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?
Perform catheterized urinalysis and discharge home with oral Amoxicillin
Perform blood culture, catheter urinalysis, and lumbar puncture; admit for IV Ampicillin and Cefotaxime
Administer single-dose IM Ceftriaxone in ED and re-evaluate in clinic in 24 hours
Order a chest X-ray and viral nasopharyngeal swab; hold antibiotics pending culture results
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?
To prevent the development of Post-Streptococcal Glomerulonephritis
To prevent acute retropharyngeal abscess formation
To reduce the risk of coronary artery aneurysm formation
To eradicate latent human herpesvirus-6 infection
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?
Roseola Infantum (Exanthem Subitum)
Measles (Rubeola)
Erythema Infectiosum (Fifth Disease)
Scarlet Fever
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