U01.02.034 Infections in immunodeficiency

Understanding the relationship between immune deficiencies and susceptibility to specific pathogens is critical for USMLE Step 1 preparation. This guide provides a comprehensive overview of infections associated with T-cell, B-cell, granulocyte, and complement deficiencies.

Types of Pathogens and Immunodeficiencies

Bacteria

Deficiency	Pathogens
T Cells	Sepsis
B Cells	Encapsulated bacteria: SHINE my SKiS – Pseudomonas aeruginosa – Streptococcus pneumoniae – Haemophilus influenzae type b – Neisseria meningitidis – Escherichia coli – Salmonella – Klebsiella pneumoniae – Group B Streptococcus
Granulocytes	Specific bacteria: Some Bacteria Produce No Serious granules – Staphylococcus – Burkholderia cepacia – Pseudomonas aeruginosa – Nocardia – Serratia
Complement	– Encapsulated bacteria (early complement deficiencies) – Neisseria (late complement deficiencies, C5–C9)

Viruses

Deficiency	Pathogens
T Cells	– Cytomegalovirus (CMV) – Epstein-Barr virus (EBV) – JC virus – Varicella-zoster virus (VZV) – Chronic infections with respiratory/GI viruses
B Cells	– Enteroviral encephalitis – Poliovirus (avoid live vaccine)

Fungi and Parasites

Deficiency	Pathogens
T Cells	– Candida albicans (local infections) – Pneumocystis jirovecii (PCP) – Cryptococcus
B Cells	– Giardia lamblia (GI infections due to lack of IgA)
Granulocytes	– Candida albicans (systemic infections) – Aspergillus – Mucor

Points to Remember

T-cell Deficiencies
- Predispose to viral and fungal infections.
- Common pathogens: CMV, EBV, JC virus, and Candida (local).
B-cell Deficiencies
- Lead to recurrent bacterial infections, particularly with encapsulated organisms.
- Mnemonic: SHINE my SKiS for encapsulated bacteria.
Granulocyte Deficiencies
- Increase susceptibility to infections by catalase-positive organisms (e.g., Staphylococcus, Pseudomonas, Nocardia).
Complement Deficiencies
- Early complement deficiencies: Increased risk of encapsulated bacterial infections.
- Late complement deficiencies (C5–C9): Susceptibility to Neisseria.
Vaccination Caution
- Live vaccines (e.g., poliovirus) are contraindicated in patients with B-cell deficiencies due to the risk of severe infections.

Study Tips

Mnemonic Use: Learn and apply mnemonics like SHINE my SKiS and Some Bacteria Produce No Serious granules to recall bacterial pathogens.
Clinical Correlations: Familiarize yourself with clinical presentations of infections in immunocompromised patients (e.g., chronic diarrhea in IgA deficiency).
High-Yield Focus: Concentrate on distinguishing between infections in different immune deficiencies.

USMLE Step 1 Review Series

Curriculum