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Literature review current through: Oct 2014. | This topic last updated: Sep 05, 2014.

INTRODUCTION — Fever is a common symptom among children seeking medical care. Most children undergo evaluation for a febrile illness before their third birthday, and nearly one-third of pediatric outpatient visits are for fever [1-3].

When the history and physical examination cannot identify a specific source of fever in an acutely ill, nontoxic-appearing child less than three years of age, the illness is often called fever without a source (FWS). Alternative terms are fever without localizing signs (FWLS) or fever without a focus.

This topic will review the etiology, evaluation, and management of the child 3 to 36 months of age with fever of less than seven days duration. Fever in newborns, infants younger than three months, and fever of unknown origin (≥7 days) are reviewed separately. (See "Evaluation and management of fever in the neonate and young infant (younger than three months of age)" and "Fever of unknown origin in children: Evaluation" and "Etiologies of fever of unknown origin in children".)

BACKGROUND

Fever of concern — In children 3 to 36 months of age, the diagnosis of fever is based upon core temperature, which is measured most accurately rectally. The history of an elevated temperature recorded at home should be considered equivalent to that taken in a medical facility. Fever 39ºC (102.2ºF) or higher is the threshold above which evaluation for a source of occult infection, including urinary tract infection (UTI), may be warranted [4]. (See 'Occult sources of infection' below.)

The majority of children with fever have either a self-limited viral infection or a recognizable source of bacterial infection. However, research in the 1970s identified a population of well-appearing febrile young children who had occult bacteremia [5,6]. Subsequent studies demonstrated that some of these children went on to develop serious focal bacterial infections, such as pneumonia and meningitis [7,8]. Although laboratory testing identified a group of children at an increased risk for occult bacteremia, many who were not bacteremic received presumptive treatment with broad spectrum antibiotics while awaiting definitive blood culture results.

The introduction of vaccines to prevent Haemophilus influenzae type b (Hib) and pneumococcal disease has dramatically lowered the incidence of occult bacteremia and, as a result, changed the issues facing the clinician who is evaluating a young child with fever. (See 'Impact of vaccines' below.)

Population of interest — This topic will focus on the evaluation and management of well-appearing, immunocompetent children 3 to 36 months of age with fever ≥39ºC (102.2ºF) of less than seven days duration and no focus of infection identified by a complete physical examination. The evaluation of the febrile infant younger than three months is discussed separately. (See "Evaluation and management of fever in the neonate and young infant (younger than three months of age)".)

Immunization status — The approach to the child who has fever without a source is greatly determined by immunization status.

Complete immunization — In the discussion that follows, a completely immunized child has received the primary booster series of three immunizations with conjugate vaccines Streptococcus pneumoniae (PCV7 or PCV13), at least two doses of Haemophilus influenzae, type b (Hib), and remains on schedule. However, some experts consider two doses of PCV7 or PCV13 sufficient to prevent invasive Streptococcus pneumoniae infection. Patients who have not received the booster 12 to 15 months after the third Hib and either PCV7 or PCV13 are also considered to be at much lower risk of bacteremia. (See "Pneumococcal (Streptococcus pneumoniae) conjugate vaccines in children", section on 'Alternative or abbreviated schedule'.)

Incomplete immunization — In the discussion that follows, an incompletely immunized child has not received the primary booster series of three vaccinations with both Hib and either PCV7 or PCV13. Based on these criteria, any child under six months of age is incompletely immunized.

CAUSES OF FEVER — Fever can be caused by infectious and noninfectious processes. The vast majority of young children with fever have an infectious etiology. Noninfectious etiologies include drug fever, immunization reactions, central nervous system dysfunction, malignancy (eg, leukemia), and chronic inflammatory conditions (ie, inflammatory bowel disease and juvenile idiopathic arthritis).

Although caretakers may sometimes attribute fever to teething, fever >38.5ºC is unlikely to be caused by teething [9]. (See "Anatomy and development of the teeth", section on 'Primary teeth eruption'.)

The source of fever may be a recognizable bacterial or viral illness. In a study of a large cohort of children 3 to 36 months of age presenting to a primary care provider with a febrile illness, a readily identifiable presumed bacterial illness was diagnosed at the initial encounter in 56 percent of children, almost 90 percent of whom had otitis media [1]. A specific viral infection (eg, croup, bronchiolitis, varicella, roseola) was identified in an additional 4 percent of children [1]. Similarly, 6 percent of 21,216 children 3 to 36 months of age with fever ≥39ºC seen in the emergency department of an urban tertiary care children's hospital had a recognizable viral syndrome, 47 percent had fever without a source (FWS), and 47 percent had a specific bacterial infection requiring antibiotics or chronic illness (eg, immunocompromised state, central line) that affected the fever evaluation [10].

Serious bacterial infectious syndromes that occur in children 3 to 36 months of age include meningitis, pneumonia, and cellulitis. In one series (prior to the introduction of Hib and pneumococcal conjugate vaccines) of 996 febrile children less than 36 months of age, <1 percent had meningitis, 10 percent had focal soft tissue infections, and 30 percent had pneumonia [11]. These diagnoses are discussed in detail elsewhere. (See "Bacterial meningitis in children older than one month: Clinical features and diagnosis" and "Cellulitis and erysipelas" and "Community-acquired pneumonia in children: Clinical features and diagnosis", section on 'Clinical presentation'.)

OCCULT SOURCES OF INFECTION — The goal of the evaluation of a young child with fever is to identify sources of infection that require further evaluation and definitive treatment. Such infections are usually bacterial, although the majority of children who are well-appearing and have no identifiable source of infection have a nonspecific self-limited viral illness [1,12]. The remainder of this discussion will focus on occult bacterial infections.

Pneumonia — Most children with fever and pneumonia have some abnormality on physical examination: usually tachypnea, abnormal auscultation, low pulse oximetry, retractions, or nasal flaring, suggesting respiratory tract disease [13-16]. However, a reliable physical examination in a young child can be a challenge. In an observational study, radiographic pneumonia was found in 20 to 30 percent of highly febrile young children (<5 years) without clinical evidence of pneumonia, but with a white blood cell count (WBC) ≥20,000/mm3 [17]. Similarly, another observational study demonstrated that 41 percent of children between 3 and 36 months of age with a WBC >25,000/mm3 had lobar or segmental pneumonia on chest radiograph [18]. This association between leukocytosis and pneumonia remains strong, even in the post-conjugate pneumococcal vaccine era [19]. (See "Community-acquired pneumonia in children: Clinical features and diagnosis", section on 'Clinical presentation'.)

Urinary tract infection — The urinary tract is the most common site of bacterial infection among febrile infants and young children. This finding was demonstrated in two large prospective studies [20,21]. The prevalence of urinary tract infection (UTI) in these reports was significantly influenced by demographic factors, such as sex, age, race, and circumcision status (table 1). (See "Urinary tract infections in children: Epidemiology and risk factors", section on 'Host factors'.)

The prevalence of UTI is highest among girls and warrants urinalysis and urine culture in all females age 3 to 24 months with fever ≥39ºC (102.2ºF) and no source (table 1).

Among boys, UTI is increased in uncircumcised compared with circumcised male infants with fever, with the greatest incidence in infants younger than three months of age (table 1). The low incidence of UTI among circumcised boys supports the practice of not routinely obtaining a catheterized urine specimen for culture in febrile, circumcised boys over six months of age.

Among highly febrile boys (ie, temperature ≥39ºC or 102.2ºF) who are 3 to 24 months with no source of infection, the probability of UTI is 10 to 25 percent in uncircumcised and 2 to 4 percent in circumcised [21]. The highest prevalence is found in younger boys. Furthermore, bladder catheterization is a painful, invasive procedure that many parents might prefer to avoid if their child's probability of disease is less than 5 percent. Thus, our practice is to evaluate for UTI in uncircumcised males ≤12 months and circumcised males ≤6 months. Some investigators suggest that high fever (ie, ≥39ºC or 102.2ºF) without a source is sufficient justification for urine studies on the first visit in all highly febrile boys between the age of 3 and 24 months [22]. (See 'Initial approach' below and "Urinary tract infections in children: Epidemiology and risk factors".)

Bacteremia — Bacteremia that occurs in a seriously ill patient with a focal infection, such as meningitis, septic arthritis, or cellulitis, is usually readily identified. The risk of sepsis in a child who is ill-appearing, febrile, and without an obvious source of infection is also apparent. This discussion will focus on the young febrile child who looks well and may have unsuspected, or occult, bacteremia.

Before routine immunization with Hib and either PCV7 or PCV13, the prevalence of occult bacteremia was 5 percent in well-appearing febrile children [5,6]. The predominant pathogens were S. pneumoniae (80 percent) and Hib (20 percent). Neisseria meningitidis represented a small number of cases.

Predictors — Factors associated with an increased the risk of occult bacteremia in unimmunized children to over 10 percent included [23-25]:

Age 3 to 36 months

Fever ≥39ºC

WBC ≥15,000/microL

Neither response to antipyretics nor clinical appearance predicted bacteremia [26-28].

Some children with bacteremia went on to have serious bacterial infections (SBI), including meningitis [7,29]. When children at risk for bacteremia were treated empirically with antibiotics until the results of blood cultures were known, they were less likely to develop these complications [23,24,30].

Impact of vaccines — The initiation of routine immunization of infants with the conjugate vaccines for Hib and S. pneumoniae has dramatically altered the prevalence of invasive disease due to these organisms. The incidence of occult bacteremia in well-appearing febrile children has fallen from 5 to below 1 percent, while the rate of isolation of a contaminant from blood cultures has remained constant at 1.8 to 3.0 percent [15,31-38]. (See "Pneumococcal (Streptococcus pneumoniae) conjugate vaccines in children", section on 'Invasive disease' and "Prevention of Haemophilus influenzae infection", section on 'Efficacy/effectiveness'.)

Since the routine immunization of children with PCV7 or PCV13 vaccine, pathogens other than S. pneumoniae are the cause of the majority of cases of unsuspected bacteremia [33]. E. coli and Staphylococcus aureus are frequently isolated organisms. Most reports of occult bacteremia also include cases caused by N. meningitidis, Group A streptococcus, and Salmonella species [33,39]. Laboratory parameters (ie, WBC >15,000/microL) may be less reliable predictors of bacteremia with these pathogens. (See 'WBC and ANC counts' below.)

In addition, the impact of PCV7 or PCV13 on variables, such as the role of nonvaccine serotypes in invasive pneumococcal disease and the duration and durability of protection after vaccination, continues to evolve. (See "Pneumococcal (Streptococcus pneumoniae) conjugate vaccines in children", section on 'Invasive disease' and "Impact of universal infant immunization with pneumococcal (Streptococcus pneumoniae) conjugate vaccines in the United States", section on 'Invasive disease caused by nonvaccine serotypes'.)

Given the decreased prevalence of occult bacteremia in the post-conjugate vaccine era, a less aggressive approach to the management of completely immunized, well-appearing, febrile (≥39ºC) children 3 to 36 months of age who do not have a focal source of infection appears reasonable [35,40,41]. (See 'Initial approach' below.)

A cost-effectiveness decision analysis of evaluation and management strategies for fever without a source (FWS) in the post-conjugate vaccine era considered negative aspects of diagnostic testing and treatment and used cases of meningitis and lives saved as outcome measures [42]. The management strategies evaluated were no work-up, clinical judgment, blood culture, blood culture plus antibiotics, WBC plus blood culture and antibiotics, and WBC plus selective blood culture and antibiotics. The following observations were noted:

Assuming a rate of pneumococcal bacteremia of >1.5 percent, WBC plus selective blood culture and antibiotics was the most cost-effective approach.

With a rate of pneumococcal bacteremia <0.5 percent, strategies that utilized empiric testing and treatment were no longer cost-effective.

At low rates of bacteremia, clinical judgment became more useful in selecting a high-risk population that might benefit from selective testing and treatment.

EVALUATION — The goal of the evaluation of the young, well-appearing, febrile child without an apparent source of infection is to identify a subtle bacterial infection and/or the risk of a more serious occult bacterial infection, both of which require further investigation and antibiotic therapy.

History — Historical features of a febrile illness that suggest an occult source of infection may be subtle and not immediately obvious to the caretakers. Therefore, a thorough history must include information about the child's functional status, including oral intake, presence of irritability or lethargy, and associated symptoms. The duration of fever appears to be a poor predictor of unsuspected bacteremia [43].

Specific questions regarding cough, vomiting, or change in activity should be included. As an example, children with pneumonia may have cough or tachypnea noted by a caretaker. Signs or symptoms of UTI (eg, dysuria, frequency, abdominal pain, back pain, new onset incontinence), should be specifically sought. Likewise, vomiting, with or without diarrhea, can occur in young children with UTI, and caretakers occasionally note that the urine is foul-smelling, although these symptoms are nonspecific. Finally, a young child with a deep soft tissue or bone infection may protect the affected area.

A careful history must identify any known underlying medical condition that increases the child's risk for serious infection, such as sickle cell disease or urinary tract reflux. In addition, the immunization history will greatly influence the subsequent evaluation, since the child who is incompletely immunized is at greater risk for occult bacteremia than the one who is completely immunized. (See 'Immunization status' above and 'Incomplete immunization' above.)

Physical examination — The child who is being evaluated for a subtle infection or fever without a source should be well-appearing. Febrile children who are acutely ill with symptoms, such as lethargy, poor perfusion, hypoventilation or hyperventilation, and cyanosis are said to appear toxic or septic. They are considered to have a significant bacterial infection until proven otherwise. Cultures of blood, urine, and CSF, when meningitis is suspected, should be obtained, intravenous fluid provided, antibiotic therapy initiated, and admission to the hospital arranged. (See 'Ill-appearing' below.)

Attention to abnormal vital signs and a thorough physical examination may identify a source of infection. Specific features to note include the following:

Tachycardia, tachypnea, or pulse oximetry ≤95 percent

Lesions in the oropharynx that may identify a recognizable viral illness, such as herpes gingivostomatitis (anterior ulcers) or Coxsackie virus (pharyngeal vesicles) (see "Soft tissue lesions of the oral cavity in children", section on 'Infections' and "Clinical manifestations and diagnosis of enterovirus and parechovirus infections" and "Herpetic gingivostomatitis in young children", section on 'Clinical features')

Increased work of breathing indicated by nasal flaring, retractions or use of accessory muscle, or focal lung findings, such as rales or decreased breath sounds

Abdominal tenderness

Pain with bone palpation or passive joint range of motion

Skin findings, such as petechiae, cellulitis, or viral exanthem

Laboratory testing — Testing in febrile children 3 to 36 months of age has been used to screen for the risk of bacterial infection as well as to diagnose specific infections. The decision to perform laboratory tests depends upon a variety of factors including age, immunization status, and obvious findings of infection (eg, otitis media, bronchiolitis, croup).

Recommendations regarding when to obtain specific tests are provided below. (See 'Initial approach' below.)

WBC and ANC counts — Several studies have identified an increased risk of occult pneumococcal bacteremia among unimmunized children with WBC ≥15,000/microL and absolute neutrophil count (ANC) ≥10,000/microL [33,44-46]:

A single center, prospective observational study of 1911 children, 3 to 36 months of age, who had fever without a source ≥39ºC (102.2ºF) and performed after introduction of Hib found that a WBC ≥15,000/microL had a sensitivity of 86 percent and a specificity of 77 percent for occult bacteremia [44]. The frequency of bacteremia in these patients was 1.5 percent (149/1911).

A multicenter, prospective observational study of 6579 children, 3 to 36 months of age, who had fever without a source ≥39ºC (102.2ºF) and performed after introduction of Hib found that a WBC ≥15,000/microL had a sensitivity of 80 percent and a specificity of 69 percent for occult bacteremia, and an ANC ≥10,000/microL had a sensitivity of 76 percent with a specificity of 78 percent [45]. In multivariate logistic regression analysis, ANC was an independent predictor of bacteremia with adjusted OR 1.15 (95% CI 1.06-1.25) for each 1000 cells/mm3 increase in the ANC. The frequency of bacteremia in this sample was 2.5 percent.

A multicenter retrospective observational study of 41,948 children, age 3 to 36 months, who had blood cultures performed after introduction of Hib and PCV7, found that a WBC ≤15,000/microL had a negative predictive value of 99.5 percent [33]. In this study, the frequency of bacteremia (1.6 percent) was less than blood culture contamination (1.8 percent).

Taken together, these studies suggest that a WBC >15,000/microL, while not ideal in screening for occult bacteremia, is helpful in determining which incompletely immunized children deserve blood culture and treatment in the post-conjugate vaccine era. However, these reports and others also have demonstrated that an elevated WBC, by itself, has both limited sensitivity and specificity as an indicator of SBI, particularly as other pathogens, such as S. aureus become more prominent isolates in children with bacteremia [33,47].

Urine tests — Multiple studies and two meta-analyses have evaluated screening tests for UTI [48,49]. In general, urine screening tests markedly improve the ability to detect UTI, but a urine culture should be sent in all young children in whom catheterized urine is obtained. The usefulness of dipstick, Gram stain, and microscopy is summarized in the table and discussed elsewhere (table 2). (See "Urinary tract infections in infants and children older than one month: Clinical features and diagnosis", section on 'Rapidly available tests'.)

Preliminary evidence also suggests that automated urine white blood cell (WBC) and bacteria counts can have high sensitivity and specificity for urinary tract infection in young children depending upon the thresholds used. As an example, in 342 febrile young children (median eight months of age) who had catheterized urine tested (12 percent with positive urine cultures), an automated bacterial count ≥250 cells/microL and an automated urine WBC count ≥100 cells/microL had sensitivities of 98 and 86 percent, respectively [50]. Point of care urine dipstick also had a high sensitivity (95 percent) suggesting that it is an acceptable alternative to automated urinalysis when rapid decision-making is necessary.

Cultures — The diagnosis of a SBI is often made with cultures, although the inherent delay between the initial evaluation of the patient and the availability of culture results complicates decisions regarding empiric antibiotic therapy.

Blood – Continuously monitored blood culture systems have decreased the length of time for a blood culture to turn positive. The mean time to positive blood cultures for pathogens is approximately 15 hours, compared with 31 hours for contaminants [51].

Urine – For the diapered child, urine for culture should be collected by catheterization, or in exceptional cases (eg, tight phimosis), suprapubic aspiration. Bag specimens should not be sent for culture because they are frequently contaminated. A clean catch is the preferred method of urine collection for culture in the child who is toilet-trained. The culture definition of UTI is discussed elsewhere. (See "Urine collection techniques in children" and "Urinary tract infections in infants and children older than one month: Clinical features and diagnosis", section on 'Diagnosis of UTI'.)

CSF – Children who are being evaluated for fever without a source should be well-appearing and therefore, not require lumbar puncture. That being said, CSF should be obtained from any patient with suspected meningitis. (See "Bacterial meningitis in children older than one month: Clinical features and diagnosis", section on 'Course'.)

Chest radiograph — A chest radiograph should be obtained in patients with tachypnea, respiratory distress, or oxygen saturation ≤95 percent. In addition, chest radiograph is suggested in children with WBC >20,000/microL even in the absence of these findings. (See 'Pneumonia' above.)

Inflammatory mediators — Preliminary evidence suggests that elevations in levels of inflammatory mediators (ie, C-reactive protein and procalcitonin) may be better markers of SBI than WBC and ANC in children at significant risk for bacterial infection, although the usefulness of these tests in practice is uncertain [52].

C-reactive protein (CRP) is an acute phase reactant released by the liver following inflammation or tissue damage. Observational studies that have evaluated CRP as a screening tool for occult bacterial infection report a wide range of sensitivity and specificity that vary by cutoff levels used to identify infants and children with SBI [53-57]. In addition, CRP concentrations generally do not increase until 12 hours after the onset of fever and can rise in both viral and bacterial infections [55].

Procalcitonin (PCT) levels rise in response to bacterial infections more rapidly than those of CRP. Limited preliminary data suggest that PCT levels may be more sensitive and specific markers for severe invasive bacterial infection in infants and children than WBC, ANC, and CRP [57-62]. However, in most clinical settings, PCT has limited availability.

A meta-analysis of five studies (1379 febrile children up to 36 months of age, including infants younger than three months) found that the diagnostic accuracy of C-reactive protein and procalcitonin were comparable for serious infection [63]. The optimal values for identifying a high risk of serious infection were ≥80 mg/L for C-reactive protein and ≥2 ng/mL for procalcitonin (sensitivity 40 to 50 percent, specificity 90 percent for each). Alternatively, the best values suggesting a low risk for serious infection were <20 mg/L for C-reactive protein and <0.5 ng/mL for procalcitonin (sensitivity >80 percent, specificity 70 percent for both).

Taken together, the evidence suggests that CRP and PCT are equivalent with respect to diagnostic accuracy. However, CRP is much more widely available than PCT and is thus more useful in clinical practice.

Molecular assays — Molecular assays based upon polymerase chain reaction, detection of bacterial 16S ribosomal RNA genes, or identification of host RNA signatures have shown potential in the rapid diagnosis of neonatal sepsis. However, these tests are not routinely available and require further validation before broad clinical implementation. (See "Evaluation and management of fever in the neonate and young infant (younger than three months of age)", section on 'Molecular assays'.)

The use of polymerase chain reaction for the detection of meningococcal disease is discussed in greater detail separately. (See "Diagnosis of meningococcal infection", section on 'Polymerase chain reaction'.)

INITIAL APPROACH — The evaluation and management of the febrile child 3 to 36 months of age without a source of infection must balance the consequences of not diagnosing a SBI with the decreasing prevalence of occult infection and the potential adverse effects of excessive testing and treatment [41]. Burdens of testing and expectant antibiotic therapy include false-positive results, adverse reactions to antibiotics, and, possibly, the effect of widespread antibiotic use on patterns of antibiotic resistance. The likelihood of SBI varies significantly by clinical appearance, age, and immunization status. (See 'Occult sources of infection' above.)

Well-appearing children 3 to 36 months of age, with fever ≥39ºC (102.2ºF), who have no underlying medical condition that would alter susceptibility to infection, and no focus of infection identified by a complete physical examination, are hereafter referred to as children with fever without a source (FWS).

Ill-appearing — Children who are ill-appearing or have unstable vital signs should be fully evaluated for serious infection with cultures of blood, urine, and, when meningitis is suspected, CSF. Those with tachypnea or leukocytosis (>20,000/microL) should have a chest radiograph. These patients should receive parenteral antibiotic therapy targeting the likely pathogens in this age group (S. pneumoniae, S. aureus, N. meningitidis, H. influenzae type b) and be admitted to the hospital.

Well-appearing

Immunization incomplete — The risk of occult bacteremia in incompletely immunized children is estimated to be as high as 5 percent (ie, what it was during the preconjugate vaccine era); the actual risk is probably somewhat lower because of "herd immunity." (See 'Immunization status' above and 'Impact of vaccines' above.)

Strategies for the evaluation and management of these children reflect the increased risk of bacteremia compared with completely immunized children and are drawn from experience and guidelines developed during the preconjugate vaccine era [4,30,31,33,44,51,64,65].

We suggest the following approach to evaluation of these children:

CBC with differential.

Blood culture should be obtained if the WBC is ≥15,000/microL. As a practical matter, the blood culture may be drawn with the CBC and sent if the WBC is ≥15,000/microL. Recognizing that WBC is not an ideal screening tool, some clinicians may prefer to always send a blood culture in these patients [33,39,42].

Urinalysis, and urine culture by bladder catheterization or in exceptional cases (eg, tight phimosis), suprapubic aspiration.

Chest radiograph in children with WBC ≥20,000/microL.

Children with an abnormal urinalysis should be treated for a urinary tract infection, although in questionable cases awaiting results of urine culture represents a reasonable alternative. (See "Urinary tract infections in infants and children older than one month: Acute management, imaging, and prognosis", section on 'Overview'.)

We recommend that children with FWS who are incompletely immunized who have a WBC ≥15,000/microL receive parenteral antibiotic therapy pending blood and urine cultures [4,42]. Ceftriaxone (50 mg/kg, intramuscularly) is preferred because of its antimicrobial spectrum and prolonged duration of action. Clindamycin (10 mg/kg, intravenously followed by oral clindamycin eight hours later) is one alternative for patients allergic to cephalosporins. Outpatient follow-up should occur within 24 hours. Patients in whom outpatient follow-up is uncertain should be admitted.

This strategy of selective treatment of high-risk children with FWS and WBC ≥15,000/microL is in agreement with the practice guidelines of the American Academy of Pediatrics and the American College of Emergency Physicians for children with FWS [4,66,67].

Support for treating patients 3 to 36 months of age with FWS and significant risk of bacteremia with empiric parenteral antibiotics is derived from meta-analyses and randomized trials performed before the routine availability of Hib, PCV7, and PCV13 conjugate vaccines [23,24,30].

A meta-analysis of four randomized controlled trials of 7899 children, age 3 to 36 months, who had a fever ≥39°C (102.2ºF), found that treatment of occult bacteremia with IM ceftriaxone reduced the chance of serious bacterial infections by approximately 75 percent (Number needed to treat (NNT) 17; OR 0.25; 95% CI 0.07-0.89) and that oral antibiotics were not effective [68].

A meta-analysis of prospective and retrospective studies of children age 3 to 36 months with fever without a source and bacteremia found that the mean probability of subsequent meningitis was 8.2 percent (all H. influenzae, type b) in patients treated with oral antibiotics and 0.3 percent in patients treated with parenteral antibiotics versus 9.8 percent in untreated children. No child treated with ceftriaxone developed culture-positive meningitis (0.3 percent; 95% CI 0.0-1.5 percent). The authors concluded that antibiotic therapy is effective in preventing meningitis [8].

A randomized, double blind, placebo controlled trial of 955 children between the ages of 3 to 36 months with fever ≥39ºC (102.2ºF) demonstrated no difference in major infectious morbidity between bacteremic children receiving oral amoxicillin (2 of 19) or placebo (1 of 8). The incidence of diarrhea was 15 percent in children receiving amoxicillin versus 11 percent in the placebo group (p = 0.10) [24]. The overall rate of bacteremia was 2.8 percent in this study.

An unblinded, randomized controlled trial of 6733 children between the ages of 3 to 36 months with fever ≥39ºC (102.2°F) also described an overall rate of bacteremia of 2.8 percent (195 of 6733) [30]. Five definitive focal infections (three meningitis, one pneumonia, and one sepsis) developed in the 3347 children receiving amoxicillin versus none in those treated with IM ceftriaxone (OR 0.0, 95% CI 0.0-0.5).

An unblinded, randomized trial of 96 children, between 6 and 24 months of age with a temperature >40ºC (104ºF), found that 4.3 percent of untreated patients (2 of 46) developed pneumococcal meningitis versus none of the 50 children treated with intramuscular aqueous penicillin G at the initial visit followed by oral penicillin for 10 days. Bacteremia was identified in 10.4 percent of all children [23].

Possible dermatologic adverse reactions were more commonly seen in the ceftriaxone group (8.7 versus 4.9 percent), but gastrointestinal complaints, such as diarrhea, were not different (14.5 versus 15.0 percent). No anaphylaxis was seen in either group.

Taken together, these studies indicate that unimmunized children with FWS avoid progression of bacteremia to focal infections, especially meningitis, when treated with parenteral antibiotics. Given the increasing prevalence of penicillin resistant S. pneumoniae, intramuscular ceftriaxone remains a preferred parenteral agent.

Immunization complete — A child with FWS who is completely immunized has a risk of bacteremia that is <1 percent. Decision analysis suggests that at this low risk, laboratory evaluation and empiric antibiotic therapy do not significantly alter the likelihood of progression to focal bacterial infection and are not indicated [42,69]. (See 'Immunization status' above and 'Impact of vaccines' above.)

However, the risk of UTI as an occult source of infection remains substantial in fully immunized children, depending on age, gender, and circumcision status [41]. This risk guides recommendations for evaluation and treatment in these patients [68].

For children over six months of age with FWS who are completely immunized, we suggest that girls less than 24 months of age and uncircumcised boys less than 12 months receive a urinalysis and urine culture. Urine for culture should be collected by catheterization or, in exceptional cases (eg, tight phimosis or severe labial adhesions), suprapubic aspiration. Bag specimens should not be sent for culture because they are frequently contaminated. (See "Urine collection techniques in children" and 'Urinary tract infection' above.)

For girls >24 months of age, uncircumcised boys >12 months of age and circumcised boys >6 months of age, all of whom have been completely immunized, we do not suggest routine laboratory evaluation or presumptive treatment with antibiotics. However, urinalysis and urine culture should be obtained in those with signs or symptoms of UTI, which must be specifically sought (eg, dysuria, frequency, abdominal pain, back pain, new onset incontinence). In addition, children with a prior history of UTI, urogenital anomalies, or prolonged fever (>48 hours) warrant urinalysis and urine culture. (See 'Urinary tract infection' above.)

Some experts suggest that a high fever without a source (>39°C [102.2°F]) is sufficient justification for urine culture on the first visit in uncircumcised boys 12 to 24 months of age (algorithm 1). (See "Urinary tract infections in infants and children older than one month: Clinical features and diagnosis", section on 'Decision to obtain'.)

Children with FWS who are completely immunized against Hib and either PCV7 or PCV13, meet criteria for urine testing, and have an abnormal urinalysis should be treated for UTI. Appropriate follow-up should be arranged. (See "Urinary tract infections in infants and children older than one month: Acute management, imaging, and prognosis", section on 'Overview'.)

Despite the high risk for UTI and low risk for bacteremia among fully immunized children, evidence suggests that some emergency department (ED) clinicians may not utilize laboratory testing and antibiotic therapy appropriately when caring for these patients. As an example, between 2006 and 2008, estimates regarding laboratory testing and antibiotic treatment extrapolated from 1600 ED visits by fully immunized febrile children 6 to 36 months of age in the United States were as follows [70]:

No testing was performed in 59 percent

Complete blood counts were obtained in 21 percent

Urine testing was not performed in an estimated 60 percent of girls with high fever

Antibiotics were prescribed in an estimated 20 percent of patients in whom no testing was performed

These estimates suggest that urine testing may be underutilized while measurement of complete blood count and antibiotic treatment may be overutilized in these patients.

FOLLOW-UP — Follow-up should be arranged within 24 hours for those children with fever without a source (FWS) who have received parenteral antibiotics. Patients who are not treated with antibiotics should be instructed to seek medical attention within 48 hours if they have persistent fever.

Careful instructions should be given to caretakers to return immediately if fever becomes higher, the patient looks sicker, or local symptoms or signs develop (eg, cough, diarrhea, cellulitis).

Positive blood cultures — An organism may not be identified definitively for 24 to 48 hours after the blood culture becomes positive, making management decisions difficult. The clinical appearance of the child and the Gram stain of the organism can be useful in deciding whether or not the child should be admitted to the hospital. Consultation with the microbiology laboratory personnel and/or an infectious disease consultant may be helpful in narrowing the list of potential organisms and the likelihood that the findings represent a pathogen. Patients with a positive culture that is felt to be a pathogen should be reevaluated and managed according to appearance, persistence of fever, and specific isolate (algorithm 2).

The main goal is to identify and avoid progression to serious bacterial infection, especially meningitis:

S. pneumoniae

Febrile – In a retrospective observational study prior to PCV7 availability, 548 children with a blood culture positive for S. pneumoniae had outcomes examined. Children who were well, but persistently febrile at the revisit and did not receive antibiotics at the initial visit had a 33 to 42 percent chance of infection (primarily persistent bacteremia) and a 4.4 percent chance of meningitis [65]. Meningitis developed despite initial oral antibiotic therapy in 2 of 49 children (4 percent). Because of this high risk of SBI, patients with a blood culture positive for S. pneumoniae who are febrile on revisit should undergo a full sepsis evaluation (including lumbar puncture). They should also receive parenteral antibiotics tailored to the isolate's susceptibility or to the community susceptibility pattern for S. pneumoniae if the culture susceptibility is not yet available.

These children may receive continued antibiotic therapy as an outpatient for 7 to 10 days with close follow-up if CSF findings show no evidence of meningitis. Antibiotic regimens should provide coverage for resistant S. pneumoniae. Possibilities include high dose oral amoxicillin (30 mg/kg per dose, three times daily; maximum dose: 3 g daily), oral amoxicillin-clavulanate 45 mg/kg per dose twice daily (maximum dose of amoxicillin: 3 g daily), or clindamycin 10 mg/kg per dose three times daily in penicillin allergic patients.

Afebrile – Well-appearing, afebrile children who did not receive antibiotics at the initial visit and who have a blood culture positive for S. pneumoniae have an approximately 9 percent risk of persistent bacteremia [65]. These patients can be managed with antibiotics as an outpatient with close follow-up. Another blood culture should be drawn before further antibiotic therapy is initiated. Antibiotic regimens should provide coverage for resistant S. pneumoniae. Possibilities include high dose oral amoxicillin (30 mg/kg per dose, three times daily; maximum dose: 2 to 3 g daily), oral amoxicillin-clavulanate (45 mg/kg per dose, twice daily; maximum dose: 3 g total daily dose of amoxicillin), or clindamycin (10 mg/kg per dose, three times daily) in penicillin allergic patients.

Other pathogens — The limited data for bacteremia caused by organisms other than S. pneumoniae suggests that outpatient therapy with oral antibiotics does not prevent serious bacterial infection, even in well-appearing, afebrile children. In addition, the risk of meningitis is presumed to be high for patients with N. meningitidis bacteremia.

For these reasons, hospital admission and parenteral antibiotic therapy is suggested for children with a blood culture that is positive for N. meningitidis, H. influenzae type b, S. aureus, gram-negative rods, or other pathogens. A lumbar puncture should be performed if meningitis is clinically suspected. CSF evaluation is also recommended for patients with blood culture positive for N. meningitidis and for young infants (three to six months of age) with Group B Streptococcus bacteremia. Well children over three months of age with a blood culture positive for E. coli or S. aureus do not need a lumbar puncture.

Probable blood culture contaminant — With the decline in the prevalence of occult bacteremia, it is now more likely that a blood culture will be positive for a contaminant than for a pathogen [31-33,51]. Certain microbiologic features, such as slow growth or Gram stain, showing either gram-positive rods or gram-positive cocci that are coagulase negative, suggest a contaminant. Consultation with the microbiology laboratory and/or an infectious disease specialist may be useful when preliminary results are unclear.

Molecular assays can help rapidly detect Staphylococcus aureus, including methicillin-resistant strains in blood cultures positive for gram-positive cocci in clusters. (See "Rapid detection of methicillin-resistant Staphylococcus aureus", section on 'Blood cultures'.)

The child who is well on follow-up, afebrile, and has an isolate from blood culture that is a likely contaminant can be followed without antibiotic treatment, pending the final identification of the organism.

Children who are not well on follow-up or continue to have fever should be reevaluated and the assumption that the positive blood culture represents a contaminant should be reevaluated (algorithm 2). (See 'Positive blood cultures' above.)

Positive urine culture — Children with a positive urine culture should be treated for UTI. (See "Urinary tract infections in infants and children older than one month: Acute management, imaging, and prognosis", section on 'Overview'.)

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Basics topic (see "Patient information: Fever in children (The Basics)")

Beyond the Basics topic (see "Patient information: Fever in children (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

General issues

The following recommendations apply to well-appearing children 3 to 36 months of age, with fever ≥39ºC (102.2ºF), who have no underlying medical condition that would alter susceptibility to infection, and no focus of infection identified by a complete physical examination, hereafter referred to as children with fever without a source (FWS). (See 'Background' above.)

The majority of children with fever have either a self-limited viral infection or a recognizable source of bacterial infection. (See 'Occult sources of infection' above.)

Serious bacterial infections that occur in children 3 to 36 months of age include meningitis, pneumonia, and focal skin infections.

Subtle sources of infection, such as pneumonia or osteomyelitis, can sometimes be identified with a careful history and physical examination.

Relatively common occult sources of infection include pneumonia and urinary tract infections (UTIs), with occasional cases of bacteremia.

A thorough history, including immunization status and complete physical examination, should be performed in all febrile children to identify obvious and subtle focuses of infection. (See 'History' above and 'Physical examination' above.)

Ill-appearing child

Children who are ill-appearing or have unstable vital signs require full evaluation for serious infection with cultures of blood, urine, and when meningitis is suspected, CSF. A chest radiograph should be obtained in patients who have tachypnea or respiratory distress and is warranted for those with WBC ≥20,000/microL, even in the absence of physical findings of pneumonia. (See 'Ill-appearing' above.)

Children who are ill-appearing or have unstable vital signs should receive parenteral antibiotic therapy targeting the likely pathogens in this age group (S. pneumoniae, S. aureus, N. meningitidis, H. influenzae type b) and be admitted to the hospital. (See 'Ill-appearing' above.)

Well-appearing child

Incompletely immunized

For children with FWS who have not been completely immunized, we suggest the following tests:

CBC with differential: A blood culture should be sent for those with WBC ≥15,000/microL. Some clinicians may choose to send a blood culture for all patients. (See 'Immunization incomplete' above.)

Urinalysis and urine culture by bladder catheterization or, in exceptional cases (eg, tight phimosis or severe labial adhesions), suprapubic aspiration. (See 'Urine tests' above and 'Immunization incomplete' above.)

Chest radiograph when WBC ≥20,000/microL. (See 'Immunization incomplete' above.)

We recommend that incompletely immunized children with FWS and WBC ≥15,000/microL receive parenteral antibiotic therapy pending culture results (Grade 1B). A single dose of intramuscular ceftriaxone (50 mg/kg) is preferred because of its antimicrobial spectrum and duration of action. (See 'Immunization incomplete' above.)

These patients should be seen for follow-up by their primary care provider within 24 hours. An alternative is to follow-up in the emergency department if a regular source of primary care is unavailable. (See 'Follow-up' above.)

Completely immunized

For children >6 months of age with FWS who are completely immunized, we suggest that girls <24 months of age and uncircumcised boys <12 months receive a urinalysis and urine culture. Urine for culture should be collected by catheterization or, in exceptional cases (eg, tight phimosis or severe labial adhesions), suprapubic aspiration. Bag specimens should not be sent for culture because they are frequently contaminated. (See 'Urinary tract infection' above and "Urine collection techniques in children".)

For girls >24 months of age, uncircumcised boys >12 months of age and circumcised boys >6 months of age with FWS, all of whom have been completely immunized, we do not suggest routine laboratory evaluation. In addition, these children should not receive presumptive treatment with antibiotics (Grade 1B). However, urinalysis and urine culture should be obtained in those at high risk for UTI. (See 'Urine tests' above and 'Immunization complete' above.)

Completely immunized children with fever ≥39°C (102.2°F) and an abnormal urinalysis should be treated for a urinary tract infection. (See 'Immunization complete' above and "Urinary tract infections in infants and children older than one month: Acute management, imaging, and prognosis", section on 'Antibiotic therapy'.)

Clinical follow-up

We recommend that children with fever that persists for more than 48 hours or with a deterioration in clinical condition undergo repeat medical evaluation.

Culture follow-up

Urine cultures

Patients with a positive urine culture require treatment tailored to the identified organism and their clinical status. (See "Urinary tract infections in infants and children older than one month: Acute management, imaging, and prognosis", section on 'Overview'.)

Blood cultures

Children of 3 to 36 months of age with a positive blood culture for a presumed pathogen require reevaluation and management based on their appearance, persistence of fever, and specific isolate (algorithm 2). (See 'Positive blood cultures' above.)

We suggest that the child who is well on follow-up, afebrile, and has an isolate from a preliminary report of a blood culture that is a likely contaminant, be followed on a daily basis as an outpatient without antibiotic treatment, pending the final identification of the organism (Grade 2C). (See 'Probable blood culture contaminant' above.)

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