Influenza (the flu) — Questions & Answers
What
is influenza (the flu)?
Influenza,
commonly called "the flu," is caused by the influenza virus,
which infects the respiratory tract (nose, throat, lungs). The flu usually
spreads from person to person when an infected person coughs, sneezes,
or talks and the virus is sent into the air. Unlike many other viral respiratory
infections, such as the common cold, the flu causes severe illness and
life-threatening complications in many people.
What
are the symptoms of the flu?
Influenza
is a respiratory illness. Symptoms of flu include fever, headache, extreme
tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches.
Children can have additional gastro-intestinal symptoms, such as nausea,
vomiting, and diarrhea, but these symptoms are uncommon in adults. Although
the term "stomach flu" is sometimes used to describe vomiting,
nausea, or diarrhea, these illnesses are caused by certain other viruses,
bacteria, or possibly parasites, and are rarely related to influenza.
Does
the flu have complications?
Yes. Some
of the complications caused by flu include bacterial pneumonia, dehydration,
and worsening of chronic medical conditions, such as congestive heart
failure, asthma, or diabetes. Children may get sinus problems and ear
infections as complications from the flu. Those aged 65 years and
older and persons of any age with chronic medical conditions are at highest
risk for serious complications of flu.
How
do I find out if I have the flu?
It is very
difficult to distinguish the flu from other viral or bacterial causes
of respiratory illnesses on the basis of symptoms alone. A test can confirm
that an illness is influenza if the patient is tested within the first
two to three days after symptoms begin. In addition, a doctor's examination
may be needed to determine whether a person has another infection that
is a complication of influenza.
How
soon will I get sick if I am exposed to the flu?
The time
from when a person is exposed to flu virus to when symptoms begin is about
one to four days, with an average of about two days.
How
long is a person with flu virus contagious?
The period
when an infected person is contagious depends on the age of the person.
Adults may be contagious from one day prior to becoming sick and for three
to seven days after they first develop symptoms. Some children may be
contagious for longer than a week.
| Preventing
and Treating the Flu |
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What
can I do to protect myself against the flu?
By far,
the single best way to prevent the flu is for individuals, especially
persons at high risk for serious complications from the flu, to get a
flu shot each fall.
Who
should get a flu shot?
The
most important groups of
persons who should get flu shots are those who are at highest risk for
developing serious complications from the flu.
Can
antiviral drugs cure the flu?
Not exactly.
When started within the first two days of illness, they can reduce the
duration of the disease but cannot cure it outright.
Four different
antiviral drugs (amantadine, rimantadine, zanamivir, and oseltamivir)
have been approved for treating the flu. All four drugs can reduce the
duration of flu by about one day if taken within 2 days of when symptoms
begin. The four drugs differ in terms of side effects. In some patients,
amantadine (Symmetrel®, others) can cause symptoms such as nervousness,
difficulty concentrating, or lightheadedness. Rimantadine (Flumadine®)
can also cause similar types of side effects, but less often. Caution
is advised if zanamivir (Relenza®) is used by people who have asthma or
chronic obstructive pulmonary disease, because the airways of these
people may suddenly grow smaller after using zanamivir, leading to difficulty
breathing. Oseltamivir (Tamiflu®) can cause nausea and vomiting in some
people.
All
of these drugs must be prescribed by a doctor. These drugs are effective
against flu viruses, but they are not effective against other viruses
or bacteria that can cause symptoms similar to influenza. These drugs
are not effective for treating bacterial infections that can occur as
complications of influenza.
Can
antiviral medications prevent the flu?
Three of
the antiviral drugs (amantadine, rimantadine, and oseltamivir) have been
approved for prevention of the flu. These drugs are not, however, a substitute
for influenza vaccination. All of these drugs are prescription drugs,
and a doctor should be consulted before the drugs are used for preventing
the flu.
For
More Information About
Influenza Antiviral Drugs:
"Prevention
and Control of Influenza, Recommendations of the Advisory Committee on
Immunization Practices (ACIP)," Morbidity and Mortality Weekly
Report (MMWR), April 25, 2003/ Vol. 52 / No. RR-08.
| When
You Are Most Likely to Get the Flu |
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When
is the flu season in the United States?
In the United
States, the peak of flu season can occur anywhere from late December through
March. The health impact (infections and deaths) of a flu season
varies from year to year. CDC monitors circulating flu viruses and their
related disease activity and provides influenza reports each week from
October through May. See: Weekly U.S. Flu
Report
How
many people get sick or die from the flu every year?
Each flu
season is unique, but it is estimated that approximately 10% to 20% of
U.S. residents get the flu, and an average of 114,000 persons are hospitalized
for flu-related complications. About 36,000 Americans die on average per
year from the complications of flu.
Do
other respiratory viruses circulate during the flu season?
In addition
to the flu virus, several other respiratory viruses also can circulate
during the flu season and can cause symptoms and illness similar to those
seen with flu infection. These non-flu viruses include rhinovirus (one
cause of the "common cold") and respiratory
syncytial virus (RSV), which is the most common cause of severe
respiratory illness in young children as well as a leading cause of death
from respiratory illness in those aged 65 years and older.
What
are some of the myths about flu?
There are
several common myths about flu, including:
Myth
#1:
Influenza is merely a nuisance. |
Wrong.
Influenza is a major cause of illness and death in the United States
and leads to an average of about 36,000 deaths and 114,000 hospitalizations
per year. |
Myth
#2:
Flu shots cause the flu. |
Wrong.
The licensed injectable flu vaccine used in the United States, which
is made from inactivated or killed flu viruses, cannot cause
the flu and does not cause flu illness. |
Myth
#3:
Flu vaccine doesn't work. |
Not
exactly. When the viruses in the vaccine and circulating viruses
are similar, the flu shot is very effective. There are several reasons
why people think influenza vaccine doesn't work. People who have gotten
a flu vaccination may then get sick from a different virus that causes
respiratory illness but is mistaken for flu; the flu shot only prevents
illness caused by the influenza virus. In addition, protection
from the vaccine is not 100%. Studies of healthy young adults have
shown flu vaccine to be 70% to 90% effective in preventing the flu.
In the elderly and those with certain long-term medical conditions,
the flu shot is often less effective in preventing illness. However,
in the elderly, flu vaccine is very effective in reducing hospitalizations
and death from flu-related causes. |
Myth
#4:
There is no need to get a flu vaccine every year.
|
Wrong.
The flu viruses are constantly changing. Generally, new influenza
virus strains circulate every flu season, so the vaccine is changed
each year.
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From the
National Center for Infectious Diseases
January 15, 2003
http://www.cdc.gov/ncidod/diseases/flu/facts.htm
Also see
flu shots
interim influenza vaccination recommendations (2004)
press release:
this fall protect ourself and your family: get a flu shot
what everyone should know about flu and the flu vaccine
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