## Post-Infectious Glomerulonephritis (PIGN) — Epidemiology **Key Point:** Group A Streptococcus (GAS) remains the most common infectious trigger of acute post-infectious glomerulonephritis in children, accounting for >90% of cases in endemic regions. ### Epidemiological Context **High-Yield:** PIGN typically follows a latency period of 1–3 weeks after GAS infection. Throat infection (pharyngitis) is more commonly associated with PIGN than skin infection, though both can trigger disease. ### Geographic Variation | Trigger Organism | Geographic Pattern | Clinical Context | | --- | --- | --- | | GAS pharyngitis | Temperate climates, endemic areas | Most common overall | | GAS skin infection (pyoderma) | Tropical/subtropical regions | Common in developing countries | | Staph aureus | Emerging in developed nations | Post-surgical, catheter-related | | Streptococcus pneumoniae | Rare | Historical significance only | ### Pathophysiology 1. **Antigen-antibody complex formation** — GAS antigens (M protein, hyaluronic acid) trigger immune response 2. **Immune complex deposition** — In situ formation at glomerular basement membrane 3. **Complement activation** — Classical pathway (C3 dominant on immunofluorescence) 4. **Glomerular inflammation** — Acute proliferative pattern on histology **Clinical Pearl:** The classic presentation includes hematuria (often cola-colored urine), proteinuria, hypertension, and edema appearing 1–3 weeks after GAS infection. **Mnemonic:** **PIGN-GAS** = Post-Infectious GN from Group A Streptococcus (the prototype organism). 
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