A 28-year-old woman presents with acute pharyngitis, fever, and exudative tonsils. Culture on blood agar yields β-hemolytic colonies that are bacitracin-sensitive. What is the most common complication of untreated Streptococcus pyogenes pharyngitis in the Indian subcontinent?

Explanation

## Most Common Complication of S. pyogenes Pharyngitis **Key Point:** Acute rheumatic fever (ARF) is the most common and clinically significant sequela of untreated or inadequately treated S. pyogenes pharyngitis, particularly in resource-limited settings and the Indian subcontinent where rheumatic heart disease remains endemic. ### Epidemiology & Pathogenesis **High-Yield:** ARF develops in 3–5% of untreated S. pyogenes pharyngitis cases, typically 2–3 weeks after the acute infection. The mechanism involves molecular mimicry: streptococcal M protein shares epitopes with cardiac myosin, tropomyosin, and other cardiac proteins, triggering cross-reactive autoimmune damage. ### Why ARF is Most Common | Complication | Frequency | Timing | Mechanism | | --- | --- | --- | --- | | **Acute Rheumatic Fever** | 3–5% of untreated pharyngitis | 2–3 weeks post-infection | Molecular mimicry; T-cell mediated autoimmunity | | Post-streptococcal GN | 10% of untreated pharyngitis | 1–2 weeks post-infection | Immune complex deposition | | Scarlet fever | Occurs during acute infection | Concurrent with pharyngitis | Erythrogenic toxin production | | Acute epiglottitis | Rare with S. pyogenes | Days of acute infection | Direct invasion (not a typical sequela) | **Clinical Pearl:** In India and other developing nations, ARF is the leading cause of acquired heart disease in children and young adults. Secondary prophylaxis with monthly IM penicillin G is mandatory after the first episode to prevent recurrent attacks and progressive cardiac damage. **Mnemonic — Major Criteria of ARF (Jones Criteria):** **JONES** - **J**oints (migratory polyarthritis) - **O**rganomegaly (carditis with valvulitis) - **N**odules (subcutaneous) - **E**rythema (marginatum) - **S**ydenham chorea ### Distinction from Post-Streptococcal Glomerulonephritis While post-streptococcal glomerulonephritis (PSGN) is also common (10% of untreated infections), it is: - More frequent after *skin* infections (impetigo) than pharyngitis - Usually self-limited with good prognosis - Less likely to cause chronic sequelae compared to ARF In contrast, ARF carries the risk of permanent cardiac valve damage and is the primary reason for aggressive treatment and prophylaxis of S. pyogenes infections in endemic regions. [cite:Harrison 21e Ch 297]