Percentage of Group A Streptococcal Infections That Develop Into Scarlet Fever
Approximately 10-20% of individuals with Group A Streptococcal (GAS) infections develop scarlet fever, with children aged 5-15 years being at highest risk. 1
Epidemiology of Group A Streptococcal Infections and Scarlet Fever
Group A Streptococcus (GAS) is a common bacterial pathogen that causes various clinical manifestations, with pharyngitis being the most frequent presentation. The development of scarlet fever depends on several factors:
- Age distribution: Children between 5-15 years have the highest incidence of GAS infections and subsequent scarlet fever 1
- Carrier status: Asymptomatic carriage rates vary by age:
- 10.9% in children aged 14 years or younger
- 2.3% in individuals aged 15-44 years
- 0.6% in those aged 45 years or older 1
Factors Affecting Scarlet Fever Development
The development of scarlet fever requires two specific conditions:
- Infection with a Group A Streptococcus strain that produces erythrogenic toxin
- Absence of antitoxin antibodies in the host
Not all GAS strains produce the erythrogenic toxin necessary for scarlet fever, which partly explains why only a subset of GAS infections progress to scarlet fever.
Clinical Presentation and Diagnosis
Scarlet fever presents with distinctive features beyond typical streptococcal pharyngitis:
- Sudden onset of sore throat
- Fever
- Headache
- Nausea, vomiting, and abdominal pain
- Characteristic sandpaper-like rash
- Strawberry tongue
- Patchy discrete exudate on tonsils
- Tender, enlarged anterior cervical nodes 1
The diagnosis of GAS infection should be confirmed through throat culture or rapid antigen detection testing (RADT), as clinical features alone cannot definitively diagnose GAS infection 1.
Transmission and Outbreaks
Scarlet fever can spread rapidly in school settings through direct contact between children. In documented outbreaks, attack rates can be significant:
- In a 2009 primary school outbreak in the UK, 45% of pupils (57 out of 126) developed scarlet fever over a 4-week period 2
- Transmission occurs primarily through direct contact between pupils, particularly among younger children
- Significant transmission also occurs between siblings 2
Complications and Prognosis
While scarlet fever is generally a mild illness with good prognosis, complications can occur:
- Suppurative complications: quinsy, acute otitis media, cervical lymphadenitis, mastoiditis, acute sinusitis
- Non-suppurative complications: acute rheumatic fever, acute glomerulonephritis 1
- Rare but serious complications include invasive GAS infection and streptococcal toxic shock syndrome 3
Most cases resolve without serious sequelae, with the median duration of school absence being approximately 3 days 2.
Treatment and Prevention
Appropriate antibiotic treatment is essential for preventing complications and reducing transmission:
- Penicillin V is the first-line treatment, administered for 10 days 1, 4
- For penicillin-allergic patients, erythromycin is recommended, though resistance rates can be high in some regions 5
- Patients are considered non-contagious after 24 hours of effective antibiotic therapy 4
Prevention Measures
- Hand hygiene
- Avoiding close contact with infected individuals
- Not sharing utensils or drinks
- Exclusion of infected children from school for 24 hours after initiating antibiotic treatment 4, 2
Key Takeaways
- The 10-20% development rate of scarlet fever from GAS infections highlights the importance of prompt diagnosis and treatment of streptococcal infections
- Children aged 5-15 years are at highest risk for both GAS infections and scarlet fever
- While generally mild, scarlet fever can occasionally lead to serious complications
- Appropriate antibiotic treatment reduces the risk of complications and limits transmission