🛡️ Chapter 106: Infections in Immunocompromised Host

Primary & acquired immunodeficiencies · Neutropenia · Opportunistic infections · P. jirovecii · CMV · Aspergillus · Empirical therapy · HEPA filtration · Vaccination · Prophylaxis

🔍 Core Concepts: Infections in Immunocompromised Host

📌 Warning signs of PID
≥2 pneumonias/year, ≥4 ear infections, failure to thrive, recurrent abscesses, family history of PID, need for IV antibiotics.
🧬 Primary immunodeficiencies
Antibody (XLA, CVID), cellular (DiGeorge), combined (SCID), phagocyte (CGD), complement deficiencies.
🦠 Acquired immunodeficiencies
Chemotherapy, transplant, HIV, immunosuppressive drugs, malnutrition, diabetes, asplenia.
🫁 Pulmonary presentations
Rapid progression: PJP (P. jirovecii), CMV. Nodules/cavitation: Aspergillus, Nocardia. Slow: organizing pneumonia, drug toxicity.
🧪 Diagnostic approach
Blood cultures, BAL (PJP, CMV, fungi), serum galactomannan, beta-D-glucan, CMV PCR. Imaging (CT chest, head).
💊 Management principles
Empiric broad-spectrum antibiotics + antifungals. Early inotropes for septic shock. HEPA filtration for severe neutropenia. Treat underlying immunodeficiency (IVIG, G-CSF).
⚠️ Special considerations
Avoid live vaccines in severe PID. Prophylaxis: TMP-SMX (PJP), fluconazole (Candida), valganciclovir (CMV post-transplant).

🩺 Stepwise Management of Immunocompromised Host with Suspected Infection

1
Assess net state of immunosuppression
Neutropenia (ANC <500), cellular immunity (CD4 count), humoral (Ig levels), medications (steroids, chemotherapy), recent transplant, CMV/EBV status.
2
Early broad-spectrum empirical therapy
Febrile neutropenia: antipseudomonal beta-lactam (cefepime, meropenem) ± vancomycin (if line infection, MRSA risk). Add antifungal if prolonged neutropenia >7 days or clinical deterioration.
3
Aggressive diagnostic workup
Cultures (blood, urine, sputum/BAL), serum galactomannan, beta-D-glucan, CMV PCR, chest CT. Bronchoscopy with BAL for PJP, viruses, fungi. Consider CNS imaging if focal deficits.
4
Supportive care & isolation
HEPA filtration for neutropenia (<500). Contact + airborne precautions if respiratory virus suspected. Restrict visitors. Early vasopressors for septic shock (catecholamine-refractory common).
5
Targeted therapy and prophylaxis
Based on culture/PCR: TMP-SMX for PJP, ganciclovir for CMV, voriconazole for aspergillosis. Prophylaxis: TMP-SMX (PJP), fluconazole (Candida), valganciclovir (CMV high risk). Vaccinate pre-transplant.