What is the difference between scarlet fever and rheumatic fever?

Scarlet Fever vs. Rheumatic Fever: Key Distinctions

Scarlet fever is an acute infection caused by Group A Streptococcus (GAS) that occurs during the active bacterial infection, while rheumatic fever is a delayed autoimmune complication that develops 14-21 days after a GAS infection as a non-suppurative sequela. 1, 2, 3

Fundamental Differences

Timing and Pathophysiology

• Scarlet fever occurs during the acute phase of GAS pharyngitis, characterized by the presence of active bacterial infection with streptococcal toxin production 2
• Rheumatic fever develops as a delayed autoimmune phenomenon 14-21 days after the initial GAS pharyngitis, impetigo, or scarlet fever, occurring after a symptom-free interval 1, 3
• The key distinction is that scarlet fever represents the infection itself, while rheumatic fever represents an autoimmune response to that infection 3

Clinical Presentation

Scarlet fever features:

• Fever with pharyngitis or tonsillitis with exudates 4, 5
• Characteristic sandpaper-like rash caused by streptococcal toxin 2
• Symptoms occur during active GAS infection 2
• Diagnosis is clinical, supported by positive throat culture or rapid antigen detection test 4

Rheumatic fever features:

• Diagnosed using Jones criteria: requires two major criteria OR one major and two minor criteria, plus evidence of preceding GAS infection 1
• Major criteria: carditis, polyarthritis, chorea, subcutaneous nodules, erythema marginatum 1
• Minor criteria: previous rheumatic fever/rheumatic heart disease, arthralgia, fever, elevated inflammatory markers (ESR, CRP, leukocytosis), prolonged PR interval 1
• The arthritis is migratory, transient, involves large joints, and responds rapidly to aspirin 1

Critical Clinical Implications

Morbidity and Mortality Differences

• Scarlet fever is now relatively benign with low mortality when treated appropriately 6, 2
• Rheumatic fever carries significant risk of permanent cardiac damage, with potential for severe rheumatic heart disease and lifelong disability 1, 3
• Rheumatic fever can cause valvular heart disease that may require lifelong prophylaxis and can worsen with recurrent attacks 1

Treatment Approaches

For scarlet fever:

• Immediate antibiotic therapy: penicillin V 250 mg twice daily for children, 500 mg 2-3 times daily for adolescents/adults for 10 days 4
• Patient becomes non-contagious after 24 hours of antibiotics 4
• Primary goal is to treat the active infection and prevent rheumatic fever as a complication 4, 5

For rheumatic fever:

• Full therapeutic course of penicillin to eradicate residual GAS, even if throat culture is negative 4
• Continuous antimicrobial prophylaxis is mandatory to prevent recurrences: benzathine penicillin G 1.2 million units IM every 4 weeks 4
• Duration of prophylaxis depends on cardiac involvement:
  • With carditis and residual heart disease: 10 years or until age 40 (whichever is longer), sometimes lifelong 1, 4
  • With carditis but no residual disease: 10 years or until age 21 (whichever is longer) 1, 4
  • Without carditis: 5 years or until age 21 (whichever is longer) 1

Critical Pitfalls to Avoid

The Prevention Paradox

• At least one-third of rheumatic fever cases result from asymptomatic GAS infections, meaning patients never had recognized scarlet fever or pharyngitis 4
• Even when scarlet fever is treated optimally with appropriate antibiotics, rheumatic fever can still occur in susceptible individuals 4, 5
• This explains why rheumatic fever cannot be completely prevented by treating scarlet fever alone 4

Diagnostic Challenges

• The absence of supporting evidence of preceding streptococcal infection should make rheumatic fever diagnosis doubtful, except in Sydenham chorea or low-grade carditis discovered after a long latent period 1
• Untreated or inadequately treated GAS pharyngitis (including scarlet fever) carries approximately 3% risk of rheumatic fever during epidemics 5
• Recurrent rheumatic fever can occur even with appropriate treatment of GAS infections, necessitating continuous rather than episodic prophylaxis 4

Post-Streptococcal Reactive Arthritis (PSRA)

• PSRA is a distinct entity that can be confused with rheumatic fever 1, 7
• PSRA occurs 10 days after GAS pharyngitis (vs. 14-21 days for rheumatic fever), has persistent non-migratory arthritis affecting large and small joints, and does not respond readily to aspirin 1
• Some PSRA patients have developed valvular heart disease, so they should be observed carefully for several months and may receive prophylaxis for up to 1 year 1