A 16-year-old girl develops acute glomerulonephritis two weeks after a skin infection with Group A Streptococcus. Her throat culture is negative. ASO titres are low but anti-DNase B titres are elevated. What does this pattern indicate?
- A The GAS infection was cutaneous; ASO is neutralised by skin lipids and anti-DNase B is the preferred marker for impetigo-associated PSGN ✓
- B The GAS infection was pharyngeal; ASO is unreliable for skin infections
- C The elevated anti-DNase B indicates concurrent Staphylococcal infection
- D False positive anti-DNase B from cross-reacting Group B Streptococcus
Correct answer: A. The GAS infection was cutaneous; ASO is neutralised by skin lipids and anti-DNase B is the preferred marker for impetigo-associated PSGN
Explanation
Post-streptococcal glomerulonephritis (PSGN) following skin infection (impetigo) is characterised by low or absent ASO titres because skin lipids neutralise streptolysin O, preventing antibody formation. Anti-DNase B (anti-deoxyribonuclease B) is the most reliable serological marker for skin-origin GAS infection and PSGN after pyoderma. The distinction is clinically important as anti-DNase B is the appropriate test to confirm preceding GAS cutaneous infection.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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