What is the rash associated with strep throat in children and adults?

Scarlatiniform Rash (Scarlet Fever)

The rash associated with strep throat is a scarlatiniform rash (scarlet fever), which presents as a sandpaper-like, blanching, erythematous eruption caused by streptococcal pyrogenic exotoxins produced by certain strains of Group A beta-hemolytic streptococci (Streptococcus pyogenes). 1, 2

Clinical Characteristics of the Rash

The scarlatiniform rash has distinctive features that help identify it:

• Texture and appearance: The rash has a characteristic sandpaper-like quality with fine papules on an erythematous base 2
• Distribution: Typically begins on the trunk and spreads to the extremities, with increased intensity in skin folds (Pastia's lines) 1
• Timing: Appears within 1-2 days of pharyngitis onset, distinguishing it from late-onset rashes that can occur 7-20 days after treatment 3
• Associated features: The rash accompanies typical streptococcal pharyngitis symptoms including sudden onset sore throat, fever, tonsillopharyngeal erythema with or without exudates, and tender anterior cervical lymphadenopathy 4, 1, 2
• Additional oral findings: Patients often develop a "strawberry tongue" (red tongue with prominent papillae), beefy red swollen uvula, and palatal petechiae 1, 5

Epidemiology

• Age distribution: Scarlet fever primarily affects children aged 5-15 years, though it can occur in adults 4, 1
• Seasonality: Most common in winter and early spring in temperate climates 1
• Incidence: Only certain strains of Group A streptococci produce the pyrogenic exotoxins responsible for the rash, so not all strep throat cases develop scarlet fever 1, 2

Diagnostic Approach

Microbiological confirmation is essential because clinical features alone cannot reliably differentiate bacterial from viral pharyngitis, even when a rash is present. 1

• Rapid antigen detection test (RADT): A positive result is diagnostic for Group A streptococcal pharyngitis 4
• Throat culture: Remains the gold standard and should be performed as backup in children and adolescents with negative RADT results 4, 1
• Adults: Backup culture is generally not necessary due to lower incidence and rheumatic fever risk, though it can be considered 4

Important Differential Consideration

Arcanobacterium haemolyticum can produce a scarlet fever-like rash with pharyngitis, particularly in teenagers and young adults, though this is rarely recognized in the United States. 1, 2 This organism requires different diagnostic and treatment considerations.

Treatment Implications

When scarlet fever is confirmed, treatment follows standard Group A streptococcal pharyngitis protocols:

• First-line therapy: Penicillin V (250 mg four times daily or 500 mg twice daily in adults; 250 mg two or three times daily in children) for 10 days, or amoxicillin (50 mg/kg once daily, maximum 1000 mg) 4
• Penicillin allergy: First-generation cephalosporin, clindamycin, clarithromycin, or azithromycin 4
• Adjunctive therapy: Analgesics or antipyretics for symptom control; aspirin should not be used in children 4

Critical Pitfalls to Avoid

• Do not rely on clinical impression alone: The presence of a rash does not eliminate the need for microbiological confirmation, as viral exanthems can mimic scarlatiniform rash 4, 1
• Distinguish from late-onset rashes: Some patients develop maculopapular rashes 7-20 days after GAS pharyngitis treatment with amoxicillin, which are distinct from scarlet fever and may represent drug reactions 3
• Consider carrier state: Patients may be asymptomatic Group A streptococcal carriers (20% of school children) experiencing concurrent viral pharyngitis with viral exanthem 4, 1
• Recognize rare complications: Although uncommon, hepatitis can occur with scarlet fever and should be considered if patients develop dark urine or light-colored stools 5