Influenza, also known as the flu, is a highly contagious infection of the breathing system (nose, throat and lungs) caused by flu viruses.
Seasonal flu is caused by viruses that already circulate among people. Most people have some immunity and a vaccine is available to help prevent the flu. In the United States, flu season usually starts in late fall and lasts throughout the winter, sometimes into early spring. Each year, more than 200,000 people in the U.S. are hospitalized from complications of the flu, and about 36,000 die as a result.
Did You Know?
- An annual flu vaccine is the best way to fight the flu.
- Flu vaccine is safe and effective.
- Flu vaccine cannot cause the flu.
- The Centers for Disease Control and Prevention (CDC) recommend that everyone 6 months and older get vaccinated against the flu EVERY year, especially people who are at high risk.
Pandemic flu refers to an outbreak caused by a new flu virus (such as the 2009 H1N1 flu virus) that spreads around the world. The disease can spread easily from person to person because people have little natural immunity when a new virus is identified. There is no vaccine ready to protect against pandemic flu because the new virus strain must be identified before a vaccine can be produced, which can take up to six months. Pandemic flu is much more serious than seasonal flu and is likely to cause many more deaths.
Learn more about pandemic flu.
How Flu Spreads
The main way flu viruses spread is from person to person when an infected person coughs, sneezes or talks. When someone with the flu coughs or sneezes, droplets containing the virus are sprayed into the air. Someone else can become infected if they breathe the infected droplets, or touch infected droplets on surfaces and then touch their own eyes, nose or mouth.
Symptoms of Flu
Flu symptoms can often be confused with the common cold, but the flu usually comes on more suddenly and is more severe than the common cold. Symptoms of flu may include fever (usually high), headache, tiredness and weakness (can be extreme), dry cough, sore throat, runny or stuffy nose, body or muscle aches, nausea, vomiting and diarrhea (much more common among children than adults). People with colds are more likely to have a runny or stuffy nose and typically do not develop serious health problems.
A person who is sick with the flu is contagious, meaning they can spread the virus. Adults can be contagious from one day before having symptoms to seven days after getting sick. Children can be contagious for even longer than seven days.
Learn more about the difference between flu and a common cold and how to care for yourself at home when you are sick with the flu.
Preventing the Flu
Getting an annual flu vaccine protects yourself, your family, and the vulnerable people in your community. Find a flu vaccine clinic near you.
Learn more ways to fight the flu.
Complications of Flu and When to Seek Care
In some people, flu can cause serious complications such as bacterial pneumonia, dehydration and heart failure. The people most at risk of complications for seasonal flu are:
- Children younger than 2 years.
- Adults 65 and older.
- People with weakened immune systems and chronic illnesses such as asthma, congestive heart failure and diabetes.
If you have underlying medical conditions you are at greater risk of developing flu-related complications; you should consult your doctor if you have flu symptoms.
Other Types of Flu
Flu Information for Health Care Professionals and Laboratories
Physicians and laboratories are encouraged to report any laboratory-confirmed influenza (including rapid tests) to the Fairfax County Health Department. Please contact the Communicable Disease/Epidemiology unit with any questions at 703-246-2433.
Monitoring Flu Activity
The Virginia Department of Health (VDH) and Fairfax County Health Department monitor the level of activity of influenza-like illness (ILI) each week from October through May. Those are the months when flu is most likely to occur in Virginia, and that time period is referred to as the “flu season.”
- Pneumonia and Influenza deaths in Fairfax County.
- Number of students absent from Fairfax County schools.
- Influenza-like illnesses reported from specific medical offices in Fairfax County.
- Influenza-like illness and respiratory illness hospital emergency department and selected pediatric urgent care visits.
- Selected laboratory data.
This information is used to:
- Determine outbreaks.
- Track patterns of illnesses.
- To measure illness impact.
See VDH weekly surveillance reports.
For information about national flu surveillance, go to CDC's Flu Activity & Surveillance web page.
Download these educational materials for your home, work, faith community and elsewhere.
Germ Stopper Poster for Clinic Setting (English/Spanish)