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Fever in Infants and Children

by Deborah M. Consolini, MD

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.

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 (febrile seizures—see Febrile Seizures). Rarely, a fever gets so high that children become listless, drowsy, and unresponsive.

Causes

Fever occurs in response to infection, injury, or inflammation and has many causes. Likely causes of fever depend on whether it has lasted 7 days or less (acute) or more than 7 days (chronic), as well as on the age of the child.

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 are

  • Respiratory infections due to a virus, such as colds or flu

  • Gastroenteritis (infection of the digestive tract) due to a virus

  • 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 bodywide infection), pneumonia, and meningitis.

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—see Occult Bacteremia). 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, occult bacteremia is less common. However, pneumococcal strains that are not a part of the current pneumococcal vaccine or other bacteria can sometimes cause it.

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), and viral or bacterial infections of the brain (encephalitis), 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.


Chronic fever

Chronic fever most commonly results from

  • A prolonged viral illness

  • Back-to-back viral illnesses, especially in young children

Chronic fever can also be caused by many other infectious and noninfectious disorders. Infectious causes include hepatitis, sinusitis, pneumonia, pockets of pus (abscesses) in the abdomen, infections of the digestive tract caused by bacteria or parasites, bone infections (osteomyelitis), heart infections (endocarditis), and tuberculosis. Noninfectious causes include Kawasaki disease, inflammatory bowel disease, juvenile idiopathic arthritis or other connective tissue disorders, and cancer (such as leukemia and lymphoma). 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

  • Any fever in infants less than 2 months old

  • Lethargy or listlessness

  • Ill appearance

  • Difficulty breathing

  • Bleeding in the skin, appearing as tiny reddish purple dots (petechiae) or splotches (purpura)

  • Continuous crying in an infant or toddler (inconsolability)

  • 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 36 months old 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 36 months old, 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 36 months 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 Examination of the Febrile Child).

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.

Some Common Causes and Features of Fever in Children

Cause

Common Features*

Tests

Acute (lasting 7 days or less)

Respiratory infections due to a virus

A runny or congested nose

Usually a sore throat and cough

Sometimes swollen lymph nodes in the neck, without redness and tenderness

A doctor’s examination

Other infections due to a virus

In some infants or children, no symptoms except fever

A doctor's examination

Gastroenteritis

Diarrhea

Often vomiting

Possibly recent contact with infected people or certain animals or consumption of contaminated food or water

A doctor’s examination

Sometimes examination and testing of stool

Ear infection (otitis media)

Pain in one ear (difficult to detect in infants and young children who do not talk)

Sometimes rubbing or pulling at the ear

A doctor’s examination

Throat infections (pharyngitis)

A red, swollen throat

Pain when swallowing

A doctor’s examination

Sometimes a throat culture or rapid strep test (both done on a sample taken from the back of the throat with a swab)

Occult bacteremia

In children under 3 years old

No other symptoms

Blood tests

Pneumonia

Cough and rapid breathing

Often chest pain, shortness of breath, or both

A doctor's examination

Usually a chest x-ray

Skin infections (cellulitis)

A red, painful, slightly swollen area of skin

A doctor’s examination

Urinary tract infection

Pain during urination

Sometimes blood in urine

Sometimes back pain

In infants, vomiting and poor feeding

Urine tests

Encephalitis (a rare infection of the brain)

Infants: Sometimes bulging of the soft spots (fontanelles) between the skull bones, sluggishness (lethargy) or inconsolability

Older children: Headache, confusion, or lethargy

A spinal tap (lumbar puncture)

Meningitis (uncommon)

Newborns: Bulging of the soft spots (fontanelles) between the skull bones, inconsolability, poor feeding, and/or lethargy

Infants: Fussiness and irritability especially when held, inconsolability, poor feeding, and/or lethargy

Older children: Headache, sensitivity to light, lethargy, vomiting, and/or a stiff neck that makes lowering the chin to the chest difficult

A spinal tap

Vaccines

Recent vaccination

A doctor’s examination

Kawasaki disease

Fever for more than 5 days

Red eyes, lips, and tongue

Painful swelling of hands and feet

Often a rash

Sometimes swollen lymph nodes in the neck

A doctor's examination

Blood tests

ECG and echocardiography

Sometimes urine tests, ultrasonography of the abdomen, or an eye examination

Acute rheumatic fever

Swollen, painful joints

New heart murmur detected during a doctor's examination

Sometimes a rash or bumps under the skin

Sometimes jerky, uncontrollable movements or changes in behavior

Often a history of strep throat

Blood tests

A throat culture

ECG and echocardiography

Chronic (lasting more than 7 days)

Infections due to a virus, such as

  • Epstein-Barr virus

  • Cytomegalovirus

  • Hepatitis viruses

  • Arboviruses

Long-lasting weakness and tiredness

Sometimes swollen lymph nodes in the neck, a sore throat, or both

Sometimes yellow discoloration of the whites of the eyes (jaundice)

Blood tests

Sinusitis

Intermittent headaches, a runny nose, and congestion

CT of the sinuses

Abdominal abscess (a pocket of pus inside the abdomen)

Abdominal pain and often tenderness to the touch

CT of the abdomen

Joint infection (septic arthritis)

Swollen, red, painful joint

Testing of a sample of fluid taken from the joint with a needle

Bone infection (osteomyelitis)

Pain in affected bone

Sometimes a skin infection near the affected bone

Bone scan, MRI of bone, or both

Sometimes biopsy of bone to check for bacteria (culture)

Endocarditis

Sometimes a heart murmur

Blood tests for bacteria (blood culture)

Echocardiography

Tuberculosis (uncommon)

Poor weight gain or weight loss

Night sweats

Cough

Chest x-ray

Skin tests

Possibly culture of a sputum sample, and/or blood tests

Malaria (varies by geographic location)

A shaking chill followed by a fever that can exceed 104° F (40° C)

Fatigue and vague discomfort (malaise), headache, body aches, and nausea

Blood tests

Lyme disease

Sometimes headache and neck pain

Sometimes a swollen, painful joint (such as the knee)

Sometimes a bull’s-eye rash in one or more locations

Occasionally a known history of a tick bite

A doctor's examination

Sometimes blood tests

Cat-scratch disease

Often a swollen, painful lymph node

Sometimes a bump on the skin where scratched by a cat

Blood tests

Inflammatory bowel disease

  • Crohn disease

  • Ulcerative colitis

Blood in stool, crampy abdominal pain, weight loss, and loss of appetite

Sometimes arthritis, rashes, sores in the mouth, and tears in the rectum

Colonoscopy

Sometimes CT or x-rays after barium is inserted in the rectum (barium enema)

Joint and connective tissue disorders, such as

  • Juvenile idiopathic arthritis

  • Systemic lupus erythematosus (lupus)

Swollen, red, tender joints

Often a rash

Sometimes fatigue

Blood tests

Cancer, such as

  • Leukemia

  • Lymphoma

  • Neuroblastoma

  • Bone tumors

Poor weight gain or weight loss and loss of appetite

Night sweats

Possibly bone pain

A complete blood cell count

Removal (aspiration) of a sample of bone marrow for examination

Sometimes a bone scan, and/or MRI of bone

Sometimes CT of the chest or abdomen

Periodic fever syndromes, such as

  • Periodic fever with aphthous stomatitis, pharyngitis, and adenitis (PFAPA)

  • Familial Mediterranean fever

  • Cyclic neutropenia

Fever that recurs in often predictable cycles with periods of wellness in between

Sometimes mouth sores, sore throat, and swollen lymph nodes

Sometimes chest or abdominal pain

Sometimes family members who have had similar symptoms or have been diagnosed with one of the familial periodic fever syndromes

A doctor's examination during episodes of fever

Blood tests during and between fever episodes

Sometimes genetic testing

Pseudo fever of unknown origin

Usually a misinterpretation of normal fluctuations in body temperature or overinterpretation of frequent, minor viral illnesses

Usually no other symptoms of concern

Normal examination findings

A doctor's examination

Thorough and accurate recording of illnesses and temperatures as well as a description of the overall function of the child and family

Occasionally blood tests to rule out other causes and reassure parents

*Features include symptoms and results of the doctor's examination. Features mentioned are typical but not always present. Disorders that cause chronic fever also cause fever during the first 7 to 10 days.

CT = computed tomography; ECG = electrocardiogram; MRI = magnetic resonance imaging.


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 Examination of the Febrile Child).

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—see Tests for Brain, Spinal Cord, and Nerve Disorders : Spinal Tap), 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 occult 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 aged 3 to 36 months 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 36 months old, 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 (see Biology of Infectious Disease:Testing). 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 treatment focuses on making children feel better.

General measures

Ways to help children with a fever feel better without using drugs include

  • Giving children plenty of fluids to prevent dehydration

  • Putting cool, wet cloths (compresses) on their forehead, wrists, and calves

  • 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:

  • Acetaminophen, given by mouth or by suppository

  • Ibuprofen, given by mouth

Acetaminophen tends to be preferred. However, some doctors are concerned that acetaminophen use has contributed to the recent increase in asthma in children and thus do not recommend its use in children with asthma or who have a family history of asthma. 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 (see Reye Syndrome).


Key Points

  • Usually, fever is caused by a viral infection.

  • The likely causes of fever and need for testing depend on the age of the child.

  • Infants under 2 months of age with a temperature of 100.4° F or higher need to be evaluated by a doctor.

  • Children aged 3 to 36 months 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.

  • Teething does not cause significant fever.

  • Drugs that lower fever may make children feel better but do not affect the disorder causing the fever.

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