Scarlet fever
Essentials
- Acute toxin‑mediated illness caused by Group A Streptococcus (GAS; usually Streptococcus pyogenes). Most common in preschool children (peak ~2-6 years).
- Typical course: prodrome of fever, malaise and sore throat followed 12-48 hours later by a diffuse “sandpaper” erythematous rash, flushed cheeks with perioral pallor, and a strawberry tongue. Desquamation of fingertips/toes occurs in convalescence (UKHSA).
- Diagnosis is clinical; start antibiotics promptly - do not wait for throat swab results (UKHSA, NICE NG84).
- First‑line therapy: phenoxymethylpenicillin (penicillin V) four times daily for 10 days. Children can return to school 24 hours after starting appropriate antibiotics. Notify the local health protection team - scarlet fever is notifiable (UKHSA).
Epidemiology and pathogenesis
- Caused by erythrogenic (pyrogenic) exotoxins produced by certain phage‑encoded strains of GAS. Presentation reflects both local throat infection (pharyngitis/tonsillitis) and systemic toxin effects on skin and mucous membranes.
- Incubation period is typically 2-4 days (commonly quoted up to 5 days).
- Peak incidence is in children aged 2-6 years (peak ~4 years).
Clinical features
- Prodrome: sudden fever, malaise, headache and sore throat.
- Oral signs: “strawberry” tongue - initially coated white with prominent papillae, later showing red/raw papillae. Pharyngeal erythema and tonsillar exudates may be present.
- Rash: diffuse, fine punctate erythema (“pin‑head”) producing a rough, sandpaper texture. Classically appears first on the trunk, then spreads to the neck, groins and...