Flu Symptoms & Diagnosis

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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.

Is it Flu or COVID-19?

Some of the symptoms of flu and COVID-19 are similar, making it hard to tell the difference between them based on symptoms alone. Diagnostic testing can help determine if you are sick with flu or COVID-19.

Flu Testing
Flu Symptoms & Complications

Flu viruses can cause mild to severe illness. Learn common symptoms and complications.

Diagnosis

A number of tests are available to detect influenza viruses.

The Difference Between Flu and COVID-19

Flu and COVID-19 are both contagious respiratory illnesses, but they are caused by different viruses.

The Difference Between Cold and Flu

Flu and the common cold are both respiratory illnesses but they are caused by different viruses.

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*/feeling feverish or 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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