Scarlet Fever Diagnosis: Clinical Features and Confirmatory Tests

Scarlet fever is a clinical diagnosis supported by laboratory confirmation.

Classic Triad

• Sore throat (streptococcal pharyngitis).
• Sandpaper rash: Fine, erythematous, blanchable; starts trunk → extremities; spares palms/soles; Pastia's lines in flexures.
• Strawberry tongue: White-coated initially → red, papillae prominent.

Other Features

• Fever, headache, abdominal pain, vomiting.
• Circumoral pallor.
• Desquamation (peeling) fingertips/toes in week 2–3.

Confirmatory Testing

• Rapid antigen detection test (RADT): Throat swab; specific, moderate sensitivity. Positive = treat.
• Throat culture: Gold standard; 24–48h. Done if RADT negative but clinical suspicion high.
• Anti-DNase B / ASO titers: Retrospective (rheumatic fever workup).

Treatment

Penicillin V (10 days) or amoxicillin; azithromycin/clindamycin for penicillin allergy. Prevents acute rheumatic fever, suppurative complications. Child non-contagious after 24h antibiotics.