Pediatric Fever Without a Source - Infant

Authors: Hemal Kanzaria, MD, Christine Cho, MD, Andi Marmor, MD, Ellen Laves, MD, Michelle Lin, MD
Updated: 2/9/2012

Pediatric Fever Without a Source: 29 Days - 3 Months

Fever defined as temperature ≥ 38°C / 100.4 °F (rectal)

Viral URI symptoms do NOT count as a fever source in this age group.

  • While RSV+ infants have a decreased serious bacterial infection risk, rate of concurrent UTI = 5.5%.


History and physical are not reliable to rule-out serious bacterial infection

Serious bacterial infections include

  • Urinary tract infection (up to 15%)
  • Bacteremia (1%)
  • Meningitis (0.2-0.4%)
  • Others:
  • Gastroenteritis
  • Osteomyelitis
  • Pneumonia
  • Septic joint
  • Soft tissue infection


  • More common:
    • E. coli
    • Group B Strep
    • S. pneumo
  • Less common:
    • N meningitides
    • H flu (type B)
    • Staph aureus


  • Pyelonephritis: Diagnosis made, if positive for LE or nitrites, or >10 WBC/hpf
  • Caution: Serum WBC does NOT predict meningitis (Bonsu, Annals EM, 2003)

"Low Risk Infant" Criteria and Workup

  • Rochester and Philadelphia criteria apply only to the age group of 29-60 days.
  • Boston criteria applies to the age group of 29-90 days.

Rochester Criteria


  • Term infant
  • No perinatal antibiotics
  • No underlying disease
  • Not hospitalized longer than mother


  • Well-appearing
  • No ear, soft tissue, or bone infection


  • WBC 5K-15K
  • Absolute band count <1.5K
  • Urine ≤10 WBC/hpf
  • Stool ≤5 WBC/hpf

Philadelphia Criteria


  • Immunocompetent


  • Well-appearing
  • Unremarkable exam


  • WBC <15K
  • Band-neutrophil ratio <0.2
  • Urine <10 WBC/hpf
  • Urine gram stain negative
  • CSF <8 WBC
  • CSF gram stain negative
  • Stool (if diarrhea): No blood, few or no WBC on smear


  • No infiltrate

Boston Criteria


  • No immunizations within last 48 hr
  • No antibiotics within last 48 hr
  • Not dehydrated


  • Well-appearing
  • No ear, soft tissue, or bone infection


  • WBC <20K
  • Urine <10 WBC/hpf
  • CSF <10 WBC/hpf
  • CXR: no infiltrate

All recommend the following minimum workup

  • CBC
  • Catheterized UA
  • Urine culture

Is further workup or antibiotics indicated?

Criteria Blood Culture CXR LP Abx
Rochester If abnormal serum WBC If respiratory sx If abnormal serum WBC No
Philadelphia Required Required Required No
Boston Required If respiratory sx Required Yes

SUGGESTED WORKUP varies by provider and local practices

Generally accepted workup includes:

  1. CBC with differential
  2. Blood cultures
  3. Catheterized urinalysis and urine culture (or via suprapubic tap)
  4. Consider: CSF studies, if ill-appearing infant

  5. NOTE: Strongly consider performing LP, if giving antibiotics (cell count, glucose, protein, gram stain, culture, extra tube to hold for potential other studies)

  6. Consider: Stool culture (if diarrhea)

  7. Consider: CXR and rapid viral testing (if respiratory sx or increased work of breathing)


Low risk infant: Must have a reliable caregiver who can return in 24 hours

  • Options for management:

    • No antibiotics and close follow-up in 24 hrs
    • Ceftriaxone IV/IM after LP with close follow-up in 24 hrs

High risk infant: Admit to hospital for ceftriaxone IV/IM and closer observation


  • Ishimine P. The evolving approach to the young child who has fever and no obvious source. Emerg Med Clin North Am. 2007;25(4):1087-115, vii. [PubMed]