Influenza, also known as the flu, is a contagious disease
that is caused by the influenza virus. It attacks the
respiratory tract in humans (nose, throat, and lungs).
The flu is different from a cold. Influenza usually
comes on suddenly and may include these symptoms:
These symptoms are usually referred to as "flu-like
symptoms." Please also see the fact sheet "Is
it a Cold or Flu?" for more information on flu symptoms.
- Tiredness (can be extreme)
- Dry cough
- Sore throat
- Nasal congestion
- Body aches
Anyone Can Get the Flu, But the
Disease Is More Severe for Some People
Most people who get influenza will recover in one to two weeks,
but some people will develop life-threatening complications
(such as pneumonia) as a result of the flu. Millions of people
in the United States — about 10% to 20% of U.S. residents
— will get influenza each year. An average of about
36,000 people per year in the United States die from influenza,
and 114,000 per year have to be admitted to the hospital as
a result of influenza. Anyone can get the flu (even healthy
people), and serious problems from influenza can happen at
any age. People age 65 years and older, people of any age
with chronic medical conditions, and very young children are
more likely to get complications from influenza. Pneumonia,
bronchitis, and sinus and ear infections are three examples
of complications from flu. The flu can make chronic health
problems worse. For example, people with asthma may experience
asthma attacks while they have the flu, and people with chronic
congestive heart failure may have worsening of this condition
that is triggered by the flu.
For a list of groups that are at high risk for complications
from influenza, see: Who Should Get the Flu Vaccine.
The Flu Season
In the Northern hemisphere, winter is the time for flu. In
the United States, the flu season can range from November
through March, and even past March in some years. During the
past 21 flu seasons, months with the heaviest flu activity
(peak months) occurred in December in 4 years, January in
5 years, February in 9 years, and March in 3 years.
Peak Months for Flu Activity
Overthe past 21 years
How the Influenza Virus Is Passed
The flu is spread, or transmitted, when a person who has the
flu coughs, sneezes, or speaks and sends flu virus into the
air, and other people inhale the virus. The virus enters the
nose, throat, or lungs of a person and begins to multiply,
causing symptoms of influenza. Influenza may, less often,
be spread when a person touches a surface that has flu viruses
on it – a door handle, for instance – and then
touches his or her nose or mouth.
The Flu Is Contagious
A person can spread the flu starting one day before he or
she feels sick. Adults can continue to pass the flu virus
to others for another three to seven days after symptoms start.
Children can pass the virus for longer than seven days. Symptoms
start one to four days after the virus enters the body. Some
persons can be infected with the flu virus but have no symptoms.
During this time, those persons can still spread the virus
How To Know if You Have the Flu
Your respiratory illness might be the flu if you have sudden
onset of body aches, fever, and respiratory symptoms, and
your illness occurs during November through April (the usual
flu season in the Northern Hemisphere). However, during this
time, other respiratory illnesses can cause similar symptoms
and flu can be caught at any time of the year. It is impossible
to tell for sure if you have the flu based on symptoms alone.
Doctors can perform tests to see if you have the flu if you
are in the first few days of your illness.
What You Should Do If You Get the Flu
- Drink plenty of liquids
- Avoid using alcohol and tobacco
- Take medication to relieve the symptoms of flu
Influenza is caused by a virus, so antibiotics (like penicillin)
don't work to cure it. The best way to prevent the flu is
to get an influenza vaccine (flu shot) each fall, before flu
Do Not Give Aspirin To a Child
or Teenager Who Has the Flu
Never give aspirin to children or teenagers who have flu-like
symptoms – and particularly fever – without first
speaking to your doctor. Giving aspirin to children and teenagers
who have influenza can cause a rare but serious illness called
Reye syndrome. Children or teenagers with the flu should get
plenty of rest, drink lots of liquids, and take medicines
that contain no aspirin to relieve symptoms.
The Myth of the "Stomach
Many people use the term "stomach flu" to describe
illnesses with nausea, vomiting, or diarrhea. These symptoms
can be caused by many different viruses, bacteria, or even
parasites. While vomiting, diarrhea, and being nauseous or
"sick to your stomach" can sometimes be related
to the flu – particularly in children – these
problems are rarely the main symptoms of influenza. The flu
is a respiratory disease and not a stomach or intestinal disease.
provided by the Centers for Disease Control and Prevention