Microbiology · MU Sofia

112. Microbiological Aspects of Infections in Immunocompromised Patients

Covers the causes of immunosuppression, including HIV/AIDS, transplantation, chemotherapy, steroids and congenital defects, and the opportunistic bacterial, viral, fungal and protozoal pathogens linked to each. It then explains how neutropenia, T-cell, B-cell and barrier defects shape infection risk, lists key opportunistic infections by patient group, and outlines diagnostic tests, empirical treatment, prophylaxis and vaccination. Two summary tables group the causes and organisms.

Inside: 8 sections · 4 labelled pictures · 2 tables · 15 flashcards · 2 min

Topic 112 of 113 in the MU Sofia syllabus for Microbiology (Dental Medicine, Year 2). The free AceMed note covers it in 8 sections, about 214 words (2 min of reading), with 15 flashcards.

In this note

  1. Microbiological Aspects of Infections in Immunocompromised Patients
  2. I. Overview
  3. II. Common Causes of Immunosuppression
  4. III. Opportunistic Pathogens by System
  5. IV. Pathogenesis and Risk Factors
  6. V. Key Opportunistic Infections by Condition
  7. VI. Diagnosis
  8. VII. Treatment and Prevention

I. Overview

Immunocompromised patients have weakened or absent immune responses due to conditions like:

  • HIV/AIDS
  • Cancer chemotherapy
  • Organ or stem cell transplantation
  • Congenital immunodeficiencies
  • Use of corticosteroids or immunosuppressants

These patients are vulnerable to opportunistic infections (OIs) — caused by microbes that are usually harmless in healthy individuals.

IV. Pathogenesis and Risk Factors

  • Neutropenia → risk for bacterial and fungal infections (Pseudomonas, Candida, Aspergillus)
  • T-cell defects (e.g., AIDS, transplant) → viral and intracellular pathogens (CMV, Pneumocystis, Toxoplasma)
  • B-cell/IgG deficiency → recurrent encapsulated bacterial infections (S. pneumoniae, H. influenzae)
  • Disruption of barriers (mucosa, skin) → endogenous flora cause sepsis

V. Key Opportunistic Infections by Condition

  • AIDS (CD4 <200):
  • Pneumocystis jirovecii pneumonia
  • Cryptococcus meningitis
  • Toxoplasma brain abscess
  • CMV retinitis or colitis
  • Transplant patients:
  • CMV reactivation
  • Aspergillus, Nocardia, BK virus nephropathy
  • Neutropenic patients:
  • Candida, Aspergillus, Pseudomonas, Staph spp.

VI. Diagnosis

  • High suspicion is critical, even with subtle symptoms.
  • Methods include:
  • Blood cultures, CSF analysis, BAL (bronchoalveolar lavage)
  • PCR (e.g., for CMV, JC virus)
  • Galactomannan antigen, β-D-glucan (for fungal infections)
  • Imaging: chest CT for nodules (Aspergillus), MRI for toxoplasmosis

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