Influenza (Flu)


General Information · Symptoms · Prevention

General Information

Influenza (flu) is a contagious respiratory illness caused by influenza viruses. It can cause mild to severe illness. Serious outcomes of flu infection can result in hospitalization or death. Some people, such as older people, young children, and people with certain health conditions, are at high risk of serious flu complications.

Most experts believe that flu viruses spread mainly by tiny droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby. Less often, a person might also get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.

You may be able to pass on the flu to someone else before you know you are sick, as well as while you are sick. Although people with the flu are most contagious in the first 3-4 days after their illness begins, some otherwise healthy adults may be able to infect others beginning 1 day before symptoms develop and up to 5 to 7 days after becoming sick. Some people, especially young children and people with weakened immune systems, might be able to infect others with flu viruses for an even longer time.

The time from when a person is exposed to flu virus and infected to when symptoms begin is about 1 to 4 days, with an average of about 2 days.


People who have the flu often feel some or all of these signs and symptoms that usually start suddenly, not gradually:

  • Fever*Not everyone with flu will have a fever or feeling feverish/chills
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Muscle or body aches
  • Headaches
  • Fatigue (very tired)
  • Some people may have vomiting and diarrhea, though this is more common in young children than in adults.

* It’s important to note that not everyone with flu will have a fever.


The CDCCenters for Disease Control and Prevention recommends three steps to prevent influenza from spreading:

  • Take time to get a yearly flu vaccine
  • Take everyday preventative actions to stop the spread of germs
    • Avoid close contact with sick people
    • Wash your hands often with soap and water
    • Avoid touching your eyes, nose, and mouth
  • Take flu antiviral drugs if your doctor prescribes them