Scarlet Fever Summary

Definition

  • Notifiable infectious disease
  • Group A Streptococcus (GAS)
  • Exotoxin/superantigen mediated
  • Most common: children 2-8 years

Transmission

  • Highly contagious
  • Aerosol/direct contact
  • Incubation: 2-3 days
  • Infectious 2-3 weeks untreated

Clinical Features

  • Sore throat, fever >38.3°C
  • Sandpaper-like rash
  • Strawberry tongue
  • Circumoral pallor

Management

  • Notify health protection
  • Penicillin V 10 days
  • Exclusion ≥24h post-antibiotics
  • Supportive care

Complications

  • Early: Otitis, abscesses
  • Late: Rheumatic fever
  • Invasive: Sepsis, TSS

High-Risk Groups

  • Extremes of age
  • Immunocompromised
  • Diabetes, malignancy
  • Substance use

Scarlet Fever

Notifiable infectious disease caused by group A streptococcus

Introduction

Scarlet fever is a notifiable infectious disease caused by the bacterium Streptococcus pyogenes, also known as group A streptococcus (GAS). When GAS cause infection, the primary site is usually the throat resulting in pharyngitis. The rash and fever associated with scarlet fever are due to exotoxin or superantigen release by the bacteria.

Age Distribution

Scarlet fever can occur at any age but is most common in children between 2–8 years of age (median age 4 years).

Transmission

Bacterial Colonization

GAS bacteria can colonise the throat or skin. Asymptomatic pharyngeal carriage of S. pyogenes occurs in 3–26% of healthy children. The incubation period is usually 2–3 days but can range from 1–6 days.

Transmission Routes

  • Aerosol transmission (coughing, sneezing)
  • Direct contact with contaminated surfaces
  • Contact with infected saliva or mucus

Epidemiology

  • Highly contagious
  • Outbreaks in nurseries, schools, institutions
  • Infectious for 2–3 weeks without treatment

Clinical Features

Initial Symptoms

  • Sore throat
  • Fever (typically >38.3°C)
  • Headache, fatigue
  • Nausea and vomiting

Rash Characteristics

  • Develops 12–48 hours after initial symptoms
  • Starts on trunk, spreads to body and flexures
  • Red, generalized, pinpoint (punctate)
  • Rough, sandpaper-like texture
  • Accentuated in skin folds (Pastia's lines)
  • Palms and soles typically spared
  • Skin may peel after rash resolves

Examination Findings

Oral Findings

  • Strawberry tongue (white coat → beefy red)
  • Pharyngitis
  • Petechiae on hard/soft palate (Forchheimer spots)

Other Findings

  • Cervical lymphadenopathy
  • Flushed face with circumoral pallor

Differential Diagnosis

Viral Infections

  • Rubella
  • Parvovirus B19 infection
  • Measles
  • Roseola infantum (herpesvirus type 6)
  • Enterovirus and adenovirus infections
  • HIV, cytomegalovirus, toxoplasmosis
  • Echovirus, Coxsackievirus, viral hepatitis
  • Tropical viruses (Dengue fever)

Other Conditions

  • Kawasaki disease
  • Staphylococcal toxic shock syndrome (TSS)
  • Brucellosis, syphilis
  • Mononucleosis reaction to amoxicillin
  • Adverse drug reactions

Investigations

Routine Testing

Throat swabs and blood tests are not routinely indicated for the diagnosis of scarlet fever.

When to Consider Throat Swab

Indications for Testing

  • Uncertainty about clinical diagnosis
  • Suspected outbreak (consult health protection team)
  • True penicillin allergy (for susceptibility testing)
  • Case in contact with vulnerable high-risk people

Serological Testing

Measurement of serum antistreptolysin O (ASO) antibody titres are not useful in acute infection, but may be helpful in the diagnosis of post-infection complications such as acute rheumatic fever or glomerulonephritis.

Management

Notification Requirement

Notify the local health protection team promptly within 3 days by completing a notification form if a diagnosis of scarlet fever is suspected.

Hospital Admission

  • Consider if severe symptoms
  • Suspected serious/life-threatening complications
  • High risk of developing complications

Antibiotic Treatment

  • Prescribe regardless of severity if not admitted
  • First-line: phenoxymethylpenicillin (penicillin V)
  • Four times daily for 10 days

Patient Advice

Self-Care Measures

  • Paracetamol or ibuprofen for symptom relief
  • Adequate rest
  • Adequate fluid intake

Infection Control

  • Exclusion for ≥24 hours after starting antibiotics
  • Effective and frequent handwashing
  • Avoid sharing utensils and towels
  • Dispose of tissues promptly
  • Avoid contact with high-risk people

Complications

Suppurative Complications

Due to local spread, occur early in infection:

  • Otitis media
  • Throat infection and abscess:
    • Peritonsillar cellulitis
    • Peritonsillar abscess
    • Retropharyngeal abscess
  • Acute sinusitis and mastoiditis

Non-Suppurative Complications

Immune-mediated, occur later, especially if untreated:

  • Acute rheumatic fever:
    • Immunologically-mediated response
    • Carditis and endocarditis
    • Valvular heart disease
    • Reactive arthritis
  • Acute post-streptococcal glomerulonephritis:
    • Occurs 2+ weeks after initial infection
    • Haematuria, reduced urine output
    • Peripheral oedema, proteinuria
    • Hypertension

Invasive Group A Streptococcal (iGAS) Infections

Life-Threatening Complications

  • Streptococcal pneumonia
  • Meningitis and cerebral abscess
  • Endocarditis, septic arthritis, liver abscess
  • Cellulitis, necrotising fasciitis
  • Streptococcal toxic shock syndrome
  • Sepsis
  • Risk of death

High-Risk Groups for Complications

Demographic Factors

  • Extremes of age (very young and old)
  • Postpartum women

Medical Conditions

  • Immunocompromised or immunosuppressed
  • Skin breakdown
  • Diabetes mellitus
  • Underlying malignancy
  • Concurrent chickenpox or influenza

Lifestyle Factors

  • People who inject drugs
  • Alcohol dependent