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Flu Symptoms & Severity

What are the signs and symptoms of the flu?

Flu vs Cold

Signs and Symptoms Influenza Cold
Symptom onset Abrupt Gradual
Fever Usual; lasts 3-4 days Rare
Aches Usual; often severe Slight
Chills Fairly common Uncommon
Fatigue, weakness Usual Sometimes
Sneezing Sometimes Common
Stuffy nose Sometimes Common
Sore throat Sometimes Common
Chest discomfort, cough Common; can be severe Mild to moderate; hacking cough
Headache Common Rare

Flu Symptoms

Influenza (also known as the flu) is a contagious respiratory illness caused by flu viruses. It can cause mild to severe illness, and at times can lead to death. The flu is different from a cold. The flu usually comes on suddenly. People who have the 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.

Flu Complications

Most people who get influenza will recover in a few days to less than two weeks, but some people will develop complications (such as pneumonia) as a result of the flu, some of which can be life-threatening and result in death.

Pneumonia, bronchitis, sinus and ear infections are examples of complications from flu. The flu can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic congestive heart failure may experience worsening of this condition that is triggered by the flu.

People at High Risk from Flu

Anyone can get the flu (even healthy people), and serious problems related to the flu can happen at any age, but some people are at high risk of developing serious flu-related complications if they get sick. This includes people 65 years and older, people of any age with certain chronic medical conditions (such as asthma, diabetes, or heart disease), pregnant women, and young children.

What are the emergency warning signs of flu sickness?

In children

  • Fast breathing or trouble breathing
  • Bluish skin color
  • Not drinking enough fluids
  • Not waking up or not interacting
  • Being so irritable that the child does not want to be held
  • Flu-like symptoms improve but then return with fever and worse cough
  • Fever with a rash

In adults

  • Difficulty breathing or shortness of breath
  • Pain or pressure in the chest or abdomen
  • Sudden dizziness
  • Confusion
  • Severe or persistent vomiting
  • Flu-like symptoms that improve but then return with fever and worse cough

In addition to the signs above, get medical help right away for any infant who has any of these signs:

  • Being unable to eat
  • Has trouble breathing
  • Has no tears when crying
  • Significantly fewer wet diapers than normal

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