Normal body temperature varies from person to person and throughout the day. Normal body temperature is highest in children who are preschool aged. Several studies have documented that peak temperature tends to be in the afternoon and is highest at about 18 to 24 months of age when many normal healthy children have a temperature as high as 38.3° C (101° F). However, fever usually is defined as a core body (rectal) temperature ≥ 38.0° C (100.4° F).
Significance of fever depends on clinical context rather than peak temperature; some minor illnesses cause high fever, whereas some serious illnesses cause only a mild temperature elevation. Although parental assessment is frequently clouded by fear of fever, the history of a temperature taken at home should be considered equivalent to a temperature taken in the office.
(See also Fever in Adults.)
Pathophysiology of Fever in Infants and Children
Fever occurs in response to the release of endogenous pyrogenic mediators called cytokines (in particular interleukin-1 [IL-1]). Cytokines stimulate the production of prostaglandins by the hypothalamus; prostaglandins readjust and elevate the temperature set point.
Fever plays an integral role in fighting infection and, although it may be uncomfortable, does not necessitate treatment in an otherwise healthy child. Some studies even indicate that lowering the temperature can prolong some illnesses. However, fever increases the metabolic rate and the demands on the cardiopulmonary system. Therefore, fever can be detrimental to children with pulmonary or cardiac compromise or neurologic impairment. It can also be the catalyst for febrile seizures, which although typically benign, are very concerning to parents and must also be distinguished from more serious disorders (eg, meningitis).
Etiology of Fever in Infants and Children
Causes of fever ( see Table: Some Common Causes of Fever in Children) differ based on whether the fever is acute (≤ 14 days ), acute recurrent or periodic (episodic fever separated by afebrile periods), or chronic (> 14 days), which is more commonly referred to as fever of unknown origin (FUO). Response to antipyretics and height of the temperature have no direct relationship to the etiology.
Acute fever
Most acute fevers in infants and young children are caused by infection. The most common are
Viral respiratory or gastrointestinal infections (most common causes overall)
Certain bacterial infections (otitis media, pneumonia, urinary tract infections)
However, potential infectious causes of acute fever vary with the child’s age. Neonates (infants < 28 days) are considered functionally immunocompromised because they often fail to contain infection locally and, as a result, are at higher risk of serious invasive bacterial infections most commonly caused by organisms acquired during the perinatal period. The most common perinatal pathogens in neonates are group B streptococci, Escherichia coli (and other gram-negative enteric organisms), Listeria monocytogenes, and herpes simplex virus. These organisms can cause bacteremia (viremia with herpes simplex), pneumonia, pyelonephritis, meningitis, and/or sepsis.
Most febrile children 1 month to 2 years of age without an obvious focus of infection on examination (fever without source [FWS]) have self-limited viral disease. However, a small number (perhaps < 1% in the postconjugate vaccine era) of such patients are early in the course of a serious infection (eg, bacterial meningitis). Thus, the main concern in a patient with FWS is whether occult bacteremia (pathogenic bacteria in the bloodstream without focal symptoms or signs on examination) is present. The most common causative organisms of occult bacteremia are Streptococcus pneumoniae and Haemophilus influenzae type b. The widespread use of vaccinations against both of these organisms has made occult bacteremia much less common.
Noninfectious causes of acute fevers include Kawasaki disease, heatstroke, and toxic ingestions (eg, of drugs with anticholinergic effects). Some vaccinations can cause fever either in the first 24 to 48 hours after the vaccine is given (eg, with pertussis vaccination) or 1 to 2 weeks after the vaccine is given (eg, with measles vaccination). These fevers typically last from a few hours to a day. If the child is otherwise well, no evaluation is necessary. Teething does not cause significant or prolonged fevers.
Acute recurrent or periodic fever
Acute recurrent or periodic fever is episodes of fever alternating with periods of normal temperature ( see Table: Some Common Causes of Fever in Children).
Chronic fever
Fever that occurs daily for ≥ 2 weeks and for which initial cultures and other investigations fail to yield a diagnosis is considered fever of unknown origin (FUO).
Potential categories of causes ( see Table: Some Common Causes of Fever in Children) include localized or generalized infection, connective tissue disease, and cancer. Miscellaneous specific causes include inflammatory bowel disease, diabetes insipidus with dehydration, and disordered thermoregulation. Pseudo FUO is likely much more common than true FUO because frequent, minor viral illness may be overinterpreted. In children, despite the numerous possible causes, true FUO is more likely to be an uncommon manifestation of a common disease rather than an uncommon disease; respiratory infections account for almost one half of cases of infection-associated FUO.
Evaluation of Fever in Infants and Children
History
History of present illness should note degree and duration of fever, method of measurement, and the dose and frequency of antipyretics (if any). Important associated symptoms that suggest serious illness include poor appetite, irritability, lethargy, and change in crying (eg, duration, character). Associated symptoms that may suggest the cause include vomiting, diarrhea (including presence of blood or mucus), cough, difficulty breathing, favoring of an extremity or joint, and strong or foul-smelling urine. Drug history should be reviewed for indications of drug-induced fever.
Factors that predispose to infection are identified. In neonates, these factors include prematurity, prolonged rupture of membranes, maternal fever, and positive prenatal tests (usually for group B streptococcal infections, cytomegalovirus infections, or sexually transmitted diseases). For all children, predisposing factors include recent exposures to infection (including family, caregiver, and school or daycare infection), indwelling medical devices (eg, catheters, ventriculoperitoneal shunts), recent surgery, travel and environmental exposures (eg, to endemic areas, to ticks, mosquitoes, cats, farm animals, or reptiles), and known or suspected immune deficiencies.
Review of systems should note symptoms suggesting possible causes, including runny nose and congestion (viral upper respiratory infection), headache (sinusitis, Lyme disease, meningitis), ear pain or waking in the night with signs of discomfort (otitis media), cough or wheezing (pneumonia, bronchiolitis), abdominal pain (pneumonia, strep pharyngitis, gastroenteritis, urinary tract infection, abdominal abscess), back pain (pyelonephritis), and any history of joint swelling or redness (Lyme disease, osteomyelitis). A history of repeated infections (immunodeficiency) or symptoms that suggest a chronic illness, such as poor weight gain or weight loss (tuberculosis, cancer), is identified. Certain symptoms can help direct the evaluation toward noninfectious causes; they include heart palpitations, sweating, and heat intolerance (hyperthyroidism) and recurrent or cyclic symptoms (a rheumatoid, inflammatory, or hereditary disorder).
Past medical history should note previous fevers or infections and known conditions predisposing to infection (eg, congenital heart disease, sickle cell anemia, cancer, immunodeficiency). A family history of an autoimmune disorder or other hereditary conditions (eg, familial dysautonomia, familial Mediterranean fever) is sought. Vaccination history is reviewed to identify patients at risk of infections that can be prevented by a vaccine.
Physical examination
Vital signs are reviewed, noting abnormalities in temperature and respiratory rate. In ill-appearing children, blood pressure should also be measured. Temperature should be measured rectally in infants for accuracy. Any child with cough, tachypnea, or labored breathing requires pulse oximetry.
The child’s overall appearance and response to the examination are important. A febrile child who is overly compliant or listless is of more concern than one who is uncooperative. However, an irritable infant or child who is inconsolable is also of concern. The febrile child who looks quite ill, especially when the temperature has come down, is of great concern and requires in-depth evaluation and continued observation. However, children who appear more comfortable after antipyretic therapy do not always have a benign disorder.
The remainder of the physical examination seeks signs of causative disorders ( see Table: Examination of the Febrile Child).
Red flags
The following findings are of particular concern:
Age < 1 month
Lethargy, listlessness, or toxic appearance
Respiratory distress
Petechiae or purpura
Inconsolability
Interpretation of findings
Although serious illness does not always cause high fever and many high fevers result from self-limited viral infections, a temperature of ≥ 39° C in children < 36 months indicates higher risk of serious bacterial infection.
Other vital signs also are significant. Hypotension should raise concern about hypovolemia, sepsis, or myocardial dysfunction. Tachycardia in the absence of hypotension may be caused by fever (10 to 20 beats/minute increase for each degree above normal) or hypovolemia. An increased respiratory rate may be a response to fever, indicate a pulmonary source of the illness, or be respiratory compensation for metabolic acidosis.
Acute fever is infectious in most cases, and, of these, most are viral. History and examination are adequate to make a diagnosis in children > 36 months who are otherwise well and not toxic-appearing. Typically, they have a viral respiratory illness (recent ill contact, runny nose, wheeze, or cough) or gastrointestinal illness (ill contact, diarrhea, and vomiting). Other findings also suggest specific causes ( see Table: Examination of the Febrile Child).
In infants and children < 36 months, the possibility of occult bacteremia, plus the frequent absence of focal findings in neonates and young infants with serious bacterial infection, necessitates a different approach. Evaluation varies by age group. Accepted categories are neonates (≤ 28 days), young infants (1 to 3 months), and older infants and children (3 to 36 months). Regardless of clinical findings, a neonate with fever requires immediate hospitalization and testing to rule out a dangerous infection. Young infants may require hospitalization depending on screening laboratory results and the likelihood that they will be brought in for follow-up.
Acute recurrent or periodic fever and chronic fever (FUO) require a high index of suspicion for the many potential causes. However, certain findings can suggest the disorder: aphthous stomatitis, pharyngitis and adenitis (PFAPA syndrome); intermittent headaches with runny nose or congestion (sinusitis); weight loss, high-risk exposure, and night sweats (tuberculosis); weight loss or difficulty gaining weight, heart palpitations, and sweating (hyperthyroidism); and weight loss, anorexia, and night sweats (cancer).
Testing
Testing for Acute Fever
For acute fever, testing for infectious causes is directed by the age of the child. Typically, children < 36 months, even those who do not appear very ill and those who have an apparent source of infection (eg, otitis media), require a thorough search to rule out serious bacterial infections (eg, meningitis, sepsis/bacteremia, urinary tract infection). In this age group, early follow-up (by phone and/or outpatient visit) is important for all those managed at home.
Febrile children < 1 month of age
All febrile children < 1 month of age require a white blood cell (WBC) count with a manual differential, blood cultures, urinalysis and urine culture (obtained by catheterization, not an external bag), and cerebrospinal fluid (CSF) evaluation with culture and appropriate polymerase chain reaction (PCR) testing (eg, for herpes simplex, enterovirus) as indicated by historical risk factors. Inflammatory marker levels (C-reactive protein, procalcitonin, or both) may be measured to assist with risk assessment. Chest x-ray is done in neonates with respiratory manifestations. Stool is sent for culture or enteric PCR stool test in neonates with diarrhea.
acyclovir is stopped if CSF HSV PCR testing and mucocutaneous vesicle HSV culture (if done) results are negative.
Febrile children between 1 month and 3 months of age
Febrile children between 1 month and 3 months of age require a different approach, which has evolved over the last few decades because the number of children in this age group who turn out to have a potentially serious bacterial infection has been markedly reduced by routine immunization against H. influenzae type b and S. pneumoniae. Clinicians must nonetheless maintain vigilance because, although serious bacterial infections have been reduced, they have not been eliminated. Therefore, clinicians who choose to observe without treatment or send home under parental observation need to have a greater certainty regarding that child's low-risk status than that of a child who is tested, admitted, and treated.
Infants in this 1- to 3-month age group are differentiated based on
Temperature
Clinical appearance (ill- or well-appearing, as below)
Laboratory results
Ill-appearing febrile infants
Well-appearing febrile infants
Well-appearing febrile infants between 29 days and 60 days of age with all of the following are at low risk of serious bacterial infections:
Rectal temperature ≤ 38.5° C
Normal WBC count (5,000 to 15,000/mcL [5 to 15 × 109/L] and an absolute neutrophil count ≤ 4000/mcL [≤ 4 × 109/L])
Normal inflammatory marker levels (procalcitonin ≤ 0.5 ng/mL [≤ 0.5 mcg/L] and/or CRP ≤ 2 mg/dL [≤ 20 mg/L])
Normal urinalysis (and CSF analysis and chest x-ray, if done)
Blood and urine cultures should be obtained. Some experts defer lumbar puncture in these infants who meet the above criteria, but guidelines regarding minimum necessary testing in this age group continue to evolve based on changing bacteriology and advances in testing (eg, inflammatory markers, pathogen identification with rapid PCR testing) (1).
In addition, well-appearing febrile infants in this age group with a respiratory syncytial virus (RSV), influenza, or other viral infection documented by PCR testing during a period of high seasonal prevalence and who have a normal urinalysis seem to have a markedly reduced risk of serious bacterial infection, which some experts believe permits modifications to the above recommendations, meaning the infants might not necessarily require blood or CSF studies.
In well-appearing febrile infants between 61 days and 90 days of age without risk factors for serious bacterial infection, many experts defer blood and CSF studies pending urinalysis results.
When testing is done in well-appearing infants between 1 month and 3 months of age, infants who have any of the following should be admitted to the hospital for treatment with age-specific empiric parenteral antibiotics as described above:
CSF pleocytosis
An abnormal urinalysis or chest x-ray
A peripheral WBC count ≤ 5,000/mcL (≤ 5 × 109/L) or ≥ 15,000/mcL (≥ 15 × 109/L)
An absolute neutrophil count > 4000/mcL (> 4 × 109/L)
Abnormal inflammatory marker levels (procalcitonin > 0.5 ng/mL [> 0.5 mcg/L] and/or CRP > 2 mg/dL [> 20 mg/L])
If empiric antibiotics are to be given, lumbar puncture with CSF analysis should be strongly considered if not previously done, especially in infants 29 to 60 days of age.
Some experts believe that well-appearing infants between 1 month and 3 months of age with an abnormal urinalysis but otherwise reassuring examination and laboratory results can be safely managed with antibiotics at home if close follow-up is assured within 24 hours (1).
Febrile children between 3 months and 36 months of age
Febrile children between 3 months and 36 months of age who have an apparent source of fever on examination and who do not appear ill or toxic can be managed based on the clinical diagnosis. Children in this age group who are ill-appearing should be fully evaluated for serious bacterial infection with WBC count and cultures of blood, urine, and, when meningitis is suspected, CSF. Those with tachypnea or a WBC count > 20,000/mcL (> 20 × 109S. pneumoniae, Staphylococcus aureus, Neisseria meningitidis, H. influenzae type b) and be admitted to the hospital pending culture results.
Well-appearing children in this age group who have a temperature > 39° C and no identifiable source on examination (fever without source) and who are not fully immunized have a risk of occult bacteremia as high as 5% (equal to the risk before the pneumococcal and H. influenzae conjugate vaccines came into use). These children should have a complete blood count with differential, blood culture, and urinalysis and urine culture. A chest x-ray should be done if the WBC count is ≥ 20,000/mcL (≥ 20 × 109/L) . Children who have a WBC count ≥ 15,000/mcL (≥ 15 × 109≥ 38° C) after 48 hours or earlier if they become sicker or if new symptoms or signs develop.
Well-appearing children in this age group who have a temperature > 39° C and fever without identifiable source and who are completely immunized have a risk of bacteremia < 0.5%. At this low-risk level, most laboratory testing and empiric antibiotic therapy are neither indicated nor cost-effective. However, because urinary tract infection (UTI) can be an occult source of infection in fully immunized children in this age group, girls < 24 months, circumcised boys < 6 months, and uncircumcised boys < 12 months should have a urinalysis and urine culture (obtained by catheterization, not an external bag) and be appropriately treated if UTI is detected. For other completely immunized children, urine testing is done only when they have symptoms or signs of UTI, they have a prior history of UTI or urogenital anomalies, or fever has lasted > 48 hours.
For all children, caregivers are instructed to return immediately if fever becomes higher, the child looks sicker, or new symptoms or signs develop.
Febrile children > 36 months of age
For febrile children > 36 months of age, testing is directed by history and examination. In this age group, a child's response to serious illnesses is sufficiently developed to be recognized clinically (eg, nuchal rigidity is a reliable finding of meningeal irritation), so empiric testing (eg, screening WBC counts, urine and blood cultures) is not indicated.
Acute recurrent or periodic fever
For acute recurrent or periodic fever, laboratory tests and imaging should be directed toward likely causes based on findings from the history and physical examination. PFAPA syndrome should be considered in young children who have periodic high fever at intervals of about 3 to 5 weeks with aphthous ulcers, pharyngitis, and/or adenitis. Between episodes and even during the episodes, the children appear healthy. Diagnosis requires 6 months of stereotypic episodes, negative throat cultures during episodes, and exclusion of other causes (eg, specific viral infections). In patients with attacks of fever, arthralgia, skin lesions, mouth ulcers, and diarrhea, IgD levels should be measured to look for hyperimmunoglobulinemia D syndrome (HIDS). Laboratory features of HIDS include elevated C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) and markedly elevated IgD (and often IgA).
Genetic testing is available for familial Mediterranean fever (FMF), TNF receptor–associated periodic syndrome (TRAPS), and HIDS.
Testing for acute fever reference
1. Pantell RH, Roberts KB, Adams WG, et al: Evaluation and management of well-appearing febrile infants 8 to 60 days old. Pediatrics 148(2):e2021052228, 2021. doi: 10.1542/peds.2021-052228
Testing for Chronic Fever
For chronic fever (fever of unknown origin [FUO]), laboratory tests and imaging should be directed toward likely causes of fever based on the patient's age and findings from the history and physical examination. Indiscriminate ordering of laboratory tests is unlikely to be helpful and can be harmful (ie, because of adverse effects of unnecessary confirmatory testing of false positives). The pace of the evaluation is dictated by the appearance of the child. The pace should be rapid if the child is ill-appearing, but can be more deliberate if the child appears well.
All children with FUO should have
Complete blood count with manual differential
Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
Blood cultures
Urinalysis and urine culture
Chest x-ray
HIV serology
Tuberculin skin test or interferon-gamma release assay
The results of these studies in conjunction with findings from the history and physical examination can focus further diagnostic tests.
Anemia may be a clue to malaria, infective endocarditis, inflammatory bowel disease, systemic lupus erythematosus, or tuberculosis (TB). Thrombocytosis is a nonspecific acute-phase reactant. The total WBC count and the differential generally are less helpful, although children with an absolute neutrophil count > 10,000/mcL (> 10 × 109/L) have a higher risk of serious bacterial infection. If atypical lymphocytes are present, a viral infection is likely. Immature WBCs should prompt further evaluation for leukemia. Eosinophilia may be a clue to parasitic, fungal, neoplastic, allergic, or immunodeficiency disorders.
The ESR and CRP are nonspecific acute-phase reactants that are general indicators of inflammation; an elevated ESR or CRP makes factitious fever less likely. A normal ESR or CRP can slow the pace of the evaluation. However, ESR or CRP may be normal in noninflammatory causes of FUO ( see Table: Some Causes of Fever of Unknown Origin (FUO)).
Blood cultures should be done in all patients with FUO at least once and more often if suspicion of serious bacterial infection is high. Three blood cultures should be done over 24 hours in patients who have any manifestations of infective endocarditis. A positive blood culture, particularly for S. aureus, should raise suspicion for occult skeletal or visceral infection or endocarditis and lead to performance of a bone scan and/or echocardiography.
Urinalysis and urine culture are important because UTI is among the most frequent causes of FUO in children. Patients with FUO should have a chest x-ray to check for infiltrates and lymphadenopathy even if lung examination is normal. Serum electrolytes, BUN, creatinine, and hepatic enzymes are measured to check for renal or hepatic involvement. HIV serologic tests and a tuberculin skin test (using purified protein derivative) or interferon-gamma release assay are done because primary HIV infection or TB can manifest as FUO.
Other tests are done selectively based on findings:
Stool testing
Bone marrow examination
Serologic testing for specific infections
Testing for connective tissue and immunodeficiency disorders
Imaging
Stool cultures or examination for ova and parasites may be warranted in patients with loose stools or recent travel. Salmonella enteritis can infrequently manifest as FUO without diarrhea.
Bone marrow examination in children is most useful in diagnosing cancer (especially leukemia) or other hematologic disorders (eg, hemophagocytic disease) and may be warranted in children with otherwise unexplained hepatosplenomegaly, lymphadenopathy, or cytopenias.
Serologic testing that may be warranted, depending on the case, includes but is not limited to Epstein-Barr virus infection, cytomegalovirus infection, toxoplasmosis, bartonellosis (cat-scratch disease), syphilis, and certain fungal or parasitic infections.
An antinuclear antibody (ANA) test should be done in children > 5 years with a strong family history of rheumatologic disease. A positive ANA test suggests an underlying connective tissue disorder, particularly systemic lupus erythematosus. Immunoglobulin levels (IgG, IgA, and IgM) should be measured in children with a negative initial evaluation. Low levels may indicate an immunodeficiency. Elevated levels can occur in chronic infection or an autoimmune disorder.
Imaging of the nasal sinuses, mastoids, and gastrointestinal tract should be done initially only when children have symptoms or signs related to those areas but may be warranted in children in whom FUO remains undiagnosed after initial testing. Children with elevated ESR or CRP, anorexia, and weight loss should have studies to exclude inflammatory bowel disease, particularly if they also have abdominal complaints with or without anemia. However, imaging of the gastrointestinal tract should be done eventually in children whose fevers persist without other explanation and may be caused by disorders such as psoas abscess or cat-scratch disease. Ultrasonography, CT, and MRI can be useful in evaluating the abdomen and can detect abscesses, tumors, and lymphadenopathy.
Imaging of the central nervous system is generally not helpful in the evaluation of children with FUO. However, lumbar puncture may be warranted in children with persistent headache, neurologic signs, or an indwelling ventriculoperitoneal shunt.
Other imaging techniques, including bone scan or tagged WBC scan, can be helpful in selected children whose fevers persist without other explanation when suspicion for a source that could be detected by these tests exists.
Ophthalmologic examination by slit lamp is useful in some patients with FUO to look for uveitis (eg, as occurs in juvenile idiopathic arthritis) or leukemic infiltration.
Biopsy (eg, of lymph nodes or liver) should be reserved for children with evidence of involvement of specific organs.
Empiric treatment with anti-inflammatory drugs or antibiotics should not be used as a diagnostic measure except when juvenile idiopathic arthritis is suspected; in such cases, a trial of nonsteroidal anti-inflammatory drug (NSAIDs) is the recommended first-line therapy. Response to anti-inflammatory drugs or antibiotics does not help distinguish infectious from noninfectious causes. Also, antibiotics can cause false-negative cultures and mask or delay the diagnosis of important infections (eg, meningitis, parameningeal infection, endocarditis, osteomyelitis).
Treatment of Fever in Infants and Children
Treatment is directed at the underlying disorder.
Fever in an otherwise healthy child does not necessarily require treatment. Although antipyretics can provide comfort, they do not change the course of an infection. In fact, fever is an integral part of the inflammatory response to infection and can help the child fight the infection. However, most clinicians use antipyretics to help alleviate discomfort and to reduce physiologic stresses in children who have cardiopulmonary disorders, neurologic disorders, or a history of febrile seizures.
Antipyretic drugs that are typically used include
1Reye syndrome if certain viral illnesses such as influenza and varicella are present.
Nondrug approaches to fever include putting the child in a warm or tepid bath, using cool compresses, and undressing the child. Caregivers should be cautioned not to use a cold water bath, which is uncomfortable and which, by inducing shivering, may paradoxically elevate body temperature. As long as the temperature of the water is slightly cooler than the temperature of the child, a bath provides temporary relief.
Things to avoid
Wiping the body down with isopropyl alcohol should be strongly discouraged because alcohol can be absorbed through the skin and cause toxicity. Numerous folk remedies exist, ranging from the harmless (eg, putting onions or potatoes in socks) to the uncomfortable (eg, coining, cupping).
Treatment reference
1. Sheehan WJ, Mauger DT, Paul IM, et alN Engl J Med 375(7):619–630, 2016. doi: 10.1056/NEJMoa1515990
Key Points
Most acute fever is caused by viral infections.
Causes and evaluation of acute fever differ depending on the age of the child; in young infants, fever may indicate a serious, life-threatening disease and requires careful evaluation.
A small but real number of children < 36 months of age with fever without localizing signs (primarily those who are incompletely immunized) can have pathogenic bacteria in their bloodstream (occult bacteremia) and be early in the course of a potentially life-threatening infection.
Teething does not cause significant fever.
Antipyretics do not alter the outcome but may make children feel better.
