Approach to fever without a source in children 3 to 36 months of age, either unimmunized or incompletely immunized*

MIS-C: multisystem inflammatory syndrome in children; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; URI: upper respiratory infection; CBC: complete blood count; WBC: white blood cell; ANC: absolute neutrophil count; LE: leukocyte esterase; HPF: high-power field; UTI: urinary tract infection; COVID-19: coronavirus disease 2019; MIS-C: Multisystem Inflammatory Syndrome in Children.
* Incomplete immunization means that the child has not received the primary series of 3 immunizations with conjugate vaccines against Streptococcus pneumoniae (PCV7 or PCV13) and at least 2 or 3 doses, depending upon vaccine formulation, of Haemophilus influenzae type B (Hib).
¶ If results are rapidly available (eg, within 60 minutes), a serum procalcitonin level identifies invasive bacterial illness with higher sensitivity and specificity than WBC or ANC. A procalcitonin level >0.5 ng/mL warrants the same management as a WBC ≥15,000/microL or an ANC ≥10,000/microL. Refer to UpToDate topics on fever without a source in children 3 to 36 months of age.
Δ To avoid multiple blood draws, the blood culture may be drawn with the CBC and sent if the WBC or ANC is elevated. Recognizing that these studies are not ideal screening tools, some clinicians may prefer to always send a blood culture in these patients.
◊ Refer to UpToDate content on empiric treatment of UTI in children.
§ Ceftriaxone (50 mg/kg, intramuscularly) is preferred because of its antimicrobial spectrum and prolonged duration of action. Refer to UpToDate content on treatment of children with fever without a source.