Febrile neonates and young infants

Evaluation of the Febrile Child, Sepsis & Meningococcal Disease

Fever is among the most frequent clinical presentations in paediatric medicine. While the vast majority of febrile episodes reflect benign, self-limiting viral infections, fever may be the solitary herald of a serious bacterial infection (SBI) such as occult bacteraemia, bacterial meningitis, urinary tract infection, or fulminant meningococcal sepsis. In Australia, the routine implementation of conjugate vaccines against Streptococcus pneumoniae, Haemophilus influenzae type b (Hib), and Neisseria meningitidis has reshaped the epidemiology of paediatric infection, making age-stratified clinical evaluation and rapid recognition of red-flag signs paramount.

Age-Stratified Risk of Serious Bacterial Infection (SBI)

An infant's immunological competence evolves rapidly during the first months of life. Physiological immaturity of neutrophil function, complement cascades, and cell-mediated immunity places young infants at heightened risk of rapid, overwhelming systemic bacterial invasion.

1. Febrile Neonates (Age Under 28 Days)

• Infection Risk: Approximately 10% to 15% of febrile neonates harbor an SBI. Clinical signs of systemic sepsis in this age group are notoriously subtle, non-specific, and unreliable: hypothermia or fever ($\ge 38.0^\circ\text{C}$), subtle lethargy, poor feeding, weak suck, tachypnoea, irritability during handling, or jaundice.
• Pathogen Profile: Perinatal pathogens acquired during passage through the birth canal or ascending uterine infection:
  • Group B Streptococcus (Streptococcus agalactiae): Leading cause of neonatal sepsis and meningitis.
  • Escherichia coli (and other enteric Gram-negative bacilli): Frequent cause of urosepsis and meningitis.
  • Listeria monocytogenes: Transplacental or intrapartum acquisition causing granulomatosis infantiseptica, sepsis, and meningitis.
  • Herpes Simplex Virus (HSV-1 / HSV-2): Manifests on days 5 to 21 with mucocutaneous vesicles, central nervous system encephalitis, or disseminated multiorgan failure with coagulopathy.
• Mandatory Diagnostic Workup: ALL febrile neonates require immediate hospital admission and a full septic screen regardless of clinical appearance:
  • Blood cultures, full blood count, C-reactive protein (CRP), and serum procalcitonin.
  • Urine microscopy and culture: Collected strictly via sterile urethral catheterisation or suprapubic bladder aspiration (SPA). Bagged urine specimens carry a false-positive contamination rate exceeding 50% and are completely unacceptable for diagnosing neonatal urosepsis.
  • Lumbar Puncture (LP): Essential to evaluate cerebrospinal fluid (CSF) cell count, protein, glucose, Gram stain, bacterial culture, and viral PCR (HSV, enterovirus, parechovirus).
  • Chest radiography: If respiratory distress, tachypnoea, or abnormal auscultatory findings are present.
• Empirical Inpatient Antibiotic Therapy:
  • Intravenous Ampicillin or Amoxicillin ($50\text{ mg/kg}$ IV 8-hourly) to cover Listeria monocytogenes and Enterococcus species;
  • PLUS Intravenous Cefotaxime ($50\text{ mg/kg}$ IV 8-hourly) or Intravenous Gentamicin ($4\text{ to }5\text{ mg/kg}$ IV daily) to cover Gram-negative coliforms (E. coli) and Group B Streptococcus.
  • Add intravenous aciclovir ($20\text{ mg/kg}$ IV 8-hourly) if maternal HSV history, seizures, CSF pleocytosis, or mucocutaneous vesicles are present.
• Ceftriaxone in neonates: Avoid in relevant premature, hyperbilirubinaemic or IV-calcium-exposed neonates under product information and the neonatal protocol. Cefotaxime is commonly preferred for neonatal meningitis; do not prescribe by an oversimplified adult age rule.

2. Young Infants (Age 1 to 3 Months / 29 to 90 Days)

• Young febrile infants: Apply one validated age-appropriate pathway with senior input. Do not mix thresholds from Rochester, PECARN and older-infant rules. A positive viral test reduces some risks but does not exclude UTI or invasive infection and cannot alone justify discharge.
  • Clinically well-appearing, normal cry, interactive, normal peripheral perfusion.
  • Previously healthy, term gestation ($\ge 37\text{ weeks}$), no prior hospitalisations or chronic illness.
  • No focal bacterial infection on examination (excluding viral otitis media or clear bronchiolitis).
  • Laboratory markers: Peripheral white cell count $5.0\text{ to }15.0 \times 10^9/\text{L}$, absolute neutrophil count $< 10 \times 10^9/\text{L}$, normal urinalysis ($< 10\text{ WBC/hpf}$ on catheterised specimen), and normal CRP/procalcitonin.
• Management:

3. Children Aged 3 to 36 Months

• Epidemiology: Routine Australian immunisation with the 13-valent pneumococcal conjugate vaccine (PCV13) and Hib vaccine has reduced occult bacteraemia rates in well-appearing children to $< 0.5\%$.
• Urinary Tract Infection (UTI): The most common occult serious bacterial infection in this age bracket (occurring in ~5% of febrile girls and ~2% to 3% of boys under 1 year).
  • Clinical Features: Unexplained fever, irritability, vomiting, foul-smelling urine, poor feeding.
  • Diagnostic Collection: In toilet-trained children, a clean-catch midstream urine is appropriate. In non-toilet-trained infants, clean-catch urine is attempted first; if clean-catch is impossible or the child is acutely unwell, urethral catheterisation is performed.
  • Microscopic Definition: Significant pyuria ($> 10\text{ to }100 \times 10^6\text{ leukocytes/L}$) and single-organism bacteriuria ($> 10^5\text{ CFU/mL}$ for clean catch, $> 10^4\text{ CFU/mL}$ for catheter specimen, or any growth on suprapubic aspiration).

Primary references (checked 7 October 2026): RCH Kawasaki disease; RCH meningitis/encephalitis.