Scarlet Fever

Risk factors

• School and household exposure to streptococcal pharyngitis
• Age 5-15 years
• Winter-spring season
• Crowded living

Pathophysiology

Streptococcus pyogenes producing erythrogenic exotoxins releases them systemically; the toxins act as superantigens, causing widespread T-cell activation and the characteristic erythema and tongue papillary changes. The diffuse rash reflects toxin-mediated vasodilation, not direct infection of the skin.

Clinical presentation

Differential diagnosis

• Kawasaki disease — ≥5 days fever, conjunctivitis, extremity changes, polymorphous rash; risk of coronary aneurysms
• Staphylococcal scarlet fever / toxic shock — Toxin-mediated diffuse erythroderma with hypotension; staphylococcal source rather than pharyngeal
• Drug eruption — Recent new medication; not associated with pharyngitis
• Measles — Three Cs, Koplik spots, cephalocaudal maculopapular rash
• Viral exanthems (EBV, adenovirus) — Often less brisk desquamation, lack strawberry tongue

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Pharyngitis<br/>+ sandpaper rash<br/>+ strawberry tongue] --> B[Rapid antigen test<br/>± throat culture]
  B --> C{Positive?}
  C -->|Yes| D[Penicillin V<br/>or amoxicillin x 10 d]
  C -->|No, child or teen| E[Backup throat culture<br/>treat only if positive]
  C -->|No, adult| J[Negative RADT sufficient<br/>no backup culture]
  E -->|Culture positive| D
  D --> F[Return to school<br/>after 24 h Abx + afebrile]
  D --> G{Monitor for sequelae}
  G --> H[Rheumatic fever<br/>preventable]
  G --> I[PSGN<br/>NOT preventable]

Treatment

Complications

• Suppurative: peritonsillar abscess, retropharyngeal abscess, otitis media, cervical lymphadenitis, sinusitis
• Non-suppurative (immune-mediated): acute rheumatic fever (preventable by adequate antibiotic treatment), post-streptococcal glomerulonephritis (NOT prevented by treatment), pediatric autoimmune neuropsychiatric disorders associated with strep (PANDAS)
• Streptococcal toxic shock syndrome with invasive strains
• Desquamation of skin in fingertips and toes (cosmetic, self-limited)

PANCE pearls

• Strawberry tongue + sandpaper rash + sore throat = scarlet fever; confirm with RADT/culture.
• Adequate penicillin/amoxicillin treatment prevents rheumatic fever but does NOT prevent post-streptococcal glomerulonephritis.
• Desquamation of fingertips and toes 1-2 weeks later is a clue when the rash itself has been forgotten.
• Penicillin remains first-line because Streptococcus pyogenes has never developed clinical penicillin resistance.
• Consider Kawasaki disease in a child with ≥5 days fever, conjunctivitis, and mucosal changes who fails to clear with antibiotics.

References

• IDSA 2012 — IDSA Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis (Shulman et al., Clin Infect Dis 2012)
• AAP Red Book — American Academy of Pediatrics Red Book — Group A Streptococcal Infections
• AHA 2009 — AHA Scientific Statement on Prevention of Rheumatic Fever and Diagnosis and Treatment of Acute Streptococcal Pharyngitis (Gerber et al., Circulation 2009)