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Chronic Granulomatous Disease — SCE Infectious Diseases MCQ

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ModerateImmunocompromised HostChronic Granulomatous DiseaseSCE Infectious Diseases

A 45-year-old man with chronic granulomatous disease (CGD) presents with a liver abscess. CT-guided aspiration yields thick yellow pus. Gram stain shows Gram-positive cocci in clusters. Culture grows Staphylococcus aureus. What feature of CGD predisposes to S. aureus infections?

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Correct answer: E — Defective neutrophil oxidative burst (NADPH oxidase deficiency) — neutrophils cannot produce superoxide to kill catalase-positive organisms

CGD is caused by mutations in the NADPH oxidase complex (most commonly X-linked gp91phox deficiency), resulting in defective neutrophil (and macrophage) oxidative burst. Phagocytes can ingest bacteria but cannot generate the reactive oxygen species needed to kill them. Catalase-positive organisms (S. aureus, Burkholderia cepacia, Serratia marcescens, Nocardia, Aspergillus) are particularly problematic because they neutralise the small amount of hydrogen peroxide generated by the bacteria themselves. Catalase-negative organisms (Streptococci) generate enough H2O2 to partially compensate.

Reference: UK PID guidelines 2023 – CGD; NICE 2024 – Primary immunodeficiency