Poststreptococcal glomerulonephritis typically occurs after infection with which organism?

• A. Staphylococcus aureus
• B. Streptococcus pyogenes
• C. Streptococcus pneumoniae
• D. Enterococcus faecalis

Answer: (B)

Poststreptococcal glomerulonephritis is driven by immune complex deposition after infection with Streptococcus pyogenes, the group A beta-hemolytic streptococcus. Following a pharyngeal infection or impetigo, antibodies against streptococcal antigens (such as streptolysin O and DNase B) form circulating immune complexes that settle in the glomeruli. This activates complement and triggers inflammation, leading to a nephritic picture with hematuria (often with red cell casts), mild to moderate proteinuria, hypertension, and edema. The usual delay is about 1–3 weeks after a throat infection and 3–6 weeks after a skin infection. Thus, the organism most classically associated with this condition is Streptococcus pyogenes.