What is the flu?

The flu is a viral infection that affects the upper respiratory tract, including your nose, throat and lungs. The flu is like a common cold, but symptoms are much worse.

The flu typically does not cause vomiting or diarrhea, though this is a common misconception.

Influenza affects more than three million people in the United States each year and can be especially dangerous to infants and the elderly.

Common Cold (Upper Respiratory Infection) Sinusitis

Causes of the flu

The flu is caused by influenza virus A and B. Many strains of the influenza virus exist and are constantly evolving, making it difficult to prevent getting them.

All of these viruses are contagious and can spread through the air, direct contact and surface contact.

The virus is contagious up to 24 hours before symptoms, so you could pass on the flu to others before you even know you have it.

Risk factors for the flu

People more likely to catch the flu include:

  • Young children
  • Adults over 50 years old
  • People with weakened immune systems 
  • Women who are pregnant
  • Healthcare workers

The biggest risk factor contributing to the flu is not receiving an annual flu shot. The most common influenza strains are used to develop a different flu vaccine each year, which helps prepare your immune system with antibodies to fight off those viruses.

Proper hygiene and handwashing also help prevent the spread of flu.

Symptoms of the flu

Symptoms of flu are worse than the common cold and include: 

  • Headache and body aches
  • Fever
  • Nasal congestion
  • Sore or dry throat
  • Cough
  • Chills and sweats
  • Decreased appetite
  • Decreased energy

Diagnosis of the flu

The flu is diagnosed in a physical exam with your primary care provider, typically with an assessment of your symptoms. Sometimes, a clinical test may be administered to confirm diagnosis, which is more common if you are pregnant or have a weakened immune system and for research purposes during seasonal outbreaks.

Influenza tests include:

  • Rapid influenza diagnostic test (RIDT) — detects if any viral antigens are present in nose or throat
  • Rapid molecular assay — similar to RIDT, this test more specifically looks for influenza viruses
  • Viral culture — sometimes taken in addition to rapid tests, this sample is grown in laboratory over 1-2 days and can be used to identify and study specific strains of influenza virus

Treatments for flu

Since the flu is a viral infection, antibiotics cannot be used for treatment. If caught early, your primary care provider may prescribe antiviral drugs to help your immune system fight the infection. The antiviral medication will not cure the flu but can lessen the duration of your infection.

Symptoms of the flu can be treated with:

  • Pain reliever such as acetaminophen or ibuprofen
  • Warm, hydrating fluids
  • Rest — extra sleep helps your immune system fight the infection

People at high risk may need to go to the hospital for treatment. The flu vaccine can help prevent the flu and is recommended for everyone over six months old, especially if you are at high risk for complications from flu symptoms.

Recovery from the flu

Most people recover from the flu within 3-10 days, but you can still be contagious even after symptoms are gone.

You should stay home 24 hours after a fever subsides in order to prevent spreading the flu.

Find a primary care doctor nearby

Mercy Health locations that can treat you