IntroductionInfluenza, or the flu, is a respiratory infection
caused by a variety of flu viruses. The most familiar aspect of the
flu is the way it can "knock you off your feet" as it sweeps through
The flu differs in several ways from the
common cold, a respiratory infection also caused by viruses. For
example, people with colds rarely get fevers or headaches or suffer
from the extreme exhaustion that flu viruses cause.
Centers for Disease Control and Prevention (CDC) estimates that 35
to 50 million Americans come down with the flu during each flu
season, which typically lasts from November to March. Children are
two to three times more likely than adults to get sick with the flu,
and children frequently spread the virus to others. Although most
people recover from the illness, CDC estimates that in the United
States more than 100,000 people are hospitalized and more than
20,000 people die from the flu and its complications every year.
When and Where Do People Usually Get the Flu?Flu outbreaks
usually begin suddenly and occur mainly in the late fall and winter.
The disease spreads through communities creating an epidemic. During
the epidemic, the number of cases peaks in about three weeks and
subsides after another three or four weeks. Half of the population
of a community may be affected. Because schools are an excellent
place for flu viruses to attack and spread, families with school-age
children have more infections than other families, with an average
of one-third of the family members infected each year.
Is the Flu an Important Disease?Besides the rapid start of
the outbreaks and the large numbers of people affected, the flu is
an important disease because it can cause serious complications.
Most people who get the flu get better within a week (although they
may have a lingering cough and tire easily for a while longer). For
elderly people, newborn babies, and people with certain chronic
illnesses, however, the flu and its complications can be
How is the Flu Transmitted?You can get the flu if someone
around you who has the flu coughs or sneezes. You can get the flu
simply by touching a surface like a telephone or door knob that has
been contaminated by a touch from someone who has the flu. The
viruses can pass through the air and can enter your body through
your nose or mouth. If you've touched a contaminated surface, they
can pass from your hand to your nose or mouth.
You are at
greatest risk of getting infected in highly populated areas, such as
in crowded living conditions and in schools.
What are Flu Symptoms?If you get infected by the flu virus,
you will usually feel symptoms one to four days later. You can
spread the flu to others before your symptoms start and for another
three to four days after your symptoms appear. The symptoms start
very quickly and are
Typically, the fever begins to decline on
the second or third day of the illness. The flu almost never causes
symptoms in the stomach and intestines. The illness that some people
often call "stomach flu" is not influenza.
- Dry cough
- Body aches
- Stuffy nose
- Sore throat
How Does a Doctor Diagnose the Flu?Usually, doctors or
other health care workers diagnose the flu on the basis of whether
flu is epidemic in the community and whether the patient's
complaints fit the current pattern of symptoms. Doctors rarely use
laboratory tests to identify the virus during an epidemic. Health
officials, however, monitor certain U.S. health clinics and do
laboratory tests to determine which type of flu virus is responsible
for the epidemic.
How Can I Keep from Getting the Flu?Flu Vaccine
The main way to
keep from getting the flu is to get a yearly flu vaccine. You can
get the vaccine at your doctor's office or a local clinic, and in
many communities at workplaces, supermarkets, and drugstores. You
must get the vaccine every year because it changes.
Scientists make a different vaccine every year because the
strains of flu viruses change from year to year. Nine to 10 months
before the flu season begins, they prepare a new vaccine made from
inactivated (killed) flu viruses. Because the viruses are killed,
they cannot cause infections. The vaccine preparation is based on
the strains of the flu viruses that are in circulation at the time.
It includes those A and B viruses (see section below on types of flu
viruses) expected to circulate the following winter.
Sometimes, an unpredicted new strain may appear after the
vaccine has been made and distributed to doctors and clinics.
Because of this, even if you do get the flu vaccine, you still may
get infected. If you do get infected, however, the disease usually
is milder because the vaccine still will give you some
Your immune system takes time to respond to the
flu vaccine. Therefore, you should get vaccinated six to eight weeks
before flu season begins to prevent getting infected or reduce the
severity of flu if you do get it. The vaccine itself cannot cause
the flu, but you could become exposed to the virus by someone else
and get infected soon after you are
possible side effects from the flu
You should be aware that the
flu vaccine can cause side effects. The most common side effect in
children and adults is soreness at the site of the vaccination.
Other side effects, especially in children who previously have not
been exposed to the flu virus, include fever, tiredness, and sore
muscles. These side effects may begin 6 to 12 hours after
vaccination and may last for up to two days.
producing the vaccine are grown in chicken eggs and then killed with
a chemical so that they can no longer cause an infection. The flu
vaccine may contain some egg protein, which can cause an allergic
reaction. Therefore, if you are allergic to eggs or have ever had a
serious allergic reaction to the flu vaccine, CDC recommends that
you consult with your doctor before getting vaccinated.
Who should get the flu
If you are in any of the
following groups or live in a household with someone who is, CDC
recommends that you get the flu vaccine.
The vaccine can be administered to children as
young as six months old. Children should get the flu vaccine if they
are taking long-term aspirin treatment as they may be at risk of
developing Reye's syndrome following a flu infection (see section on
complications in children). They should also get the flu vaccine if
they live in a household with someone in the above
- You are 50 years of age or older.
- You have chronic diseases of your heart, lungs, or kidneys.
- You have diabetes.
- Your immune system does not function properly.
- You have a severe form of anemia.
- You will be more than three months pregnant during the flu
- You live in a nursing home or other chronic-care housing
Health care workers and volunteers should get the flu
vaccine if they work with patients in any of the above
Although the flu vaccine is the
best way to prevent getting the flu, three antiviral medicines also
are available by prescription that will help prevent flu infection:
The Food and Drug
Administration (FDA) has approved Tamiflu® for use in adults and
adolescents 13 years and older. Rimantadine and amantadine have been
approved for use by adults and children who are 1 year of age and
- Tamiflu® (oseltamivir)
- Flumadine® (rimantadine)
- Symmetrel® (amantadine)
Rimantadine and amantadine have unpleasant side
effects. Your doctor can help you decide which medicine is best for
You should discuss the flu vaccine and the
medicines with your doctor before the flu season begins.
- These medicines help prevent the flu if you take them for at
least two weeks during the outbreak of flu in your community.
- You may use these medicines if you are in close contact with
family members or others who have the flu.
- You may use them if you are in close contact with people who
have been vaccinated but whom you want to give added protection
from getting the flu.
- You may use either medicine immediately following flu
vaccination during a flu epidemic to protect you during the two-
to four-week period before antibodies (proteins from your immune
system that protect you from the flu virus) develop or when a flu
epidemic is caused by virus strains other than those covered by
What is the Treatment for the Flu?Many people treat their
flu infections by simply
not give aspirin to children and adolescents who have the
- Resting in bed
- Drinking plenty of fluids
- Taking over-the-counter medicine such as aspirin or
acetaminophen (Tylenol®, for example)
You should not take antibiotics to
treat the flu because they do not work on viruses. Antibiotics only
work against some infections caused by
If you do get the flu and want to
take medicine to treat it, your doctor may prescribe one of four
available antiviral medicines:
To work well, you must take these medicines
within 48 hours after the flu begins. They reduce the length or time
fever and other symptoms last and allow you to return to your daily
- Tamiflu® (oseltamivir) helps adults 18 years
and older and Relenza® (zanamivir) helps adults
and children 7 years and older who have an uncomplicated flu
infection and who have had symptoms for no more than two days. FDA
recently approved Tamiflu® for use in children 1 year of age and
older who have had symptoms for no more than two days. Both treat
influenza type A and type B infections.
- Flumadine® (rimantadine) helps adults who
have influenza type A virus infections. It has no effect on
influenza type B virus infections.
- Symmetrel® (amantadine) can be taken by
adults and children who are 1 year of age and older to prevent and
treat type A or type B influenza virus infections. Amantadine,
however, is more likely to cause side effects such as
lightheadedness and inability to sleep more often than is
What are Possible Complications from the Flu?You can have
flu complications if you get a bacterial infection, which causes
pneumonia in your weakened lungs. Pneumonia also can be caused by
the flu virus itself.
Symptoms of complications will usually
appear after you start feeling better. After a brief period of
improvement, you may suddenly get
Pneumonia can be a very serious and sometimes
life-threatening condition. If you have any of these symptoms, you
should contact your doctor immediately so that you can get the
- High fever
- Shaking chills
- Chest pain with each breath
- Coughing that produces thick, yellow-greenish-colored mucus
Are There Other Flu Complications that Only Affect
Children?Reye's syndrome, a condition that affects the nerves,
sometimes develops in children and adolescents who are recovering
from the flu. Reye's syndrome begins with nausea and vomiting, but
the progressive mental changes (such as confusion or delirium) cause
the greatest concern.
The syndrome often begins in young
people after they take aspirin to get rid of fever or pain. Although
very few children develop Reye's syndrome, you should consult a
doctor before giving aspirin or products that contain aspirin to
children. Acetaminophen does not seem to be associated with Reye's
Other complications of the flu that affect children
recently out of intensive care units are particularly vulnerable to
suffering from flu complications.
- Convulsions caused by fever
- Ear infections, such as otitis media
Are There Different Types of Flu Viruses?The first flu
virus was identified in the 1930's. Since then, scientists have
classified flu viruses into types A, B, and C.
Type A is the
most common and usually causes the most serious epidemics. Type B
outbreaks also can cause epidemics, but the disease it produces
generally is milder than that caused by type A. Type C viruses, on
the other hand, never have been connected with a large epidemic.
Flu Pandemics in the 20th CenturyIf a flu virus emerges
that is either new or that has not circulated in many years, and if
it is able to spread easily from person to person, it could quickly
travel around the world and cause serious illness and death for
millions of people. This is called a flu pandemic.
Spanish flu pandemic is the catastrophe against which all modern
pandemics are measured. More than 20 million people were killed
worldwide; 500,000 died in the United States alone. This virus was
especially quick to kill. So far, the world has not seen a virus
that severe again.
In 1957 and 1968, the Asian flu and Hong
Kong flu, respectively, invaded the United States. Although hundreds
of thousands of people in the United States died, the death toll for
each pandemic was not as high as that for the Spanish flu
In 1976, the United States experienced a swine flu scare.
When a new flu virus was first identified at Fort Dix, New Jersey,
it was labeled the "killer flu," and health experts were afraid that
it would infect people around the world. In fact, swine flu never
left the Fort Dix area. Research on the virus later showed that if
it had spread, it would probably have been much less deadly than the
In 1997, another "near miss" pandemic occurred
when 18 people in Hong Kong became ill from a new flu virus. Six of
the infected people subsequently died. Usually, flu viruses move
first from chickens to pigs, and then from pigs to humans. This
virus was different because it moved directly from chickens to
people. The avian flu never became a pandemic, however, because it
didn't easily spread from person to person. In addition, public
health authorities ordered the slaughter of all live chickens in
What Research is Going On?Although flu epidemics pop up in
the fall and winter seasons in communities throughout the world
every year, including the United States, there has not been a
pandemic since 1968. Scientists are worried that a new flu virus
will emerge in the 21st century and cause a severe pandemic again.
For this reason, research institutions and health departments around
the world are cooperating to track flu outbreaks in humans and
animals, and to determine what types and strains of flu viruses are
Keeping on Top of Your Condition
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Where Can I Get More Information About the Flu?
- National Institute on Aging
- Centers for Disease Control and
- Food and Drug Administration