A patient with a sore throat develops a kidney biopsy two weeks later. Which organism would be isolated?

A patient with a sore throat develops a kidney biopsy two weeks later. Which organism would be isolated?

• A. Neisseria meningitidis
• B. Streptococcus pyogenes
• C. Haemophilus influenzae
• D. None of the above

Answer: (D)

Postinfectious glomerulonephritis after a sore throat is driven by immune complexes formed in response to a nephritogenic streptococcal infection, not by a current bacterial invasion of the kidney. By about two weeks after the throat infection, the organism itself is usually cleared from the kidneys; the damage seen in the kidney is due to deposition of antibodies and complement in the glomeruli, not ongoing infection. On biopsy you’d expect immune complex–mediated changes (granular IgG/IgM and C3 deposits with hypercellular glomeruli and, sometimes, subepithelial “humps” on EM), along with low serum C3. Because there isn’t a live organism present in the kidney at this stage, no organism would be isolated from the biopsy. While a prior Streptococcus pyogenes infection can be the trigger, the biopsy itself does not yield an active bacterial isolate, so none of the listed organisms would be isolated.

Postinfectious glomerulonephritis after a sore throat is driven by immune complexes formed in response to a nephritogenic streptococcal infection, not by a current bacterial invasion of the kidney. By about two weeks after the throat infection, the organism itself is usually cleared from the kidneys; the damage seen in the kidney is due to deposition of antibodies and complement in the glomeruli, not ongoing infection. On biopsy you’d expect immune complex–mediated changes (granular IgG/IgM and C3 deposits with hypercellular glomeruli and, sometimes, subepithelial “humps” on EM), along with low serum C3. Because there isn’t a live organism present in the kidney at this stage, no organism would be isolated from the biopsy. While a prior Streptococcus pyogenes infection can be the trigger, the biopsy itself does not yield an active bacterial isolate, so none of the listed organisms would be isolated.