Flu Symptoms & Diagnosis

sick woman in bed man checking temperature on thermometer

Influenza (also known as “flu”) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness, and at times can lead to death. This page provides resources about flu symptoms, complications, and diagnosis.

Common Flu Signs & Symptoms

Flu signs and symptoms usually come on suddenly. People who are sick with flu often feel some or all of these symptoms:

  • Fever* or feeling feverish/chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headaches
  • Fatigue (tiredness)
  • Some people may have vomiting and diarrhea, though this is more common in children than adults.

*It’s important to note that not everyone with flu will have a fever.

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