • Avoid touching your eyes, nose, and mouth.

A yearly vaccine is recommended for children older than 6 months, adolescents, and adults.

  • The vaccine used in the 2010 - 2011 flu season will also protect against swine (H1N1) flu.
  • The vaccine is available as a flu shot or a nasal spray-type flu vaccine.

For specific recommendations, see influenza vaccine .


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.

Seasonal flu: what to do if you get sick . Centers for Disease Control and Prevention. Accessed October 4, 2010.

Review Date: 10/5/2010
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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