Scarlet Fever: The Strep Throat Rash—Presentation, Diagnosis, and Treatment

Scarlet fever (scarlatina) is a toxin-mediated manifestation of Group A Streptococcal infection, characterized by a distinctive rash. It occurs in about 10% of untreated strep throat cases, predominantly in children 5–15 years old.

Pathogenesis

• Streptococcal pyrogenic exotoxins (SpeA, SpeC, SpeG) act as superantigens → massive T-cell activation → cytokine storm → rash, fever, strawberry tongue.
• Same strains cause strep throat; toxin production varies by phage-encoded genes.

Clinical Features

• Rash: Diffuse erythematous, fine papules (“sandpaper” texture); begins on neck/chest/axillae → spreads centrifugally; spares palms/soles initially.
• Pastia's lines: Linear petechiae in antecubital, axillary, inguinal folds (capillary fragility).
• Facial flushing with circumoral pallor.
• Strawberry tongue: White coating (days 1–2) → red, prominent papillae (days 3–5).
• Desquamation: Fine peeling on fingertips, toes, trunk (weeks 2–3).
• Accompanying: Fever, sore throat, exudates, adenopathy, headache, nausea, abdominal pain.

Diagnosis

• Clinical: Rash + strep throat signs.
• Confirmatory: Positive RADT or throat culture for GAS.
• Differential: Kawasaki (prolonged fever, conjunctivitis, no exudate), measles (cough/coryza/conjunctivitis, Koplik spots), drug eruption, toxic shock, viral exanthems.

Treatment

• Identical to strep throat: Penicillin/amoxicillin × 10 days (or alternatives for allergy).
• Antibiotics reduce transmission, suppurative complications, and may attenuate rheumatic fever risk (though ARF prevention window is 9 days from onset).
• Supportive: Antipyretics, hydration, emollients for desquamation.

Complications

• Same as strep throat: Peritonsillar abscess, lymphadenitis, ARF, PSGN.
• Rare: Toxic shock syndrome (TSLS), septic arthritis, osteomyelitis.

Infection Control

• Exclude from school/childcare until ≥24 hours on antibiotics + afebrile.
• Household contacts: Monitor for symptoms; test if symptomatic.
• No prophylaxis for asymptomatic contacts.

Key Message

Scarlet fever is strep throat with a rash—caused by the same bacterium, treated with the same antibiotics. Prompt treatment prevents complications and stops spread. The rash itself is not dangerous; the untreated infection is.