Fever in Infants and Children

Fever in Infants and Children: Definition & Pathophysiology - Hot Topic Basics

• Definition: Fever is a core body temperature ≥ 38°C (100.4°F), typically measured rectally.
• Pathophysiology:
  • Exogenous pyrogens (e.g., microbes, toxins) stimulate release of endogenous pyrogens (cytokines: IL-1, IL-6, TNF-α).
  • Cytokines act on the hypothalamus, increasing Prostaglandin E2 (PGE2) synthesis.
  • PGE2 elevates the hypothalamic thermoregulatory set-point, leading to increased body temperature.

⭐ Rectal temperature is the gold standard for core temperature measurement in infants and young children.

Fever in Infants and Children: Etiology - Culprit Hunt Time

• Viral Infections: Most frequent cause (e.g., URI, gastroenteritis, RSV, influenza).
• Bacterial Infections (Serious Bacterial Infection - SBI):
  • Key concerns: UTI (esp. E. coli), pneumonia, bacteremia/sepsis, meningitis.
• Common Bacterial Culprits by Age:

  Age Group	Key Pathogens
  Neonates (<28 d)	GBS, E. coli, Listeria monocytogenes
  1-3 months	Above + S. pneumoniae, Hib (unimmunized)
  >3 mo - 36 mo	S. pneumoniae, N. meningitidis, Salmonella spp.

⭐ Most common cause of Fever Without a Source (FWS) in children <3 years is viral infection. However, Serious Bacterial Infection (SBI) must be diligently ruled out in younger infants, particularly those <3 months old (highest risk).

Fever in Infants and Children: Evaluation & Red Flags - Spotting Danger Signals

• Evaluation: History (exposure, immunisation, sick contacts), complete exam (VS, hydration, perfusion, identify focus).
• Red Flags: Age <3 mo (esp. <28 days), toxic appearance (📌 TICLS: Tone, Interactiveness, Consolability, Look/Gaze, Speech/Cry), Temp >40°C or <36°C (infants), petechiae/purpura, poor perfusion (cap refill >2s), cyanosis, respiratory distress, bulging fontanelle, seizures, inconsolable cry.
• Age-Based Workup:

⭐ Any infant <28 days with fever (≥38°C) requires full sepsis evaluation (blood, urine, CSF cultures) and empiric IV antibiotics.

Fever in Infants and Children: Management - Cooling The Flames

• Supportive care:
  • Adequate hydration.
  • Light clothing.
  • Tepid sponging (lukewarm water, avoid shivering).
• Antipyretics:
  • Paracetamol: 10-15 mg/kg/dose (PO/PR) q4-6h. Max: 75 mg/kg/day.
  • Ibuprofen: 5-10 mg/kg/dose (PO) q6-8h for >6 months. Max: 40 mg/kg/day.

⭐ The primary goal of antipyretics is to improve child's comfort, not solely to normalize temperature; alternating antipyretics is not routinely recommended.

Fever in Infants and Children: Special Syndromes - Fever's Curveballs

• Febrile Seizures:
  • Simple vs. Complex Criteria:

    Feature	Simple FS	Complex FS
    Type	Generalized	Focal
    Duration	<15 min	>15 min
    Frequency	Once/24h	Multiple/24h
    Postictal deficit	No	Yes

  • Rx: Antipyretics; Diazepam if prolonged.
• Fever of Unknown Origin (FUO):
  • Definition: Fever >38.3°C for ≥3 weeks; no diagnosis after 1 week investigation.
  • Common causes: Infections (TB, typhoid), JIA, malignancy.
• Kawasaki Disease:
  • Criteria: Fever ≥5 days (the "Burn") + ≥4 of 📌 CRASH:
    • Conjunctivitis (bilateral)
    • Rash (polymorphous)
    • Adenopathy (cervical, ≥1.5cm)
    • Strawberry tongue/lip changes
    • Hand/foot changes (edema/erythema)
  • Rx: IVIG (2g/kg), Aspirin.

  ⭐ IVIG & Aspirin are crucial in Kawasaki Disease to prevent coronary artery aneurysms.

High‑Yield Points - ⚡ Biggest Takeaways

• Fever Without Source (FWS) in infants <3 months: Always investigate thoroughly (sepsis screen).
• Neonatal fever (<28 days): High risk of Serious Bacterial Infection (SBI); empirical antibiotics crucial.
• Febrile seizures: Commonest 6 months to 5 years; simple vs. complex differentiation is key.
• Kawasaki disease: Prolonged fever, rash, conjunctivitis, lymphadenopathy, mucosal changes; treat with IVIG and Aspirin.
• Urinary Tract Infection (UTI): Common cause of FWS, especially in girls; urine culture is gold standard.
• Roseola infantum (Exanthem subitum): High fever for 3-5 days, then rash appears as fever subsides.
• Occult bacteremia risk significantly ↓ post-vaccination era (Hib, Pneumococcal).