Which investigations and initial therapy should be performed in a school‑age child with fever, migratory arthritis, carditis, rash or chorea after a recent sore throat suggestive of acute rheumatic fever?

Investigations and Initial Therapy for Suspected Acute Rheumatic Fever

A school-age child presenting with fever, migratory arthritis, carditis, rash, or chorea after recent sore throat requires immediate laboratory confirmation of recent Group A streptococcal infection, echocardiography to detect carditis (including subclinical disease), and prompt initiation of penicillin therapy to eradicate residual streptococci, followed by continuous secondary prophylaxis to prevent recurrent attacks and progressive cardiac damage. 1, 2, 3

Essential Diagnostic Investigations

Laboratory Studies to Confirm Recent GAS Infection

• Obtain both anti-streptolysin O (ASO) and anti-DNase B antibody titers, as elevated or rising titers confirm recent Group A streptococcal infection in 99% of acute rheumatic fever cases 2, 3
• ASO titers peak 3-6 weeks after pharyngitis and remain elevated for several months, while anti-DNase B titers peak 6-8 weeks post-infection 2
• Throat culture should be performed even though it may be negative at presentation, since at least one-third of acute rheumatic fever cases result from inapparent streptococcal infections 3
• Elevated acute phase reactants (ESR and CRP) support the diagnosis and reflect systemic inflammatory response 2, 3

Cardiac Evaluation

• Echocardiography with Doppler must be performed immediately to fully characterize valvulitis, assess for pathological mitral and/or aortic regurgitation, and document baseline cardiac status 3, 4
• Echocardiography detects subclinical carditis in 41.3% of patients presenting with polyarthralgia alone and in 70% of patients with chorea, preventing both underdiagnosis and overdiagnosis 4
• ECG should be obtained to assess for prolonged PR interval, which serves as a minor Jones criterion 2, 3

Critical pitfall: Clinical examination alone misses significant carditis—in one multicenter study, 14% of patients with clinically diagnosed carditis had only functional murmurs, tachycardia, or anemia rather than true carditis, while echocardiography detected subclinical valvular disease in many patients without clinical findings 4

Application of Jones Criteria

The diagnosis requires two major manifestations OR one major plus two minor manifestations, accompanied by evidence of preceding GAS infection 3, 5:

Major criteria:

• Carditis (including subclinical valvulitis detected by echocardiography)
• Migratory polyarthritis (typically involving large joints, occurring 14-21 days post-pharyngitis)
• Sydenham chorea
• Erythema marginatum
• Subcutaneous nodules 1, 3

Minor criteria:

• Fever
• Arthralgia (cannot be counted if arthritis is used as major criterion)
• Elevated ESR or CRP
• Prolonged PR interval on ECG 3

Immediate Therapeutic Interventions

Eradication of Residual GAS

Administer a full therapeutic course of penicillin immediately, even if throat culture is negative at diagnosis, as this eradicates any residual streptococci 1, 2, 3:

• Penicillin V: 250 mg 2-3 times daily for children <27 kg; 500 mg 2-3 times daily for children ≥27 kg, for 10 days 2, 3
• Amoxicillin: 50 mg/kg once daily (maximum 1 g) for 10 days 3
• Benzathine penicillin G (IM): Single dose of 600,000 units for patients <27 kg; 1,200,000 units for patients ≥27 kg 2, 3

For penicillin-allergic patients:

• Non-anaphylactic allergy: First-generation cephalosporin for 10 days 2, 3
• Anaphylactic/immediate hypersensitivity: Clindamycin 20 mg/kg/day divided 3 times daily (maximum 1.8 g/day) for 10 days, OR azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days 2, 3

Anti-Inflammatory Therapy

• Acetylsalicylic acid (aspirin) for arthritis and mild carditis—the arthritis of rheumatic fever responds rapidly to aspirin, unlike post-streptococcal reactive arthritis 1
• Corticosteroids should be considered for severe carditis with significant valvular involvement 3

Mandatory Secondary Prophylaxis

Continuous antimicrobial prophylaxis must be initiated immediately upon diagnosis to prevent recurrent attacks, as recurrent rheumatic fever occurs in 18.7% of patients despite prophylaxis recommendations and can worsen cardiac damage with each episode 1, 3, 6:

• Benzathine penicillin G 1,200,000 units IM every 4 weeks (600,000 units for patients <27 kg) is the gold standard, being approximately 10 times more effective than oral antibiotics 2

Duration of prophylaxis depends on cardiac involvement 1:

• No carditis: 5 years or until age 21 (whichever is longer)
• Carditis without residual valvular disease: 10 years or until age 21 (whichever is longer)
• Carditis with residual valvular disease: 10 years or until age 40 (whichever is longer), sometimes lifelong

Household Contact Management

Obtain throat swab specimens from ALL household contacts and treat positive contacts regardless of symptoms, as this prevents transmission and potential rheumatic fever development in genetically susceptible family members 1, 2, 3

Key Diagnostic Challenges to Recognize

• Approximately 15% of school-age children are asymptomatic GAS carriers, making it difficult to distinguish true infection from carriage with concurrent viral pharyngitis 3
• Significant overlap exists with Lyme disease, serum sickness, drug reactions, and post-streptococcal reactive arthritis, requiring careful clinical judgment 5
• Post-streptococcal reactive arthritis (PSRA) differs from rheumatic fever: it occurs 10 days (not 14-21 days) after pharyngitis, does not respond readily to aspirin, is cumulative and persistent (not migratory and transient), and can involve small joints or axial skeleton 1
• Patients with PSRA should be observed carefully for several months for clinical evidence of carditis and may receive secondary prophylaxis for up to 1 year, though its effectiveness is not well established 1