Scarlet Fever

Definition & Causative Agent

• Primarily a childhood disease, most common in winter and early spring
• Up to 10% of childhood Group A streptococcal pharyngitis cases progress to scarlet fever

Pathogenesis

• SPEA, SPEB, SPEC — streptococcal pyrogenic exotoxins
• Most modern isolates express the less virulent SPEB and SPEC rather than SPEA, explaining reduced severity compared to historical epidemics
• The mechanism involves a combination of delayed-type hypersensitivity and superantigen-mediated immune activation
• SPEA shares homology with collagen, potentially underpinning rare autoimmune sequelae (rheumatic fever, renal failure)

Clinical Features

Prodrome (12 hours – 5 days post-exposure)

• High fever
• Pharyngitis / sore throat
• Headache
• Vomiting
• Abdominal pain

Exanthem (appears 1–2 days after onset)

Sandpaper-like rash spreading over the trunk

• Begins on the neck, axillae, and groin, spreads to trunk and extremities
• Spares palms and soles
• Fine punctate, 1–2 mm papules with a characteristic sandpaper texture
• Erythema blanches with pressure
• Mildly pruritic but usually not painful
• Pastia lines: linear petechial streaks in antecubital and axillary folds (increased capillary fragility)
• Flushed face with circumoral pallor
• Rash fades at 3–4 days → brawny desquamation beginning on the face, then palms/fingers/soles (~1 week later, lasting up to 1 month)

Enanthem (oral findings)

A: Sandpaper erythema; B: Close-up texture; C: "Strawberry" red tongue; D: Post-streptococcal desquamation of hands

• Tonsils and pharynx: red, edematous, with yellow/grey/white exudate
• Tender anterior cervical lymphadenopathy
• Forchheimer spots: petechiae and red macules on the soft palate and uvula
• White strawberry tongue (days 1–2): white coating with prominent red papillae projecting through
• Red strawberry tongue (after day 2–4): coating desquamates → bright red tongue with prominent papillae

Diagnosis

• Primarily clinical based on the characteristic signs
• Confirmed by rapid streptococcal antigen test or throat culture (Group A β-hemolytic streptococci)
• Usually benign course; morbidity signals suppurative complications

Complications

Suppurative

• Streptococcal adenitis
• Tonsillitis
• Otitis media
• Respiratory tract infection

Non-suppurative (late)

• Acute rheumatic fever (antibiotic treatment reduces this risk)
• Post-streptococcal glomerulonephritis (antibiotic effect on this is less clear)

Erythema marginatum may be seen in ~10% of cases — annular erythematous lesions that can recur over days to weeks.

Treatment

• Fever usually resolves within 12–24 hours of antibiotic initiation
• Recurrences are common

Staphylococcal Scarlet Fever (Scarlatiniform Erythroderma)

• Nidus is usually skin (furuncles, carbuncles, abscesses) — no pharyngitis
• Same generalized sandpaper-texture erythroderma, but more tender
• Thick desquamation follows over ~1 week; no bullae (unlike SSSS)
• No risk of rheumatic fever or glomerulonephritis
• Suspect staphylococcal etiology when rash is present without pharyngitis — look for a skin nidus to culture

Differential Diagnosis