Fever is one of the most common complaints of children presenting to the emergency department (ED). In fact, children typically have four to six febrile illnesses in the first two years of life. In most cases, the etiology of the fever is either a benign, nonspecific viral infection or a self-limited focal bacterial infection such as otitis media or streptococcal pharyngitis. However, parents and practitioners are always concerned with the possibility of an underlying serious condition, such as meningitis or sepsis, and therefore often approach the febrile child with some degree of trepidation. In addition, the evaluation of the febrile child is complicated by age-related variations such as the patient’s ability to communicate, immune system development, and immunization status. Therefore, it is important for the practitioner to understand the underlying pathophysiology of fever, the risk factors associated with serious bacterial illness (SBI), and the relative frequency of certain sepsis and sepsis-like conditions to develop a rational approach to management, including the appropriate use of laboratory testing and antibiotics.

The evaluation of the febrile child is often determined on presentation by the age of the child, the presence of underlying chronic illness, or immunocompromise. Due to the relative lack of clinical signs and an immature immune system, neonates have specific age-appropriate management strategies (see Chapter 2). However, there is practice variation for 28- to 56-day-old infants. They are either included with neonates or are considered as a separate group and managed uniquely. Fever may be the only presenting symptom of SBI in children with underlying illnesses such as sickle cell disease, immunodeficiency, or cancer, as well as those children with indwelling devices such as a ventriculoperitoneal shunt or a central line. Therefore, the presence of fever in these children often requires laboratory testing and empiric antibiotic treatment until bacterial infection can be ruled out. However, the majority of well-appearing, otherwise healthy children require only a thorough history and physical examination, and in the absence of a bacterial source of infection can be managed with antipyretic therapy and observation until the course of the illness resolves. This chapter deals specifically with the otherwise healthy febrile child between the ages of 1 month and 3 years.

Normal body temperature is generally considered to be 98.6°F (37°C). However, body temperature varies with age, time of day, gender, and other host-specific factors. In addition, non-disease causes of variation include bundling, elevated ambient air temperature, and exercise. Thus there is no true single value for normal body temperature. However, as an effort to standardize protocols and guidelines, fever in young infants and children is often defined as a body temperature greater than 100.4°F (38°C) rectally.^1,2

The anatomic site at which the temperature is taken also affects measurement. Significant variation may occur between temperatures measured externally (axillary) and those measured closer to core areas (rectal), which more accurately and consistently reflect overall body temperature status. Sites other than rectal, such as axillary, oral, tympanic, temporal, or skin, as well as use of other devices, such as infrared or liquid crystal, are more convenient and less invasive. They may serve as effective screening tools but are generally less accurate in the young infant and child and tend to underestimate body temperature.^3–5

Parents often rely on palpation to detect the presence of fever, even if they own a thermometer.⁶ Although this subjective measure has a sensitivity of over 75%, the low specificity tends to overestimate the actual presence of fever.⁴ Thus, while “fever to touch” may be useful to exclude its presence, parental perception of fever should still be taken seriously by the clinician.⁴

Body temperature is tightly regulated. Increases above normal are termed either hyperthermia, if environmentally produced, or fever. Maintenance of body temperature involves a complex interplay of autonomic, endocrinologic, and behavioral mechanisms. The thermoregulatory center is located in the preoptic region of the hypothalamus and maintains the body’s “set point.” Damage to this area may result in extreme body temperature variations.

Fever is a host response to combat infection. Exogenous pyrogens are released during viral or bacterial invasion. These pyrogens elicit a complex cascade of processes that result in the elevation of the set point in the thermoregulatory center. As a response, the body increases heat generation and heat conservation to increase the body temperature to the new set point. Since this process takes many minutes to raise the core temperature, it is not unusual to see rigors (shivering, cool extremities due to vasoconstriction) before the detection of fever at a peripheral site. A summary of the febrile response is shown in Figure 3-1.

Much focus has been placed on the height and duration of fever as a predictor of SBI. Although the height of the fever is often considered a worrisome sign by parents and clinicians alike, in an otherwise healthy child even temperatures of >39°C have relatively low sensitivity (10%–14%) and predictive value (4%–40%) for serious illness in infants over 6 months and limited usefulness in infants 3 to 6 months.⁴ Therefore, the height of fever is not an accurate marker of SBI in febrile children.⁷ In fact, other clinical signs such as age, appearance, and peripheral perfusion are better predictors. Similarly, although there may be a weak converse association between duration of fever and bacteremia, overall, the duration of fever is a poor predictor of SBI.⁴ Finally, the change in temperature 1 to 2 hours after antipyretic administration does not help identify children with SBI.^4,8,9 However, antipyretic response may allow the clinician to better assess the child’s clinical state and therefore aid in determining which child is at risk for SBI.

Fever is often a source of anxiety for both parents and clinicians. Parents are often overly concerned with the presence of fever, fearing seizures or brain damage, and do not understand the beneficial aspects. Likewise, clinicians may fear missing the rare occurrence of serious illness or succumb to parental pressure to perform laboratory tests and provide empiric antibiotics. In fact, parents who are “very worried” about fever are more likely to bring their child for medical evaluation, more likely to have blood tests performed on their child, and more likely to perceive their doctors to be very worried about fever.¹⁰ Furthermore, parental fears are often exaggerated by misconceptions about the effects of fever, including the risk of brain damage.^11,12 Parental education should therefore attempt to provide parents with an understanding of the use of antipyretics to treat symptoms and not to cure the disease. When possible, parents should also be brought to understand the recurrent nature of fever and the lack of relationship of height of temperature to the presence of serious illness. In fact, many health care providers believe that the risk of heat-related adverse outcomes during a simple febrile illness is increased with temperatures above 40°C, although this belief is not justified.⁹ The likelihood of a benign viral illness as the cause for most febrile illness in infants and children should be stressed. Significant parental coaching is often warranted to avoid over- or under-evaluation and treatment. In addition, during the course of the illness, parents should be instructed to monitor the child’s clinical state and the appearance of new or worsening symptoms as indicators of when to follow up with their medical provider.

Pediatric sepsis is a common cause of death in infants and children worldwide and may be caused by bacterial, viral, parasitic, or fungal organisms. Although most infections are contained by a local inflammatory response, occasionally the host response is of a more widespread nature, characterized by the dissemination of inflammatory cytokines and resultant activation of the immune system systemically. The clinical symptoms of this systemic inflammatory response syndrome (SIRS) include temperature instability, age-inappropriate tachycardia or tachypnea, as well as an abnormal leukocyte count. Sepsis is defined as SIRS in response to an infectious process. Severe sepsis includes sepsis-induced organ dysfunction or tissue hypoperfusion resulting in hypotension, liver dysfunction, changes in mental status, and elevated lactate. Septic shock is severe sepsis with hypotension that does not respond to intravenous fluid administration alone. Thus there is a continuum from infection to bacteremia, SIRS, severe sepsis, septic shock, and finally multi-organ dysfunction syndrome (MODS). When assessing febrile young infants and children, the goal is to determine which of the above conditions apply or whether it is a self-limited viral illness. Because decompensation can be rapid, there is increased emphasis on the importance of stopping sepsis, which requires early identification of those children who manifest early signs of SIRS and severe sepsis in an effort to begin goal-directed treatment promptly with intravenous fluids, antibiotics, and pressors if needed.¹³

Early studies on fever noted that approximately 3% of well-appearing children (3–36 months old), who were initially managed as outpatients, had bacteremia.^14,15 Up to 80% of bacteria isolated in these studies were represented primarily by S. pneumoniae, and to a lesser degree, H. influenzae type B and Neisseria meningitides. Although the vast majority of these cases of “occult” or “unsuspected” bacteremia resolved spontaneously without antibiotic therapy, the concern that a small percentage would develop SBI (e.g., meningitis, osteomyelitis, or pneumonia) led to various policies advocating routine laboratory testing and selective use of empiric antibiotics for febrile, well-appearing young children without an identifiable source of infection. However, presumptive antibiotic therapy has not been shown to prevent this occult bacteremia.^14–15

Widespread vaccination for H. influenzae type B and S. pneumoniae has had a profound impact on the incidence of occult bacteremia. Pneumococcal bacteremia has been reduced to less than 0.2% in vaccinated healthy children but remains at about 1% to 1.5% in unimmunized children.^16–18 Therefore, based on the existing data, it appears that for the well-appearing, otherwise healthy febrile young child with no source of infection, the risks and costs of routine testing and empiric antibiotic therapy likely exceed the potential benefit.¹⁵ In fact, over the past decade there has been a national decline in obtaining a complete blood count (CBC), as well as a trend toward fewer blood cultures in the evaluation of children 2 to 24 months presenting to the ED with fever and no source of infection.¹⁹ Given the extremely low risk of bacteremia and its sequelae, the best expectant therapy in the well-appearing child is close observation by a reliable caretaker.