Scarlet Fever

Scarlet fever is a clinical syndrome caused by Group A Streptococcus (GAS, Streptococcus pyogenes) that produces erythrogenic (pyrogenic) exotoxins (SpeA, SpeB, SpeC). These superantigen toxins activate large numbers of T cells (up to 20% of the T cell population, compared to <0.01% by conventional antigens), causing massive cytokine release that produces the characteristic widespread erythematous rash. Scarlet fever most commonly occurs as a complication of streptococcal pharyngitis in children aged 5-15 years. The rash appears 12-48 hours after pharyngitis onset as a diffuse, fine, sandpaper-textured erythematous eruption starting on the trunk and spreading to extremities, sparing the palms and soles. Pastia lines (linear petechiae in skin folds, especially antecubital fossae and inguinal creases) and a 'strawberry tongue' (white-coated initially, then red with prominent papillae) are characteristic. The face shows flushing with circumoral pallor. Treatment with penicillin or amoxicillin eradicates GAS and prevents serious complications, particularly acute rheumatic fever (ARF, which occurs 2-4 weeks after untreated streptococcal pharyngitis) and post-streptococcal glomerulonephritis (PSGN, which occurs 1-3 weeks after pharyngeal or skin GAS infection).