Flu
Influenza A; Influenza B; Oseltamivir (Tamiflu) - flu; Zanamivir (Relenza) - flu; Vaccine - fluThe flu is an infection of the nose, throat, and lungs. It spreads easily from person to person.
This article discusses influenza types A and B. A type of influenza A infection due to the H1N1 influenza strain is commonly called the swine flu.
Swine flu.
The H1N1 virus (swine flu) is an infection of the nose, throat, and lungs. It is caused by the H1N1 influenza virus.
Causes
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. In contrast, people generally 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 usually not the actual flu. The flu mostly affects your nose, throat, and lungs.
Stomach flu
Viral gastroenteritis is present when a virus causes an infection of the stomach and intestine. The infection can lead to diarrhea and vomiting. It...
Symptoms
Flu symptoms 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 to 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 often 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°F (39°C) and 106°F (41°C). An adult often has a lower fever than a child.
Fever
Fever is the temporary increase in the body's temperature in response to a disease or illness. A child has a fever when the temperature is at or abov...
Other common symptoms include:
- Body aches
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Chills
Chills
Chills refers to feeling cold after being in a cold environment. The word can also refer to an episode of shivering along with paleness and feeling ...
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Dizziness
Dizziness
Dizziness is a term that is often used to describe 2 different symptoms: lightheadedness and vertigo. Lightheadedness is a feeling that you might fai...
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Headache
Headache
A headache is pain or discomfort in the head, scalp, or neck. Serious causes of headaches are rare. Most people with headaches can feel much better...
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Nausea and vomiting
Nausea and vomiting
Nausea is feeling an urge to vomit. It is often called "being sick to your stomach. "Vomiting or throwing-up forces the contents of the stomach up t...
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The fever, aches, and pains begin to go away on days 2 through 4. But new symptoms may occur, including:
- Dry cough
- Increased symptoms that affect breathing
- Runny nose (clear and watery)
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Sneezing
Sneezing
A sneeze is a sudden, forceful, uncontrolled burst of air through the nose and mouth.
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Sore throat
Sore throat
Pharyngitis, or sore throat, is discomfort, pain, or scratchiness in the throat. It often makes it painful to swallow.
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Most symptoms go away in 4 to 7 days. The cough and tired feeling 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 (chronic) illnesses and conditions worse.
Exams and Tests
Most people do not need to see a health care provider when they have flu symptoms. This is because most people are not at risk for a severe case of the flu.
If you are very sick with the flu, you may want to see your provider. People who are at high risk for flu complications may also want to see a provider if they get the flu.
When many people in an area have flu, a provider 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 provider determine the best treatment.
Provider determine the best treatment
Many different germs, called viruses, cause colds. Symptoms of the common cold include:CoughHeadacheNasal congestionRunny noseSneezingSore throat Th...
Treatment
HOME CARE
Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) help lower fever. Providers sometimes suggest that you use both types of medicine. Do not use aspirin.
A fever does not need to come all the way down to a normal temperature to make a difference in how a person feels. Most people feel better when the temperature drops by 1 degree Fahrenheit.
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.
ANTIVIRAL DRUGS
Most people with milder symptoms feel better in 3 to 4 days. They do not need to see a provider or take antiviral medicines.
Providers may give antiviral medicines to people who get very sick with the flu. You may need these medicines if you are more likely to have flu complications The health problems below may increase your risk of getting sicker with the flu:
- Lung disease (including asthma)
Asthma
Asthma is a chronic disease that causes the airways of the lungs to swell and narrow. It leads to breathing difficulty such as wheezing, shortness o...
ImageRead Article Now Book Mark Article - Heart conditions (except high blood pressure)
- Kidney, liver, nerve, and muscle conditions
- Blood disorders (including sickle cell disease)
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Diabetes
Diabetes
Diabetes is a long-term (chronic) disease in which the body cannot regulate the amount of sugar in the blood.
ImageRead Article Now Book Mark Article - A weakened immune system due to diseases (such as AIDS), radiation therapy, or certain medicines, including chemotherapy and corticosteroids
AIDS
Human immunodeficiency virus (HIV) is the virus that causes acquired immunodeficiency syndrome (AIDS). When a person becomes infected with HIV, the ...
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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 for a severe case of the flu may also need these medicines.
Children at risk for a severe case of t...
Many different germs, called viruses, cause colds. Symptoms of the common cold include:Runny noseNasal congestionSneezingSore throatCoughHeadache Th...
Outlook (Prognosis)
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 may need to stay in the hospital. About 36,000 people in the United States 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 age 65 or over
- 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
Possible Complications
Complications may include:
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Pneumonia
Pneumonia
Pneumonia is a breathing (respiratory) condition in which there is an infection of the lung. This article covers community-acquired pneumonia (CAP). ...
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Encephalitis (infection of the brain)
Encephalitis
Encephalitis is irritation and swelling (inflammation) of the brain, most often due to infections.
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Meningitis
Meningitis
Meningitis is an infection of the membranes covering the brain and spinal cord. This covering is called the meninges.
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Seizures
Seizures
A seizure is the physical changes in behavior that occurs during an episode of abnormal electrical activity in the brain. The term "seizure" is often...
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When to Contact a Medical Professional
Contact your provider if you get the flu and think you are at risk for having complications.
Also contact your provider if your flu symptoms are very bad and self-treatment is not working.
Prevention
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 (and you are not taking medicine to reduce your fever).
- 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. Children 6 months through 8 years of age may need 2 doses during a single flu season. Everyone else needs only 1 dose each flu season. For the 2022-2023 season, the CDC recommends use of any type of flu shot for those under age 65 and one of 3 high dose vaccines for those age 65 or older. The nasal spray flu vaccine (live attenuated influenza vaccine, or LAIV) may be given to healthy, non-pregnant people 2 through 49 years of age.
References
Aoki FY. Antiviral drugs for influenza and other respiratory virus infections. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 45.
Centers for Disease Control and Prevention website. Influenza: seasonal flu vaccines. www.cdc.gov/flu/prevent/flushot.htm. Updated August 25, 2022. Accessed August 7, 2023.
Centers for Disease Control and Prevention website. Influenza: what you should know about flu antiviral drugs. www.cdc.gov/flu/treatment/whatyoushould.htm. Updated December 15, 2022. Accessed August 7, 2023.
Havers FP, Campbell AJP. Influenza viruses. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 285.
Ison MG, Lee N. Influenza. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 332.
Treanor JJ. Influenza viruses, including avian influenza and swine influenza. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 165.
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Tips on buying cold and flu medicines
Animation
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The difference between a cold and the flu
Animation
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Flu
Animation
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Normal lung anatomy - illustration
Within the respiratory system, air is first inhaled through the nose or mouth into the pharynx. From the pharynx, air is drawn through the larynx and trachea to make its way to the lungs.
Normal lung anatomy
illustration
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Influenza - illustration
Influenza is a viral infection of the respiratory tract that causes coughing, breathing difficulty, fever, headache, muscle aches and weakness. The virus is spread from person to person by inhaling infected droplets from the air.
Influenza
illustration
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Nasal spray flu vaccine - illustration
The flu vaccine can also be administered as a nasal spray instead of the usual injection method. It can be an alternative for healthy, non-pregnant people age 2 to 49 who want to be protected from the flu virus. Unlike the regular vaccine, it is a live virus. Therefore, it is best if the person receiving it does not have close contact with people who have a weakened immune system.
Nasal spray flu vaccine
illustration
-
Tips on buying cold and flu medicines
Animation
-
The difference between a cold and the flu
Animation
-
Flu
Animation
-
Normal lung anatomy - illustration
Within the respiratory system, air is first inhaled through the nose or mouth into the pharynx. From the pharynx, air is drawn through the larynx and trachea to make its way to the lungs.
Normal lung anatomy
illustration
-
Influenza - illustration
Influenza is a viral infection of the respiratory tract that causes coughing, breathing difficulty, fever, headache, muscle aches and weakness. The virus is spread from person to person by inhaling infected droplets from the air.
Influenza
illustration
-
Nasal spray flu vaccine - illustration
The flu vaccine can also be administered as a nasal spray instead of the usual injection method. It can be an alternative for healthy, non-pregnant people age 2 to 49 who want to be protected from the flu virus. Unlike the regular vaccine, it is a live virus. Therefore, it is best if the person receiving it does not have close contact with people who have a weakened immune system.
Nasal spray flu vaccine
illustration
Review Date: 8/15/2022
Reviewed By: Linda J. Vorvick, MD, Clinical Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Internal review and update on 07/12/2023 by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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