Scarlet fever

Definition
Scarlet fever is an acute infectious disease caused by Group A beta-haemolytic Streptococcus (Streptococcus pyogenes), characterised by pharyngitis, a fine red rash, and desquamation. It primarily affects children but can occur at any age.

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Causes

• Caused by strains of S. pyogenes producing erythrogenic (pyrogenic) exotoxins

• Spread via respiratory droplets, direct contact, or shared items

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Risk Factors

• Children aged 5–15 years

• Crowded environments (schools, nurseries)

• Close contact with infected individuals

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Pathophysiology

• Streptococcal exotoxins act as superantigens, triggering widespread immune activation and capillary dilation → rash and systemic symptoms

• Often follows streptococcal pharyngitis or, less commonly, skin infection (scarletina)

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Clinical Features

Early Symptoms (1–2 days after infection)

• Fever (>38.3°C)

• Sore throat, difficulty swallowing

• Headache, malaise

• Abdominal pain, nausea/vomiting (especially in children)

Characteristic Signs

• Rash: Fine, sandpaper-like erythema starting on the trunk, spreading to extremities; blanches with pressure; accentuated in skin folds (Pastia’s lines)

• Facial flushing with circumoral pallor

• Strawberry tongue: initially white-coated with red papillae, later becoming bright red

• Desquamation: peeling of skin (fingers, toes) during recovery phase

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Diagnosis

• Clinical features plus confirmation with:

  • Throat swab for Group A Streptococcus (rapid antigen test or culture)

  • Blood tests: elevated WBC, ESR, CRP

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Treatment

First-Line Antibiotics (eradicates bacteria, prevents complications)

• Phenoxymethylpenicillin (Penicillin V):

  • Adults: 500 mg orally every 6 hours for 10 days

  • Children: 250 mg orally every 6 hours for 10 days (or weight-based 12.5 mg/kg/dose q6h, max 500 mg/dose)

• Alternative (penicillin allergy): Azithromycin 500 mg orally on day 1, then 250 mg once daily on days 2–5

Supportive Measures

• Paracetamol or ibuprofen for fever and pain

• Adequate hydration

• Soft diet if throat pain is severe

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Complications

• Suppurative: otitis media, sinusitis, peritonsillar abscess

• Non-suppurative: acute rheumatic fever, post-streptococcal glomerulonephritis

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Prevention

• Early treatment of streptococcal pharyngitis

• Avoid sharing utensils or drinks during infection

• Exclude infected children from school for at least 24 hours after starting antibiotics

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Quick-Reference Clinical Chart — Scarlet Fever

Feature	Details
Definition	Streptococcal infection with toxin-mediated rash and systemic symptoms
Cause	Streptococcus pyogenes (Group A beta-haemolytic)
Transmission	Respiratory droplets, direct contact
Incubation	1–5 days
Key Symptoms	Fever, sore throat, rash, strawberry tongue
Key Signs	Sandpaper rash, Pastia’s lines, circumoral pallor
Diagnosis	Clinical + throat swab
First-Line Treatment	Penicillin V 500 mg q6h for 10 days (adults)
Alternative	Azithromycin (if penicillin allergy)
Complications	Rheumatic fever, glomerulonephritis, otitis media
Prognosis	Excellent with early treatment