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Normal body temperature varies from person to person and throughout the day (it is typically highest in the afternoon). Normal body temperature is higher in preschool-aged children and highest at about 18 to 24 months of age. However, despite these variations, most doctors define fever as a temperature of 100.4° F (about 38° C) or higher when measured with a rectal thermometer (see How to Take A Child's Temperature).
Although parents often worry about how high the temperature is,
the height of the fever does not necessarily indicate how serious the
cause is. Some minor illnesses cause a high fever, and some serious
illnesses cause only a mild fever. Other symptoms (such as difficulty
breathing, confusion, and not drinking) indicate the severity of illness
much better than the temperature does. However, a temperature over 106°
F (about 41° C), although quite rare, can itself be dangerous.
Fever can be useful in helping the body fight infection. Some
experts think that reducing fever can prolong some disorders or possibly
interfere with the immune system's response to infection. Thus,
although a fever is uncomfortable, it does not always require treatment
in otherwise healthy children. However, in children with a lung, heart,
or brain disorder, fever may cause problems because it increases demands
on the body (for example, by increasing the heart rate). So lowering
the temperature in such children is important.
Infants with a fever are usually irritable and may not sleep or
feed well. Older children lose their interest in play. Usually, the
higher a fever gets, the more irritable and disinterested children
become. However, sometimes children with a high fever look surprisingly
well. Children may have seizures when their temperature rises or falls
rapidly (called febrile seizures). Rarely, a fever gets so high that children become listless, drowsy, and unresponsive.
Digital Thermometer
(See also Fever in Adults.)
How to Take the Temperature in an Infant or a Child
Causes
Fever occurs in response to infection, injury, or inflammation
and has many causes. Likely causes of fever depend on whether it has
lasted14 days or less (acute) or more than 14 days (chronic), as well as
on the age of the child. Fevers are usually acute.
Acute fever
Acute fevers in infants and children are usually caused by an infection. Teething does not typically cause fever over 101° F.
The most common causes of acute fever are
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Respiratory infections due to a virus, such as colds or flu
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Gastroenteritis (infection of the digestive tract) due to a virus
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Certain bacterial infections, particularly ear infections (otitis media), sinus infections, pneumonia, and urinary tract infections
Newborns and young infants are at higher risk of certain serious
infections because their immune system is not fully developed. Such
infections may be acquired before birth or during birth and include sepsis (a serious infection of the blood), pneumonia (infection of the small air sacs of the lungs), and meningitis (infection of the tissues covering the brain).
Children under 3 years old who develop a fever (particularly if
their temperature is 102.2° F [39° C] or higher) sometimes have bacteria
in their bloodstream (bacteremia). Unlike older children, they sometimes have bacteremia with no symptoms besides fever (called occult bacteremia). Routine vaccines against the bacteria that usually cause occult bacteremia (Streptococcus pneumoniae and Haemophilus influenzae type b [Hib])
are now widely used in the United States and Europe. As a result, these
vaccines have nearly eliminated occult bacteremia in children in this
age group.
Less common causes of acute fevers include side effects of vaccinations and of certain drugs, bacterial infections of the skin (cellulitis) or joints (septic arthritis), encephalitis, and viral or bacterial infections of the brain (Kawasaki disease), the tissues covering the brain (meningitis), or both. Heatstroke causes a very high body temperature.
Typically, a fever due to vaccination lasts a few hours to a day
after the vaccine is given. However, some vaccinations can cause a fever
even 1 or 2 weeks after the vaccine is given (as with measles
vaccination). Children who have a fever when they are scheduled to
receive a vaccine can still receive the vaccine if the fever is low and
they have no serious illness.
Chronic fever
Chronic fever most commonly results from
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A prolonged viral illness
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Back-to-back viral illnesses, especially in young children
Chronic fever can also be caused by many other infectious and noninfectious disorders.
Infectious causes of chronic fever include
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Abdominal abscesses (pockets of pus in the abdomen)
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Infections of the digestive tract caused by bacteria or parasites
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Bone infections (such as osteomyelitis)
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Heart infections (such as endocarditis)
Noninfectious causes of chronic fever include
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Juvenile idiopathic arthritis or other connective tissue disorders
Occasionally, children fake a fever, or caregivers fake a fever in the child they care for. Sometimes the cause is not identified.
Evaluation
Detecting a fever is not difficult, but determining its cause can be.
Warning signs
Certain symptoms are cause for concern. They include
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Any fever in infants less than 2 months old
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Lethargy or listlessness
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Ill appearance
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Difficulty breathing
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Bleeding in the skin, appearing as tiny reddish purple dots (petechiae) or splotches (purpura)
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Continuous crying in an infant or toddler (inconsolability)
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Headache, neck stiffness, confusion, or a combination in an older child
When to see a doctor
Children with fever should be evaluated by a doctor right away if they have any warning signs or are less than 2 months old.
Children without warning signs who are between 3 months and 3
years of age should be seen by the doctor if the fever is 102.2° F (39°
C) or higher, if there is no obvious upper respiratory infection (that
is, children are sneezing and have a runny nose and nasal congestion),
or if the fever has continued more than 5 days.
For children without warning signs who are over 3 years of age,
the need for and timing of a doctor's evaluation depend on the child's
symptoms. Children who have upper respiratory symptoms but otherwise
appear well may not need further evaluation. Children over 3 years of
age with fever lasting more than 5 days should be seen by the doctor.
What the doctor does
Doctors first ask questions about the child's symptoms and
medical history. Doctors then do a physical examination. A description
of the child's symptoms and a thorough examination usually enable
doctors to identify the fever’s cause (see Table: Some Common Causes and Features of Fever in Children).
Doctors take the child’s temperature. It is measured rectally in
infants and young children for accuracy. The breathing rate is noted. If
children appear ill, blood pressure is measured. If children have a
cough or breathing problems, a sensor is clipped on a finger or an
earlobe to measure the oxygen concentration in blood (pulse oximetry).
As doctors examine children, they look for warning signs (such as
an ill appearance, lethargy, listlessness, and inconsolability), noting
particularly how children respond to being examined—for example,
whether children are listless and passive or extremely irritable.
Occasionally, the fever itself can cause children to have some of
the warning signs including lethargy, listlessness, and ill appearance.
Doctors may give children fever-reducing drugs (such as ibuprofen)
and reevaluate them once the fever is reduced. It is reassuring when
lethargic children become active and playful once the fever is reduced.
On the other hand, it is worrisome when ill-appearing children remain
ill-appearing despite a normal temperature.
Testing
For acute fever, doctors can often make a diagnosis
without testing. For example, if children do not appear very ill, the
cause is usually a viral infection; a respiratory infection if they have
a runny nose, wheezing, or a cough; or gastroenteritis if they have
diarrhea and vomiting. In such children, the diagnosis is clear, and
testing is not needed. Even if no specific symptoms suggest a diagnosis,
the cause is still often a viral infection in children who otherwise do
not appear very ill. Doctors try to limit testing to children who may
have a more serious disorder. The chance of a serious disorder (and thus
the need for tests) depends on the child's age, symptoms, and overall
appearance, plus the particular disorders the doctor suspects (see
Table: Some Common Causes and Features of Fever in Children).
If newborns (28 days old or younger) have a fever, they
are hospitalized for testing because their risk of having a serious
infection is high. Testing typically includes blood and urine tests, a spinal tap (lumbar puncture), and sometimes a chest x-ray.
In infants between 1 month and 3 months old, blood tests and urine tests (urinalysis)
and cultures are done. The need for hospitalization, a chest x-ray, and
a spinal tap depends on results of the examination and blood and urine
tests, as well as how ill or well infants appear and whether a follow-up
examination can be done. Testing in infants under 3 months old is done
to look for bacteremia, urinary tract infections, and meningitis.
Testing is necessary because the source of fever is difficult to
determine in infants and because their immature immune system puts them a
high risk of serious infection.
If children age 3 months to 3 years look well and can be
watched closely, tests are not needed. If symptoms suggest a specific
infection, doctors do the appropriate tests. If children have no
symptoms suggesting a specific disorder but look ill or have a
temperature of 102.2° F (39° C) or higher, blood and urine tests are
usually done. The need for hospitalization depends on how well or ill
children look and whether a follow-up examination can be done.
In children over 3 years of age, tests are typically not done unless children have specific symptoms suggesting a serious disorder.
For chronic fever, tests are often done. If doctors
suspect a particular disorder, tests for that disorder are done. If the
cause is unclear, screening tests are done. Screening tests include a complete blood cell count,
urinalysis and culture, and blood tests to check for inflammation.
Tests for inflammation include the erythrocyte sedimentation rate (ESR)
and measurement of C-reactive protein (CRP) levels. Other tests doctors
sometimes do when there is no clear cause include stool tests,
tuberculosis tests, chest x-rays, and computed tomography (CT) of the
sinuses.
Rarely, fevers persist, and doctors cannot identify the cause even after extensive testing. This type of fever is called fever of unknown origin. Children with a fever of unknown origin are much less likely to have a serious disorder than are adults.
Treatment
If the fever results from a disorder, that disorder is treated. Other fever treatment focuses on making children feel better.
General measures
Ways to help children with a fever feel better without using drugs include
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Giving children plenty of fluids to prevent dehydration
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Putting cool, wet cloths (compresses) on their forehead, wrists, and calves
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Placing children in a warm bath (only slightly cooler than the temperature of the child)
Because shivering may actually raise the child’s temperature, methods that may cause shivering, such as undressing and cool baths, should be used only for dangerously high temperatures of 106° F (about 41° C) and above.
Rubbing the child down with alcohol or witch hazel must not be
done because alcohol can be absorbed through the skin and cause harm.
There are many other unhelpful folk remedies, ranging from the harmless
(for example, putting onions or potatoes in the child's socks) to the
uncomfortable (for example, coining or cupping).
Drugs to lower fever
Fever in an otherwise healthy child does not necessarily require
treatment. However, drugs called antipyretic drugs may make children
feel better by lowering the temperature. These drugs do not have any
effect on an infection or other disorder causing the fever. However, if
children have a heart, lung, brain, or nerve disorder or a history of
seizures triggered by fever, using these drugs is important because they
reduce the extra stress put on the body by fever.
Typically, the following drugs are used:
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Acetaminophen, given by mouth or by suppository
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Ibuprofen, given by mouth
Acetaminophen tends to be preferred. Ibuprofen, if used for a long time, can irritate the stomach’s lining. These drugs are available over the counter without a prescription. The recommended dosage is listed on the package or may be specified by the doctor. It is important to give the correct dose at the correct interval. The drugs do not work if too little drug is given or it is not given often enough. And although these drugs are relatively safe, giving too much of the drug or giving it too often can cause an overdose.
Rarely, acetaminophen or ibuprofen is given to prevent a fever, as when infants have been vaccinated.
Aspirin is no longer used for lowering fever in children because it can interact with certain viral infections (such as influenza or chickenpox) and cause a serious disorder called Reye syndrome.
Key Points
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Usually, fever is caused by a viral infection.
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The likely causes of fever and need for testing depend on the age of the child.
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Infants under 2 months of age with a temperature of 100.4° F or higher need to be evaluated by a doctor.
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Children age 3 months to 3 years with fever who have no symptoms suggesting a specific disorder but look ill or have a temperature of 102.2° F (39° C) or higher need to be evaluated by a doctor.
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Teething does not cause significant fever.
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Drugs that lower fever may make children feel better but do not affect the disorder causing the fever.
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