Chronic Granulomatous Disease (CGD) Infections

Chronic granulomatous disease (CGD) is a rare primary immunodeficiency disorder (incidence approximately 1 in 200,000-250,000 live births) caused by genetic defects in the phagocyte NADPH oxidase complex preventing the respiratory burst essential for intracellular killing of microorganisms by neutrophils, monocytes, macrophages, and eosinophils. Five genes encode NADPH oxidase components, defects in any of which cause CGD: CYBB (gp91-phox, X-linked, 65-70% of cases — most severe), CYBA (p22-phox, autosomal recessive, 5%), NCF1 (p47-phox, autosomal recessive, 20-25% — milder), NCF2 (p67-phox, autosomal recessive, 5%), NCF4 (p40-phox, autosomal recessive, very rare). Defective oxidative burst prevents conversion of molecular oxygen to superoxide and downstream reactive oxygen species (hydrogen peroxide, hypochlorous acid) that are bactericidal and fungicidal.

Pathophysiology: phagocytes can ingest microorganisms but cannot kill catalase-positive organisms (which destroy hydrogen peroxide produced by other mechanisms), explaining the characteristic spectrum of pathogens — Staphylococcus aureus (most common, 30-50%), Burkholderia cepacia complex (10-20%, often pneumonia/sepsis), Serratia marcescens (5-10%, osteomyelitis, lymphadenitis, abscess), Nocardia species (5%, pneumonia, brain abscess), Aspergillus species (15-30%, pneumonia, granulomas — major cause of mortality), Chromobacterium violaceum, Salmonella species, Granulibacter bethesdensis, Francisella philomiragia. Catalase-negative organisms (Streptococcus, Streptococcus pneumoniae) cause normal infections because phagocytes can use bacterial-produced hydrogen peroxide for killing. Granuloma formation results from impaired phagocyte function and persistent antigen exposure with chronic inflammatory response.

Clinical presentation typically begins in early childhood (median age 3 years) but later presentations occur (especially autosomal recessive forms), characterized by recurrent infections involving skin (abscesses, cellulitis, eczematous dermatitis), lymph nodes (suppurative lymphadenitis), lungs (recurrent pneumonia, lung abscess, fibrosis, Aspergillus infections), liver (hepatic abscesses with characteristic dense granulomas requiring surgical drainage), bone (osteomyelitis), gastrointestinal tract (granulomatous colitis resembling Crohn disease, perirectal abscess), genitourinary (urinary obstruction from bladder granulomas), brain (rare, brain abscess from Nocardia or Aspergillus). Inflammatory complications include lung fibrosis, hepatic granulomas, gastrointestinal strictures, autoimmune phenomena (lupus-like, IBD-like). Diagnosis: dihydrorhodamine (DHR) flow cytometry test (gold standard, demonstrates absent or reduced respiratory burst), nitroblue tetrazolium (NBT) test (older, less sensitive), genetic testing for CYBB and other genes (essential for carrier identification and prenatal diagnosis), neutrophil function studies. Treatment: lifelong antimicrobial prophylaxis with trimethoprim-sulfamethoxazole (reduces bacterial infections by 50-65%), antifungal prophylaxis with itraconazole (reduces fungal infections), interferon-gamma 1b (50 mcg/m2 three times weekly, reduces severe infections by 70%), aggressive treatment of acute infections with broad-spectrum antibiotics and antifungals, surgical drainage of abscesses, corticosteroids for inflammatory complications, hematopoietic stem cell transplantation (HSCT) is curative — increasingly recommended in young patients with HLA-matched donors before significant organ damage (overall survival 80-90% with reduced-intensity conditioning), gene therapy (autologous CD34+ cells transduced with functional CYBB) emerging therapy for X-linked CGD (clinical trials with promising results).