Influenza (Flu)



The flu is caused by a virus. There are many different strains of flu virus. The strains often change from year to year. The flu virus may be spread by:

  • An infected person sneezes or coughs and those nearby breathe in droplets that were released
  • 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 past health. A physical exam may be done. Diagnosis is usually based on symptoms.

The doctor may take samples from the nose or throat for testing but it is rare.



Most can clear the virus on their own. Treatment can help to ease symptoms. The flu usually lasts 7 to 10 days. A cough or tiredness may last longer. 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
  • Symptom treatment with over-the-counter medicine, 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.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Edits to original content made by Denver Health.