6.4 Common Pediatric Infections, Exanthems, & Fever of Unknown Origin
Key Takeaways
- Neonatal fever (age ≤ 28 days with temperature ≥ 38.0°C) is a medical emergency requiring full septic workup (blood, urine via catheter, lumbar puncture) and immediate IV empiric antibiotics (Ampicillin + Cefotaxime or Gentamicin).
- Classic pediatric exanthems are distinguished by key clinical features: Measles (Koplik spots, maculopapular rash starting at hairline spreading cephalocaudally), Scarlet fever (sandpaper rash, strawberry tongue, Pastia lines), Varicella (dewdrops on a rose petal in various stages of healing).
- Kawasaki Disease is diagnosed clinically by fever ≥ 5 days plus 4/5 criteria (conjunctivitis, mucositis/strawberry tongue, rash, cervical lymphadenopathy, extremity changes); immediate IVIG (2 g/kg) and high-dose aspirin are required to prevent coronary artery aneurysms.
- Acute Otitis Media (AOM) first-line treatment in Canada is high-dose Amoxicillin (80-90 mg/kg/day); watchful waiting for 48-72 hours is appropriate only for mild cases in children ≥ 6 months with reliable follow-up.
- Erythema Infectiosum (Fifth Disease / Parvovirus B19) presents with a "slapped cheek" rash followed by a reticulated lace-like trunk rash; it poses a grave risk of aplastic crisis in sickle cell patients and hydrops fetalis in pregnant women.
6.4 Common Pediatric Infections, Exanthems, & Fever of Unknown Origin
Evaluating fever and cutaneous eruptions in pediatric patients requires distinguishing benign self-limited viral exanthems from life-threatening systemic bacterial infections and vasculitides. Risk-stratified management of febrile infants and early recognition of Kawasaki disease are heavily tested MCCQE Part I domains.
Management of the Febrile Young Infant (0–90 Days)
Fever in infants is defined as a rectal temperature ≥ 38.0°C (100.4°F).
Neonatal Age 0 to 28 Days (High Risk)
Neonates possess immature immune systems and are at elevated risk for Invasive Bacterial Infections (IBI: bacteremia, meningitis, urinary tract infection).
- Pathogens: Group B Streptococcus (GBS), Escherichia coli (and other Gram-negative bacilli), Listeria monocytogenes, Herpes Simplex Virus (HSV).
- Mandatory Full Septic Workup:
- Complete blood count (CBC), differential, blood cultures.
- Catheterized urinalysis and urine culture.
- Lumbar Puncture (LP): CSF cell count, protein, glucose, Gram stain, bacterial culture, HSV PCR.
- Inflammatory markers: C-reactive protein (CRP) and Procalcitonin (PCT).
- Empiric Treatment: Immediate hospital admission and IV Ampicillin + Cefotaxime (or Ampicillin + Gentamicin). Add IV Acyclovir if HSV features present (maternal history, mucocutaneous vesicles, elevated transaminases, seizures).
Infants Aged 29 to 60 Days
Stratified using validated clinical decision rules (e.g., PECARN, Step-by-Step, or Aronson rules).
- Low-risk infants (reassuring labs, negative urinalysis, low procalcitonin) may undergo selective outpatient management with close 24-hour follow-up. High-risk infants require LP, hospital admission, and IV Ceftriaxone.
Pediatric Viral & Bacterial Exanthems
| Disease | Pathogen | Classic Clinical Features | Rash Description | Key Complications / Management |
|---|---|---|---|---|
| Measles (Rubeola) | Paramyxovirus | 3 Cs: Cough, Coryza, Conjunctivitis + Koplik spots (buccal mucosa) | Maculopapular, begins at hairline/face and spreads cephalocaudally | Subacute Sclerosing Panencephalitis (SSPE), pneumonia. Vitamin A therapy |
| Rubella (German Measles) | Rubella virus | Suboccipital & postauricular lymphadenopathy, Forchheimer spots | Erythematous maculopapular rash spreading face down; milder than measles | Congenital Rubella Syndrome (cataracts, PDA, sensorineural deafness) |
| Erythema Infectiosum (Fifth Disease) | Parvovirus B19 | Low-grade fever, prodrome | "Slapped cheek" facial erythema → reticulated lace-like trunk/extremity rash | Aplastic crisis in Sickle Cell/spherocytosis; Hydrops fetalis in pregnancy |
| Roseola Infantum (Exanthem Subitum) | HHV-6 (or HHV-7) | High fever (39-40°C) for 3-5 days that abates abruptly | Maculopapular rash appears AFTER fever breaks, starting on trunk | Leading cause of Febrile Seizures in infants aged 6-24 months |
| Varicella (Chickenpox) | Varicella-Zoster Virus (VZV) | Pruritic prodrome, fever | "Dewdrops on a rose petal" (vesicles on erythematous base) in all stages | Secondary bacterial skin infection (S. pyogenes necrotizing fasciitis), encephalitis |
| Hand-Foot-Mouth Disease | Coxsackievirus A16 / EV71 | Fever, painful oral stomatitis | Erythematous macules/vesicles on palms, soles, buttocks | Dehydration secondary to painful oral ulcers; self-limiting |
| Scarlet Fever | Streptococcus pyogenes (GAS) | Fever, exudative pharyngitis, Strawberry tongue | Sandpaper-texture rash, accentuation in flexural creases (Pastia lines) | Post-streptococcal glomerulonephritis, Acute Rheumatic Fever. Tx: Amoxicillin |
Kawasaki Disease (Mucocutaneous Lymph Node Syndrome)
Kawasaki disease is an acute self-limiting medium-vessel necrotizing vasculitis with a predilection for coronary arteries. It is the leading cause of acquired heart disease in children in developed countries.
Diagnostic Criteria
Fever lasting ≥ 5 days plus at least 4 of the 5 following clinical features (Mnemonic: CRASH and Burn [Fever]):
- Conjunctivitis: Bilateral non-exudative bulbar conjunctival injection.
- Rash: Polymorphous non-vesicular exanthem (maculopapular, scarlatiniform, or erythema multiforme-like).
- Adenopathy: Cervical lymphadenopathy (usually > 1.5 cm diameter, unilateral).
- Strawberries: Oral mucosal changes (red cracked lips, strawberry tongue, diffuse pharyngeal erythema).
- Hands & Feet: Extremity changes (acute erythema and edema of palms/soles; subungual desquamation in convalescent phase).
Incomplete Kawasaki Disease
Children with unexplained fever ≥ 5 days and 2 or 3 criteria with elevated inflammatory markers (CRP ≥ 30 mg/L, ESR ≥ 40 mm/h) warrant baseline Echocardiography to evaluate for coronary aneurysms.
Management Protocol (CPS Guidelines)
- Intravenous Immunoglobulin (IVIG): Single infusion of 2 g/kg administered over 10–12 hours within the first 10 days of fever onset. Significantly reduces coronary artery aneurysm risk from 25% down to < 4%.
- Acetylsalicylic Acid (ASA / Aspirin):
- High-dose ASA (80–100 mg/kg/day divided q6h) during acute febrile phase.
- Transition to low-dose ASA (3–5 mg/kg/day) once afebrile for 48 hours, continued for 6–8 weeks (or indefinitely if coronary aneurysms persist).
Exam Trap: Kawasaki disease is one of the very few pediatric indications for Aspirin despite Reye syndrome risk. Ensure VZV and influenza vaccinations are up to date in children on long-term ASA therapy.
Common Pediatric ENT Infections
Acute Otitis Media (AOM)
- Diagnosis: Requires acute onset, middle ear effusion (bulging tympanic membrane, loss of landmarks), AND signs of middle ear inflammation (intense erythema, otalgia).
- First-Line Antibiotic Therapy (Canada): High-dose Amoxicillin (80–90 mg/kg/day divided BID) for 10 days (<2 years) or 5 days (≥2 years).
- Watchful Waiting Option: CPS guidelines allow observation for 48–72 hours WITHOUT initial antibiotics only if: Age ≥ 6 months, mild otalgia, temperature < 39.0°C, non-severe presentation, AND reliable caregiver follow-up guaranteed.
Group A Streptococcal (GAS) Pharyngitis
- Diagnosis: Exudative pharyngitis in children > 3 years. Confirm with Rapid Antigen Detection Test (RADT) or throat swab culture.
- Treatment: First-line is Oral Penicillin V or Amoxicillin for 10 days. Primary objective is preventing Acute Rheumatic Fever.
A 18-day-old full-term infant is brought to the emergency department with a rectal temperature of 38.4°C. The infant is sleeping but easily rousable. Physical examination is unremarkable. Which of the following is the most appropriate mandatory management plan?
A 4-year-old child presents with a 6-day history of high fever (39.5°C). Examination reveals bilateral non-purulent conjunctival injection, dry cracked red lips with a bright red strawberry tongue, a polymorphous maculopapular trunk rash, and swollen tender erythema of both palms. CBC demonstrates thrombocytosis. What is the primary medical reason for initiating immediate intravenous immunoglobulin (IVIG) therapy?
A 9-month-old infant with no significant past medical history presents with a 4-day history of unremitting high fever (39.8°C). Today, the fever suddenly resolves completely, but a diffuse rose-pink maculopapular rash appears on the chest, abdomen, and back. The child is alert and drinking well. What is the most likely diagnosis?