Where Does Fever Come From?
How Do
I Measure Temperature?
What
Should I Worry About? When Should I Call My Doctor?
What
Other Symptoms Typically Accompany Fever?
What
Types of Illnesses Cause Fever, and What Are Their Specific Symptoms?
How Do
I Treat Fever?
Is
There a Downside to Treating a Fever?
What
Might the Doctor Do?
How Do I
Prevent Fever?
Fever in
children can provoke tremendous anxiety in parents. Children with
fever are hot, sweaty, flushed, and fussy. In healthy children,
however, fevers rarely indicate serious illness. In fact, fever is a
way your child’s body actually fights infections. It
is not even necessary always to treat fever in children. High
fevers, however, make children increasingly uncomfortable and may cause
irritability and dehydration.
Normal body temperature is usually cited
as 98.6 degrees Fahrenheit, as measured by a thermometer placed under the
tongue (“oral temperature”). “Normal” temperature varies in children
by 1-1.5 degrees throughout the day and according to their level of activity;
it is usually lowest early in the morning and highest in late
afternoon. Fever is an elevation of body temperature
above that normal range. Fever is defined as a rectal temperature greater than
100.4 degrees Fahrenheit, an oral temperature greater than 99.5 degrees
Fahrenheit, or an axillary temp greater than 99 degrees
Fahrenheit. Children under 2 months of age should always be
evaluated by a physician for temperature above 100.4 degrees measured
rectally. Fever is the human body’s normal and healthy reaction to
infection and is caused by a complex chain of biochemical and cellular
reactions that are launched to fight that infection. Elevation of a
child’s body temperature associated with active play or with exposure to hot weather
is not considered a fever.
Fever is a symptom, not a disease. The magnitude of fever does not
necessarily correlate to the severity of infection, as fever may be very high with a brief viral illness and lower (or sometimes the body temperature is actually abnormally low) in the face of a life-threatening infection. It is generally felt that a fever up to around 102 degrees Fahrenheit (oral) can help the body fight the infection, although as stated above this does not apply to children under two months of age In general, children have higher fevers than adults (1). This Knol discusses fever in children; fever in adults is discussed separately.
Body
temperature is controlled by a small organ deep in the brain called thehypothalamus (FIGURE
1). The hypothalamus controls metabolic processes in the body (such
as body temperature, hunger, thirst, fatigue, and stress reactions) by
releasing tiny amounts of chemicals that act on other body organs either directly
or indirectly. With respect to body temperature, the hypothalamus
acts as a thermostat; it helps maintain body warmth when someone is exposed to
cold temperatures by causing shivering and an increased metabolic
rate. When a child is hot (from a fever, from exercise, or from hot
weather), it causes sweating and dilation (opening up) of blood vessels in the
skin, allowing dissipation of heat.
Fever
results when the hypothalamus detects the presence of pyrogens, or
fever-inducing substances. Pyrogens are usually foreign substances to your
child’s body, such as bacteria, viruses, parasites, immunizations, or
toxins. The presence of these pyrogens activates other “native” (not
foreign) infection-fighting pyrogens such as white blood cells inside the body,
and the accumulation of these substances signals the hypothalamus to raise the
temperature on the body’s thermostat. In response, the child feels
cold and his body shivers, blood vessels in the skin constrict (tighten down)
to retain heat, and he seeks warm clothing or bed covers, all in an attempt to
reach the new target temperature on the thermostat. That new, higher
temperature represents a higher metabolic level for the body, assisting the
child’s fight against the infection.
Once
the higher temperature is reached, the child begins to feel
hot. Clothing and bed covers are shed, and the temperature begins to
drop back towards normal. The child may begin to sweat and the blood
vessels in the skin dilate, leading to rosy cheeks and release of
heat. Fever medications, also called “anti-pyretics” such as
acetaminophen and ibuprofen, work by interfering with the function of the
hypothalamus. These drugs therefore inhibit the body’s natural
response to infection (see “Is There a Downside to Treating a Fever?,”
below).
How Do I Measure Temperature?
Body
temperature can be measured by glass thermometers or plastic analog or digital
thermometers placed under the tongue (oral), into the rectum (rectal), or into
the armpit (axillary) with the arm held tightly against the
torso. There are also digital thermometers that measure temperature
inside the ear (tympanic), plastic strip thermometers that measure the
temperature on the forehead, and pacifier thermometers that measure an
above-the-tongue oral temperature. Axillary temperatures are not
considered reliable by physicians, but may give caregivers an idea of the
magnitude of fever if they are uncomfortable obtaining a rectal
temperature. In very young children, particularly infants in whom an
accurate temperature reading is important, tympanic, forehead, and pacifier
temperature are not optimal. Rectal temperature is closer to the
body’s true “core” temperature. Generally, rectal temperatures are
preferred in children under 2-3 years of age; oral temps are preferred
thereafter.
Rectal temps are obtained by inserting a
petrolatum-coated thermometer about a half-inch inside the rectum; stop if any
resistance is felt. Hold the rectal thermometer there until the temperature
is taken; depending on the thermometer, this may take only a few seconds or as
long as a couple of minutes. If the child is moving, it is important
to hold the thermometer between the second and third fingers, with the hand
resting on the buttock, so that the probe doesn’t go too deep if the child
squirms (FIGURE 2). Oral temperature is measured by placing the
thermometer under the tongue, and holding it there for 2-3 minutes (or until a
digital thermometer signals that it is ready) without talking and preferably
while breathing through the nose; this may be difficult in a child who is
coughing or who is mouth-breathing because of nasal congestion. Avoid
measuring oral temperature within 15 minutes after drinking a hot or cold
beverage, or just after a bath. Rectal temperatures are always about one
degree higher than oral temps, and a fever is defined as a rectal temperature
greater than 100.4 degrees Fahrenheit, an oral temperature greater than 99.5
degrees Fahrenheit, or an axillary temp greater than 99 degrees
Fahrenheit.
If
no thermometer is available, feeling the skin temperature on the forehead or
the side of the neck may give a relative sense of whether or not fever is
present. Flushing of the skin, shaking chills, fatigue, perspiration,
and lethargy or fussiness often accompany fever and may be suggestive in the
absence of actual temperature measurement.
What Should I Worry About? When Should I Call My Doctor?
Children
under 2 months of age should be evaluated by a physician for any
fever. Older children should be evaluated by a physician for a
temperature higher than 102.2 degrees Fahrenheit, or when fever is accompanied
by one of the following conditions:
- seizure
- inconsolable
crying or irritability
- rash or purple spots that look like bruises on the
skin (FIGURE 3, photo reproduced with permission of Annals of
Emergency Medicine)
- bluish tinge around the lips or finger- and toenails
- stiff neck
or severe headache
- difficulty breathing that does not improve after clearing the nose
- leaning
forward and drooling
- persistent
vomiting or diarrhea
- signs of dehydration (small amounts or no urination, no tears when
crying, listless or drowsiness) and not taking oral fluids well
- a specific, localized complaint, such as an earache, sore throat,
abdominal pain, or pain with urination
- in infants, a swelling or noticeable sinking of the soft spot at
the top of the head
- sore or
swollen joints
- fever developed after child was left in a very hot environment,
including an automobile
- fever that persists for more than 24 hours in children 2 mos-2
years of age, or for more than 72 hours in children over 2, or fever that
comes and goes over several days
In the absence of these conditions, and in
children who are fully vaccinated and do not have chronic health problems,
parents can try to manage fever at home with antipyretics, rest, and hydration.
What Other Symptoms Typically Accompany Fever?
Physicians
often determine the approach to fever based on the child’s
age. There are three age groups with respect to the concern
physicians have for a fever: age 1-30 days, age 1-24 months, and age greater
than two years (2,3). Neonates (a term used for patients less
than one month of age) have very immature immune systems and are exposed to a
variety of infections uncommon in older children. Children more than
one month but less than two years old may require a more intensive evaluation
for fever than older children. Beyond age two, children increasingly
resemble adults in terms of the fevers they develop in response to exposure to
infections, drugs, and toxins.
Common general symptoms accompanying a
fever in children include flushing/redness, profuse perspiration, irritability,
fatigue, and lethargy. More so than in adults, the rate at which the
temperature rises in ill children is as important as the actual height of the
fever. In fact, “febrile seizures”--seizures due to rapid rise in
body temperature that typically occur in children between the ages of 6 months
and 3 years--appear to be related primarily to the fast rise of
temperature. About 4% of children under the age of 5 suffer a
febrile seizure; usually no specific treatment (other than fever control) is
required for these children (2). The symptoms accompanying
fever--whether as dramatic as a seizure or as nonspecific as flushing--give
physicians clues to the source of the illness and the need and urgency for
specific treatment.
What Types of Illnesses Cause Fever, and What Are Their Specific Symptoms?
The
most common source of fever in otherwise healthy children is a viral
infection (2). Viruses can cause croup, bronchiolitis (caused
by respiratory syncitial virus or “RSV”) and other “URIs,” or upper respiratory
infections, sore throat, nasal congestion or runny nose, cough, and muscle
aches (4). Other viruses cause gastrointestinal illnesses,
marked by fever, nausea with or without vomiting, diarrhea, abdominal pain, and
malaise. Chicken pox is caused by the varicella virus, and in
addition to typical skin lesions, may occasionally cause pneumonia in
children. Normally, such viral illnesses resolve on their own, over
time (they may last as long as a week or two), with what physicians call
“supportive care.” Supportive care includes rest, lots of noncaffeinated
fluids to drink, and over-the-counter medications such as cough syrup,
decongestants, or acetaminophen. Viral infections by definition do
not improve with antibiotics, and in fact children with viral illness who are
treated with antibiotics may end up feeling worse than they did before therapy.
There
are, of course, more serious viral infections. Influenza is caused
by a virus and can be a significant source of illness and even death,
especially in the very young or chronically ill child. Other important
viruses that can cause fever in children include mononucleosis (which infects
the lymph glands and spleen), hepatitis (liver), viral meningitis (fluid around
the brain and spinal cord), and viral encephalitis (brain). Although
fever is nearly always present with one of these serious illnesses, other
symptoms typically cause more concern and prompt consultation with a
physician. Viral illnesses also make children who have asthma more
likely to have wheezing and breathing difficulty.
A
low-grade fever (less than 101 degrees Fahrenheit) may be associated with
teething. This probably results from inflammation of the gums as the
teeth erupt, and not from an actual infection. Teething fever
resolves with acetaminophen and the child can be made more comfortable with
cold liquids or popsicles. Infants may develop low-grade fevers from
overdressing, sometimes called “overbundling.” The hypothalamus of a newborn is
not as efficient as that of older children, so they sometimes do not regulate
their body temperature effectively. Parents should avoid
overbundling, but should also not keep infants uncovered to the extent that the
child shivers.
Bacterial
infections can occur in most organs and tissues in the body and are usually
more serious than viral illnesses, even though most are easily treatable with
antibiotics. Fever is a typical feature of bacterial
infections. Fever associated with a bacterial infection of the
central nervous system (brain and spinal cord) such as meningitis is typically
accompanied by headache, stiff neck, and changes in behavior such as lethargy
or confusion. These symptoms should prompt urgent consultation with
a physician. In children, the middle ear is particularly prone to
infection by both bacteria and viruses (5). This is called
“otitis media.” Very young children may not be able to express the
symptoms of a painful ear, but parents may notice a child--particularly one
that has recently had a cold--pulling or tugging at one of his ears. The
skin, which is the largest organ of the body, can be infected by
bacteria. Usually there is a clear point of bacterial entry, such as
a cut or scrape. Skin infections are characterized by fever accompanied by
pain, redness, swelling, and warmth. Sometimes pus drains from the
area. Antibiotics are used to treat such illnesses, which are called
“cellulitis” (6).
The
respiratory and gastrointestinal tracts are common locations for bacterial
infections that cause fever. Bronchitis and pneumonia cause cough
and difficulty breathing in addition to fever, while gastrointestinal
infections are associated with fever, abdominal pain, loss of appetite,
vomiting, and/or diarrhea. Urinary tract infections may cause fever,
flank pain, nausea and vomiting, and burning and frequent
urination. The bottom line about bacterial infections is that,
although fever is often part of the general illness, there are specific
symptoms that can direct a caregiver to a specific cause and thence to specific
antibacterial therapy.
Another
common cause of fever in children is immunizations. Fever is common
within a few hours of administration of the diphtheria-tetanus-pertussis (DTP)
vaccine, and it may persist (along with fussiness) for a couple of days. Fever
may also occur after the administration of vaccines containing live viruses,
such as the measles-mumps-rubella (MMR) vaccine, although often not until 7-10
days after the shot. Treatment with acetaminophen or ibuprofen is
effective. Overall immunization status is also important when a
child is evaluated by a physician for fever; the physician will want to know if
the child has received pneumococcal, H.flu, and hepatitis vaccines because if
the child is not up-to-date on these immunizations, the likelihood of serious
illness underlying a high fever or other manifestations of severe illness may
be greater. It is also important to note that sometimes a very
serious bacterial infection in children will cause the body temperature to
be lowerthan normal.
Fever
in children can be treated with acetaminophen or ibuprofen. Aspirin
is not recommended because of its association with a rare but potentially fatal
liver disease called Reye’s syndrome in some children with viral
illnesses. Both acetaminophen and ibuprofen can also help reduce the
aches, pains, and fussiness that often accompany fever. The dosing
of acetaminophen and ibuprofen for fever is based on your child’s age and
weight. Acetaminophen (Tylenol®, Panadol®, Feverall®, etc.) comes in
syrups, chewable tablets, and pills for swallowing; it can be given every four
hours as need. Ibuprofen (Advil®, Motrin®, Nuprin®, etc.) also comes
in a variety of formulations and can be given to children every six
hours. It may be beneficial to alternate or even combine
acetaminophen and ibuprofen when children have especially high fevers or feel
very ill with their fever. Children younger than two months of age with a
fever should always be evaluated by a physician.
General
treatment measures that might reduce an elevated body temperature and make the
patient feel better overall include rest, oral hydration (with Pedialyte®,
Gatorade®, or other rehydration fluids), and over-the-counter medications for
specific fever-related symptoms, such as decongestants, cough remedies, or
anti-diarrhea medications. A sponge bath may make the child feel
better, but it is important to use lukewarm--not cold--water, so as not to
cause shivering, which raises body temperature. Alcohol sponge baths
are not recommended, nor are ice packs or cold baths.
If
a child experiences a febrile seizure, try to lay the child on his or her side
and protect the child from falling or from injury from any nearby
objects. Febrile seizures typically do not last more than a couple
of minutes, but to the parent observing it, it may seem to last much
longer. If possible, grab a watch and time the duration of the
seizure activity, during which the child will typically shake and not be
responsive to your words or physical comforting. Don’t put anything
in the child’s mouth and don’t do anything to try to stop the
seizure. Simply protect the child from falling or otherwise hurting
himself or herself. A child who has had a febrile seizure should be
evaluated in an emergency department as soon as possible.
Although
fevers in their children make parents anxious, low-grade fevers in healthy
children don’t necessarily require aggressive treatment. The illness
underlying a fever in a child is probably not serious if the child remains
playful, is eating and drinking, is alert and normally interactive with
parents, and feels better when the temperature comes down.
Ill
children--even those with mild viral sicknesses--often experience a decreased
appetite. The child should generally be allowed to eat what he or
she wants, in small amounts, and forced feedings are not
necessary. More attention should be paid to providing ample liquids
and encouragement for drinking. Children with fever should generally
be kept out of school and daycare settings. Generally it is safe to
return to such activities when the child’s temperature has been normal for 24
hours.
Is There a Downside to Treating a Fever?
This
is an intriguing question for which the answer is not entirely
clear. What is known is that the answer varies by type of
illness. Acetaminophen and aspirin do not prolong the duration of a
URI in adults, although they do appear to prolong the duration of the
contagious interval and may worsen nasal congestion. In a small
study, acetaminophen did not impact the overall condition of children with
chicken pox, but it did prolong the time until scabbing over of lesions
(chicken pox is considered contagious until all lesions are scabbed over). Another
study seemed to indicate that patients with influenza A treated with
antipyretics had longer courses of illness than those who were not treated,
although it also appeared that it was sicker patients--with higher fevers--who
took the acetaminophen, so it may be that those patients were destined to
remain ill longer, anyway. What has not been studied well is the
balance between symptomatic relief--i.e., reduction of the fever itself--and
duration of illness; that is, even if patients are ill a day or two longer, do
they feel better sooner with the fever treatment? The thinking
behind this question is that, if fever is a natural response to infection, and
if the higher metabolic rate associated with fever helps the body fight
infection, should we try to suppress fever and interfere with that immune
response? The viruses that cause URIs, for example, seem to thrive
at cool temperatures. In summary, however, available data at the
present time suggest that there is little if any significant downside to the
use of antipyretic medications in patients with fever associated with acute
illness(7).
As
noted, children under 2 months of age should be evaluated by a physician for
any fever. Older children should be evaluated by a physician for a
temperature higher than 102.2 degrees Fahrenheit, or when fever is accompanied
by one of the symptoms listed in What Should I Worry
About? When Should I Call My Doctor? If you have
any doubt as to whether your child’s fever, or general condition, is critical,
call your doctor to see whether you should bring the child in for an
exam.
The physician’s first and primary goal in
assessing and managing fever is to make certain that the child does not have a
life-threatening illness (8). The types of very serious
infections that are typically marked by very high fever include meningitis,
pneumonia, bacteria in the bloodstream (called bacteremia), and appendicitis or
other intra-abdominal infection. The physician will first take a
history of the patient’s possible exposure to pyrogens. Has the
patient been in close proximity to another ill child or adult with a
fever? Is the child chronically ill (9)? Has he
recently received a vaccination? Is he in school or daycare?
Next,
a thorough history of the fever itself will be sought. How high has
the temperature been? Does it stay elevated despite the use of
acetaminophen or ibuprofen? How many days has the fever been
present?
The physician’s next focus is on the
patient’s other, non-fever, symptoms. Symptoms that prompt immediate
concern and thorough evaluation include new rashes, headache, stiff neck,
persistent vomiting and/or diarrhea, and coughing or wheezing that makes
breathing difficult. What was the time course of these
symptoms? Did their appearance precede or follow the development of
fever? Are these symptoms getting worse? Are there sweats
associated with the fever, and do these occur throughout the day or only at
night? The answers to these questions help guide the physician’s thinking;
if the fever is high (>101.6 degrees Fahrenheit), generalized symptoms
(aches, pains, malaise, fatigue) are not prominent, and the specific complaints
are limited to the throat, chest, or abdomen, then bacterial infection is
relatively more likely and antibiotics may be needed. If the fever
is lower (100.4-101.5 degrees Fahrenheit), systemic complaints are more
prominent, and specific complaints are less apparent, then a viral illness is
relatively more likely and antibiotics are not expected to be helpful.
A
thorough physical examination will be performed to try to find the source of
the fever. If after these questions and examination the cause of the
fever has not been definitely identified, then any of a wide variety of tests may
be conducted. These may include blood tests to determine the
intensity of the body’s response to infection; culture samples of the throat,
sputum, urine, or mucous and fluids from other sources; x-rays, including such
tests as CAT scans; urine tests; and lumbar puncture (“spinal
tap”) (FIGURE 4). These tests not only confirm the presence of
absence of infection but may also assist the physician in choosing a specific
therapy beyond treatment of fever. Such therapy may include
antibiotics, but it is important to remember that the majority of
fever-associated illnesses in children are caused by viruses, for which
antibiotic therapy is not helpful. Infants less than two months of
age with fever are frequently kept in the hospital for ongoing observation and
intravenous (into a vein) antibiotics. Young children, from 2
months-2 years of age, may be sent home pending the results of various culture
tests for bacterial infections, but often only after an intramuscular (into the
muscle of the thigh or buttock) injection of a strong antibiotic, the effects
of which last 24 hours or more; children so treated will ordinarily be brought
back to the doctor’s office or emergency department for re-evaluation (and
possibly another injection) the next day, until a final diagnosis is
determined (8).
How Do I Prevent Fever?
Illnesses
associated with fever are common in children between 2 months of age and
middle-school age. The vast majority of these illnesses are not
serious, and children are back to normal within a few days. To some
extent, illnesses that cause fever can be avoided by good parenting:
encouragement of hand-washing (by both the children and the adults who care for
them), keeping kids with fever out of school and daycare, and keeping immunizations
up to date.
References
1. Carson SM: Alternating
acetaminophen and ibuprofen in the febrile child: examination of the evidence
regarding efficacy and safety. Pediatr Nurs 2003;29:379-82.
2. Ishimine P: The evolving
approach to the young child who has fever and no obvious source. Emerg
Med Clin N Am 2007;25(4):1087-1115.
3. Ishimine P: Fever without
source in children 0 to 36 months of age. Pediatr Clin N Am 2006;53(2):167-94.
4. Shah S: Pediatric
respiratory infections. Emerg Med Clin N Am 2007;25(4):961-79.
5. Powers JH: Diagnosis and
treatment of acute otitis media: Evaluating the evidence. Infect
Dis Clin N Am2007;21(2):409-26.
6. Lopez FA: Skin and soft
tissue infections. Infect Dis Clin N Am 2006;20(4):759-72.
7. Hudgings L, Safranek S: Do
antipyretics prolong febrile illness? J Fam Pract 2005;53:57-61.
