Immunocompromised Host and Transplant Infectious Diseases
Core concepts
Know the timeline of post-transplant infections: early (first month-surgical, nosocomial, Candida), intermediate (1-6 months-opportunistic: CMV, PJP, Aspergillus, Listeria), and late (>6 months-community-acquired, late CMV). In neutropenic fever, start empiric anti-pseudomonal beta-lactam (cefepime, piperacillin-tazobactam, or meropenem).
Must-know syndromes
PJP (TMP-SMX; steroids if hypoxic), CMV (valganciclovir), Aspergillus (voriconazole), Cryptococcus (amphotericin + flucytosine), and post-transplant lymphoproliferative disorder (EBV). In HIV, CD4 thresholds guide prophylaxis: PJP <200, Toxoplasma <100, MAC <50.
Traps
Don't miss atypical infections in asplenic patients (encapsulated organisms-vaccinate and give prophylaxis). Graft-versus-host disease increases infection risk. Post-transplant patients may not mount fever-low threshold for imaging and cultures. Drug interactions between immunosuppressants (tacrolimus) and azoles (CYP3A4) are common.
Worked rule of thumb
For a neutropenic patient with fever, obtain cultures and start empiric anti-pseudomonal beta-lactam within 1 hour. Do not wait for culture results. Add vancomycin only for suspected line infection, MRSA, or hemodynamic instability.