What Is the Flu?
The flu (influenza) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness that can result in hospitalization or death.
There are two main types of flu (influenza) virus: types A and B that are responsible for seasonal flu epidemics each year.
Most people who get the flu get better within a few days to less than two weeks.
What Are Symptoms of the Flu?
Symptoms of flu (influenza) usually come on suddenly and may include:
- Fever (not everyone with the flu has a fever)
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Vomiting and diarrhea (more common in children)
Some of the symptoms of flu and COVID-19 are similar, making it hard to tell the difference between them based on symptoms alone. Symptoms of the influenza (the flu) and COVID-19 that are similar include:
- Fever or chills
- Muscle or body aches
- Sore throat
- Runny nose
- Stuffy nose/congestion
Diagnostic testing can help determine if you are sick with the flu or COVID-19.
What Causes the Flu?
The flu (influenza) is a contagious respiratory illness caused by influenza viruses transmitted from person-to-person through respiratory droplets thrust into the air when an infected person coughs or sneezes.
Less commonly, the flu is transmitted when a person touches a surface or object that has the virus on it, and then touches their mouth, nose, or eyes.
People with the flu are most contagious in the first three to four days after their illness begins. Symptoms of the flu usually start within 1 to 4 days after exposure to the virus, and you may be contagious before you even feel sick.
How Is the Flu Diagnosed?
Influenza (the flu) is usually diagnosed with:
- Rapid influenza diagnostic tests (RIDTs)
- Provides results in about 15 minutes
- Less accurate than other flu tests
- Rapid molecular assays
- Detects genetic material of the virus and provide results in about 15-20 minutes
- Other specialized flu tests may be used in hospitals or state public health laboratories
- Specialized tests use a long swab to swipe the inside of the nose or the back of the throat, which is sent to a lab for testing
- Results may take several hours
What Is the Treatment for the Flu?
Antiviral medications may be used to treat the flu (influenza) and they work best when taken within 48 hours of the onset of flu symptoms to help reduce the severity and duration of the illness.
Antiviral flu medicines include:
- Oseltamivir phosphate (Tamiflu)
- Zanamivir (Relenza)
- Peramivir (Rapivab)
- Baloxavir marboxil (Xofluza)
Many people who have the flu do not require medical treatment. Home remedies to relieve flu symptoms include:
What Are Complications of the Flu?
Complications of the flu (influenza) include:
- Pneumonia, which can be life-threatening
- Sinus and ear infections
- Inflammation of the heart (myocarditis)
- Inflammation of the brain (encephalitis)
- Inflammation of the muscle (myositis, rhabdomyolysis) tissues
- Multi-organ failure (such as respiratory and kidney failure)
- Extreme inflammatory response that can lead to sepsis, a life-threatening response to infection
- Worsening of chronic medical problems such as asthma or chronic heart disease
How Do You Prevent the Flu?
The Centers for Disease Control (CDC) recommends getting an annual flu vaccine as the best way to prevent the flu (influenza).
Flu vaccines will not prevent COVID-19, but they can reduce the burden of flu illnesses, hospitalizations, and deaths on the health care system and conserve medical resources to care for COVID-19 patients.
Please get immunized. Search pharmacies and clinics in your area; free flu vaccines are offered all over the US.
To protect yourself from getting the flu:
- Wash hands frequently with soap and water for at least 20 seconds.
- If soap and water are not available, use hand sanitizer with at least 60% alcohol and use a sufficient amount to rub in for 20 seconds.
- Do not touch your mouth, nose, or eyes with unwashed hands.
- Avoid close contact with anyone who has been diagnosed with the flu.
- If there is an outbreak in your community, stay at home and limit close contact with others.
To prevent transmission of viral illness:
- For the flu, the CDC recommends that people stay home for at least 24 hours after their fever is gone (without use of a fever-reducing medication) except to get medical care or other necessities.
- Wear a face mask around other people if you are sick.
- Cover your mouth and nose with a tissue or the inside of your elbow when you cough or sneeze. Discard used tissues. Immediately wash hands with soap and water for at least 20 seconds or use a hand sanitizer with at least 60% alcohol if soap and water is not available.
- Clean and disinfect frequently touched surfaces daily. This includes countertops, doorknobs, handles, tables, light switches, phones, keyboards, toilets, faucets, and sinks. Use EPA-registered household disinfectants.
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