What Are Symptoms of the Flu?

Reviewed on 1/14/2022

A mother feeling her sick daughter's forehead in bed
When you start coming down with the flu (influenza virus), symptoms appear quickly and include fever (not always), chills, cough, sore throat, runny nose, nasal congestion, muscle or body aches, headache, fatigue/tiredness, feeling unwell (malaise), and vomiting and diarrhea (more common in children).

The flu (influenza) is a 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.

Symptoms of the flu (influenza) usually come on suddenly and may include:

The flu can have symptoms similar to COVID-19, however, COVID-19 can cause more severe symptoms and complications.

What Causes the Flu?

The flu (influenza) is caused by influenza viruses transmitted from person-to-person through respiratory droplets propelled 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 without washing their hands first.

  • People with the flu are most contagious in the first three to four days after their illness begins and is generally considered contagious for at least a week after symptoms start.
  • 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.
  • If you have the flu, The Centers for Disease Control (CDC) recommends staying home from work or school for at least 24 hours after fever has gone away on its own, without the use of fever-reducing medications. 

How Is the Flu Diagnosed?

The flu (influenza) is diagnosed based upon the patient’s reported symptoms and a physical examination, along with tests including:

  • Rapid influenza diagnostic tests (RIDTs) 
    • Provides results in about 15 minutes
    • Less accurate than other flu tests called 
  • 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?

The flu (influenza) is treated with home remedies and antiviral medicines in some cases. 

Home remedies to help relieve symptoms of the flu include: 

  • Rest
  • Drinking plenty of fluids
  • Breathing in steam from a bowl of hot water or shower
  • Clean humidifier or cool mist vaporizer
  • Saline nasal spray or drops
  • Suck on lozenges 
    • Do not give lozenges to young children as they can be a choking hazard
  • Over-the-counter (OTC) medicines for relief of symptoms 

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. 


A Cold or The Flu? How to Tell the Difference See Slideshow

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Reviewed on 1/14/2022
Image Source: iStock Images