Influenza (also called the flu) is a viral infection. It affects the respiratory system. It can be mild to severe. In certain people it can be fatal.

There are three types:

  • Type A
  • Type B
  • Type C—the least common

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The flu is caused by a virus. There are different strains of flu virus. The strains often change from year to year.

The flu virus may be spread by:

  • Breathing in droplets—when an infected person sneezes or coughs
  • Touching surfaces contaminated with the virus—then touching the mouth or nose

Risk Factors

Things that raise the risk of getting the flu are:

  • Living or working in crowded areas—such as nursing homes, schools, daycare centers, and the military
  • Being physically or mentally disabled

Some people have a higher risk for severe flu, or problems from the flu. This includes children less than 5 years old and adults over 50 years old. Other things that raise the risk are:

  • Certain health conditions, such as:
    • Asthma
    • Diabetes
    • Diseases of the heart, kidneys, liver, blood, or nervous system
    • A weak immune system
  • Pregnancy
  • Living in long-term care facilities
  • Being American Indian or Alaska Native
  • Obesity


Symptoms usually start quickly. They may be:

  • High fever and chills
  • Headache and severe muscle aches
  • Severe tiredness
  • Lack of hunger, or nausea, vomiting, and diarrhea
  • Cough, sneezing, and runny or stuffy nose
  • Watery eyes, or red eyes from conjunctivitis
  • Sore throat
  • Swollen lumps (lymph nodes) in the neck


The doctor will ask about your symptoms and health history. A physical exam may be done. Diagnosis is usually based on symptoms.

The doctor may take samples from the nose or throat for testing. This can confirm the diagnosis.


The flu usually lasts 7 to 10 days. A cough or tiredness may last longer. The goal is to ease symptoms and prevent problems.

People with severe symptoms or problems may be treated in the hospital.

Treatment options are:

  • Home care—such as rest and drinking plenty of fluids
  • Over-the-counter or prescription medicines, such as:
    • Acetaminophen or ibuprofen—to reduce pain and fever
    • Cough remedies
    • Decongestants—to ease stuffiness
    • Antihistamines— to ease a runny nose, or itchy and watery eyes
    • Antiviral medicines—for severe symptoms or people at risk for them


To reduce the risk of getting the flu:

  • Get a yearly flu vaccine—if the doctor says it is okay
  • Wash hands often
  • Stay away from people who are sick
  • Do not share drinks or personal items
  • Keep surfaces clean with disinfectants

Antiviral medicines may be advised for certain people.


Centers for Disease Control and Prevention
World Health Organization


Public Health Agency of Canada
The College of Family Physicians of Canada


Gaitonde DY, Moore FC, et al. Influenza: diagnosis and treatment. Am Fam Physician. 2019;100(12):751-758.
Inactivated influenza VIS. Centers for Disease Control and Prevention website. Available at: Accessed January 29, 2021.
Influenza. American Lung Association website. Available at:
...(Click grey area to select URL)
Accessed January 29, 2021.
Influenza in adults. EBSCO DynaMed website. Available at: Accessed January 29, 2021.
Influenza in children. EBSCO DynaMed website. Available at: . Accessed January 29, 2021.
Key facts about seasonal influenza (flu). Centers for Disease Control and Prevention website. Available at: Accessed January 29, 2021.
Seasonal influenza vaccination. EBSCO DynaMed website. Available at: Accessed on February 24, 2021.
What you should know about flu antiviral drugs. Centers for Disease Control and Prevention website. Available at: Accessed January 29, 2021.
Last reviewed January 2021 by EBSCO Medical Review Board Mary Beth Seymour, RN
Last Updated: 2/24/2021

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