About
- 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
Symptoms
Flu can cause mild to severe illness, and at times can lead to death. Flu symptoms usually come on suddenly. People who have flu often feel some or all of these signs and 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 flu will recover in a few days to less than two weeks, but some people will develop complications (such as pneumonia) as a result of flu, some of which can be life-threatening and result in death.
Sinus and ear infections are examples of moderate complications from flu, while pneumonia is a serious flu complication that can result from either flu virus infection alone or from co-infection of flu virus and bacteria. Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle tissues (myositis, rhabdomyolysis), and multi-organ failure (for example, respiratory and kidney failure). Flu virus infection of the respiratory tract can trigger an extreme inflammatory response in the body and can lead to sepsis, the body’s life-threatening response to infection. Flu also can make chronic medical problems worse. For example, people with asthma may experience asthma attacks while they have flu, and people with chronic heart disease may experience a worsening of this condition triggered by flu.
People at Higher Risk from Flu
Anyone can get sick with flu, even healthy people, and serious problems related to flu can happen to anyone at any age, but some people are at higher 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 children younger than 5 years, but especially those younger than 2 years old.
Cold versus Flu
| Signs and Symptoms | Cold | Influenza (Flu) |
| Symptom onset | Gradual | Abrupt |
| Fever | rare | Common; lasts 3-4 days |
| Aches | Slight | Common; often severe |
| Chills | Uncommon | Fairly common |
| Fatigue, weakness | Sometimes | Usual |
Emergency Warning Signs of Flu Complications
| In children Fast breathing or trouble breathing Bluish lips or face Ribs pulling in with each breath Chest pain Severe muscle pain (child refuses to walk) Dehydration (no urine for 8 hours, dry mouth, no tears when crying) Not alert or interacting when awake Seizures Fever above 104 degrees Fahrenheit that is not controlled by fever-reducing medicine In children younger than 12 weeks, any fever Fever or cough that improves but then returns or worsens | In children Fast breathing or trouble breathing Bluish lips or face Ribs pulling in with each breath Chest pain Severe muscle pain (child refuses to walk) Dehydration (no urine for 8 hours, dry mouth, no tears when crying) Not alert or interacting when awake Seizures Fever above 104 degrees Fahrenheit that is not controlled by fever-reducing medicine In children younger than 12 weeks, any fever Fever or cough that improves but then return or worsen |
Diagnosis for Flu
- Flu is a contagious respiratory illness that can cause fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and/or fatigue.
- There are multiple tests that can detect flu viruses.
- Although testing is the only way to know if you have flu, your doctor may diagnose you based on your symptoms.
Symptoms to look out for
Your respiratory illness might be influenza (flu) if you have fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills and/or fatigue. Some people may have vomiting and diarrhea, though this is more common in children. People may be sick with flu and have respiratory symptoms without a fever. Flu viruses usually cause the most illness during the colder months of the year. However, flu can also occur outside of the typical flu season. In addition, other viruses can also cause respiratory illness similar to flu. So, it is impossible to tell for sure if you have flu based on symptoms alone. If your doctor needs to know for sure whether you are sick with flu, there are laboratory tests that can be done.