Influenza, or flu, is a respiratory infection. The most familiar aspect
of the flu is the way it can "knock you off your feet" as it
sweeps through entire communities.
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.
The Centers for Disease Control and Prevention (CDC) estimates 5 to 20
percent of 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 200,000 people are hospitalized
and about 36,000 people die from the flu and its complications every year.
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 3 weeks and subsides
after another 3 or 4 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 family members infected
Importance of flu
In addition to the rapid start of the outbreaks and the large number
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 life-threatening.
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 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.
If you get infected by the flu virus, you will usually feel symptoms 1 to
4 days later. You can spread the flu to others before your symptoms start
and for another 3 to 4 days after your symptoms appear. The symptoms start
very quickly and may include
- Body aches
- Dry cough
- Sore throat
- Stuffy nose
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 call "stomach flu" is not influenza.
You can have flu complications if you get a bacterial infection, which can
cause pneumonia in your weakened lungs. Pneumonia also can be caused by
the flu virus itself.
Complications usually appear after you start feeling better. After a
brief period of improvement, you may suddenly get these symptoms
- High fever
- Shaking chills
- Chest pain with each breath
- Coughing that produces thick, yellow-greenish-colored mucus
Pneumonia can be a very serious and sometimes life-threatening condition.
If you have any of these symptoms, you should contact your health care
provider immediately to get the appropriate treatment.
Flu complications in children and teenagers
Reye's syndrome, a condition that affects the nerves, sometimes develops
in children and teenagers 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 health care provider before giving aspirin or products
that contain aspirin to children. Acetaminophen does not seem to be connected
with Reye's syndrome.
Other complications of the flu that can affect children are
- Convulsions caused by fever
- Ear infections, such as otitis media
Newborn babies recently out of intensive care units are particularly
vulnerable to suffering from flu complications.
Usually, health care providers diagnose the flu on the basis of whether
it is epidemic in the community and whether the person's complaints fit
the current pattern of symptoms. Health care providers 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.
Many people treat their flu by simply
- Resting in bed
- Drinking plenty of fluids
- Taking over-the-counter medicine such as aspirin or acetaminophen
(Tylenol, for example)
Medicine for Treatment
If you do get the flu and want to take medicine to treat it, your health
care provider may prescribe an antiviral medicine.
- Tamiflu (oseltamivir) is for treating influenza A and B virus infections
in adults and children 1 year and older.
- Relenza (zanamivir) is for treating influenza A and B virus infections
in children 7 years and older and adults who have an uncomplicated flu
infection and who have had symptoms for no more than 2 days.
To work well, you must take these medicines within 48 hours after the
flu begins. They reduce the length of time fever and other symptoms last
and allow you to more quickly return to your daily routine.
NOTE: Because of influenza A virus resistance to rimantadine and amantadine,
CDC currently recommends that you not take these medicines to treat the
Do not give aspirin to children and adolescents who have the flu.
Do not take antibiotics to treat the flu because they do not work on
viruses. Antibiotics only work against some infections caused by bacteria.
Prevention / Risk Factors
Flu is caused by a variety of influenza viruses. Researchers identified
the first virus in the 1930s. Since then, they have classified influenza
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.
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 have been killed, they cannot infect
you. 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 on types of flu viruses) expected to circulate the following
Sometimes, an unpredicted new strain may appear after the vaccine has
been made and distributed to doctors' offices 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 will still give you some protection.
Your immune system takes time to respond to the flu vaccine. Therefore,
you should get vaccinated every year in October or November to prevent
getting infected or reduce the severity of the flu if you do get it. Because
the flu season usually lasts until March, however, it's not too late to
get it after the season has begun. 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 vaccinated.
Until recently, you could get the flu vaccine only as an injection (shot).
In 2003, however, the Food and Drug Administration (FDA) approved a nasal
spray flu vaccine called FluMist that you can get from your health care
provider. FDA approved it for use in healthy people aged 5 to 49 years
who are not pregnant.
Because the flu vaccine can cause problems, or side effects, in some
people, CDC recommends you talk with your health care provider before
getting a flu vaccine shot or nasal spray flu vaccine.
Possible side effects
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 2 days.
Viruses for 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 if you are allergic to eggs.
If you are in any of the following groups or live in a household with
or provide care for someone who is, CDC recommends that you get the flu
- 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 3 months pregnant during the flu season
- You live in a nursing home or other chronic-care housing facility
- You are in close contact with infants or children up to 5 years of
CDC recommends children from age 6 months up to their fifth birthday
get the flu vaccine.
Medicine for Prevention
Although the flu vaccine is the best way to prevent getting the flu,
two antiviral medicines also are available by prescription that will help
prevent flu infection-Tamiflu (oseltamivir) and Relenza (zanamivir).
- These medicines help prevent the flu if you take them for at least
2 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
- You may use them immediately following flu vaccination during a flu
epidemic to protect you during the 2- to 4-week period before antibodies
develop or when a flu epidemic is caused by virus strains other than
those covered by the vaccine. (Antibodies are proteins from your immune
system that protect you from the flu virus.)
NOTE: Because of influenza A virus resistance to rimantadine
and amantadine, CDC currently recommends that you not take these medicines
to prevent flu.
Your health care provider can help you decide which medicine is best
for you. You should discuss the flu vaccine and medicines with your health
care provider before the flu season begins.
Good health habits are also important to help prevent the flu.
- Wash your hands often to help protect you from germs.
- Avoid close contact with people who are sick, if possible.
- Keep your distance from others when you are sick, to protect them
from becoming infected.
- Stay home from work, school, and errands when you are sick, if possible,
to help prevent others from catching your illness.
- Cover your mouth and nose with a tissue when coughing or sneezing.
- Keep your hands away from your eyes, nose, or mouth. Germs are often
spread when you touch something that is contaminated with them and then
touch your eyes, nose, or mouth.