Influenza
OVERVIEW
Influenza, or 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 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 that
10 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 100,000 people are hospitalized and about 36,000 people die from
the flu and its complications every year.
FLU OUTBREAKS
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 the family members
infected each year.
IMPORTANCE OF FLU
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 life-threatening.
TRANSMISSION
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.
SYMPTOMS
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
- Chills
- Dry cough
- Fever
- Headache
- 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.
DIAGNOSIS
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.
PREVENTION
Flu Vaccine
The main way to keep from getting 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
infection. 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 doctor's 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 still will give you some protection.
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, which you can get from your
health care provider. FDA approved it for use in healthy people aged 5 to 49 years.
You should not use FluMist if
- You have certain lung conditions, including asthma, or heart conditions
- You have metabolic disorders such as diabetes or kidney dysfunction
- You have an immunodeficiency disease or are on immunosuppressive treatment
- You have had Guillain-Barré syndrome
- You are pregnant
- You have a history of allergy or hypersensitivity, including anaphylaxis,
to any of the parts of FluMist or to eggs
Children or teenagers who regularly take aspirin or products containing
aspirin also should not take FluMist.
Your immune system takes time to respond to the flu vaccine. Therefore,
you should get vaccinated 6 to 8 weeks before flu season begins in November
to prevent getting infected or reduce the severity of 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.
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. 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 health care provider before getting vaccinated.
Vaccine recommendations
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.
- 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 children 0 to 23 months of age
| Due to the flu vaccine shortage of 2004-2005, CDC, in coordination
with its Advisory Committee for Immunization Practices (ACIP), is
issuing interim recommendations for influenza vaccination for the
2004-2005 season. Go to this Web site for the 2004-2005 recommendations:
http://www.cdc.gov/flu/protect/whoshouldget.htm.
In addition, the ACIP has recommended that the U.S. government's
Vaccines for Children program expand its distribution of FluMist to children
and adolescents aged 5 to 18 for the 2005-2006 season. |
CDC recommends that children 6 months to 23 months of age get the flu vaccine.
Children and teenagers (2 to 18 years of age) 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 groups.
Health care providers and volunteers should get the flu vaccine if
they work with people in any of the above groups.
Medicine for Prevention
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.
- Tamiflu (oseltamivir)
- Flumadine (rimantadine)
- Symmetrel (amantadine)
Tamiflu is for use in adults and teenagers 13 years and older. Rimantadine
and amantadine may be used by adults and children who are 1 year of
age and older.
- 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 the flu
- You may use either medicine immediately following flu vaccination
during a flu epidemic to protect you during the 2- to 4-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 the vaccine
Flumadine and Symmetrel have unpleasant side effects. 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.
TREATMENT
Many people treat their flu infections by simply
- Resting in bed
- Drinking plenty of fluids
- Taking over-the-counter medicine such as aspirin or acetaminophen
(Tylenol, for example)
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.
Medicine for Treatment
If you do get the flu and want to take medicine to treat it, your health
care provider may prescribe one of four available antiviral medicines.
- Tamiflu (oseltamivir) is for adults and children 1 year and older
and Relenza (zanamivir) is for adults and children 7 years and older
who have an uncomplicated flu infection and who have had symptoms
for no more than 2 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) may be taken by adults and children who are
1 year of age and older to prevent and treat type A influenza virus
infections. Symmetrel, however, is more likely to cause side effects
such as lightheadedness and inability to sleep more often than is Flumadine.
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 return to your daily routine quicker.
FLU COMPLICATIONS
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 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
- Croup
- Ear infections, such as otitis media
Newborn babies recently out of intensive care units are particularly
vulnerable to suffering from flu complications.
TYPES OF FLU VIRUSES
The first flu virus was identified in the 1930s. 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
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