Infections in Transplant Recipients¶
Chapter 148 | Part 5: Infectious Diseases
KEY CLINICAL POINTS¶
- Transplant recipients (SOT, HCT, VCA) face heightened infection risks due to immunosuppression, with infections accounting for 15-40% of early mortality.
- Hematopoietic stem cell transplantation (HCT) involves conditioning regimens that eliminate immune systems, with autologous (auto-HCT) vs allogeneic (allo-HCT) differing in donor source and GVHD risk.
- Neutropenic fever is a critical early infection risk, requiring prompt broad-spectrum antibiotics and antifungal prophylaxis for fungal infections.
- CMV remains the most significant viral pathogen in SOT and HCT, with prophylaxis strategies including valganciclovir or letermovir.
- Fungal infections like Aspergillus and Candida are common, with posaconazole and echinocandins as key treatments, while antifungal prophylaxis is standard for SOT.
1. DEFINITION & OVERVIEW¶
Transplant recipients (solid organ transplant [SOT], vascular composite allograft [VCA], and hematopoietic stem cell transplantation [HCT]) face heightened infection risks due to immunosuppression. SOT and VCA require lifelong immunosuppression, while HCT involves temporary immunosuppression post-transplant. Infections are a leading cause of morbidity/mortality, with 15-40% of early deaths in HCT recipients.
Table 148-1: Common Sources of Infection After Hematopoietic Stem Cell Transplantation¶
| INFECTION SITE | VERY EARLY (<1 MONTH) | EARLY (BEFORE 100 DAYS) | LATE (>100 DAYS) |
|---|---|---|---|
| Disseminated | Aerobic bacteria (gram-negative, gram-positive), Candida, Aspergillus, CMV, EBV, Toxoplasma | Encapsulated bacteria (Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis) | |
| Skin and mucous membranes | HSV, Candida | HSV, VZV | |
| Lungs | Aerobic bacteria (gram-negative, gram-positive), Aspergillus, other molds | CMV, community-acquired respiratory viruses, Pneumocystis, Toxoplasma, Nocardia, S. pneumoniae, H. influenzae | Community-acquired respiratory viruses, Pneumocystis, NTM (cGVHD) |
| Gastrointestinal tract | CMV, adenovirus, norovirus | EBV, CMV, norovirus | |
| Genitourinary tract | BK virus | BK virus, adenovirus |
| INFECTION SITE | VERY EARLY (<1 MONTH) | EARLY (BEFORE 100 DAYS) | LATE (>100 DAYS) |
|---|---|---|---|
| Brain | HHV-6, Toxoplasma | Toxoplasma, JC virus (rare) | |
| Bone marrow | CMV, Toxoplasma | CMV |
1.1 Hematopoietic Stem Cell Transplantation (HCT)¶
HCT involves conditioning regimens that eliminate immune systems, followed by stem cell infusion. Auto-HCT uses the recipient's own cells, while allo-HCT uses donor cells. Allo-HCT carries risks of graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effects.
1.2 Solid Organ Transplantation (SOT)¶
SOT requires lifelong immunosuppression to prevent rejection. Common infections include CMV, PJP, and fungal infections. Prophylaxis strategies vary by organ type and immunosuppressive regimen.
1.3 Vascular Composite Allografts (VCA)¶
VCAs involve complex surgical procedures with high infection risks due to anatomical complexity. Bacterial infections are common, with prophylaxis strategies similar to SOT.
2. EPIDEMIOLOGY¶
Infections are a major cause of morbidity/mortality in transplant recipients. Incidence varies by transplant type: 15-25% of deaths in auto-HCT within 100 days, 20-40% in allo-HCT. Risk factors include preexisting conditions, conditioning regimens, immunosuppression, and donor/recipient factors.
2.1 Incidence and Prevalence¶
Infections account for 15-40% of early mortality in HCT recipients. SOT recipients face higher risks of fungal infections (e.g., Aspergillus, Candida) and viral reactivations (CMV, EBV).
2.2 Risk Factors¶
Preexisting immunodeficiencies, conditioning regimens (myeloablative vs. nonmyeloablative), immunosuppressive drugs (cyclosporine, tacrolimus), and donor/recipient serostatus (e.g., D+/R– for CMV) increase infection risks.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Immunosuppression disrupts immune defenses, allowing opportunistic pathogens to thrive. Key mechanisms include neutropenia, mucosal barrier damage, and immunosuppressive drug interactions. Viral reactivation (CMV, EBV), fungal infections (Aspergillus, Candida), and bacterial infections (Pseudomonas, Staphylococcus) are common.
3.1 Immunosuppression and Opportunistic Infections¶
Immunosuppressive drugs (e.g., corticosteroids, calcineurin inhibitors) increase susceptibility to opportunistic pathogens. Neutropenia and mucosal damage from conditioning regimens further predispose to infections.
3.2 Viral Reactivation¶
CMV, EBV, HHV-6, and HSV reactivation are common due to immunosuppression. CMV is the most significant viral pathogen in SOT and HCT.
4. CLINICAL FEATURES¶
Infections present with varied symptoms depending on the pathogen and transplant type. Neutropenic fever, fungal infections (e.g., Aspergillus), and viral reactivations (CMV, EBV) are critical to recognize early.
4.1 Neutropenic Fever¶
Fever during neutropenia is common in HCT recipients. It is considered infectious in origin, requiring prompt broad-spectrum antibiotics (e.g., piperacillin-tazobactam) and antifungal prophylaxis.
4.2 Fungal Infections¶
Invasive fungal infections (e.g., Aspergillus, Candida) are common in SOT and HCT recipients. Symptoms include fever, cough, and respiratory distress.
5. DIFFERENTIAL DIAGNOSIS¶
Infections in transplant recipients must be differentiated from other conditions like GVHD, rejection, and drug toxicity. Key differentials include viral reactivations, bacterial infections, and fungal infections.
5.1 Viral Reactivations¶
CMV, EBV, HSV, and VZV reactivations must be distinguished from bacterial infections and fungal infections. PCR testing and serology are critical for diagnosis.
5.2 Bacterial vs. Fungal Infections¶
Bacterial infections often present with localized symptoms (e.g., urinary tract infections), while fungal infections (e.g., Aspergillus) may present with systemic symptoms like fever and respiratory distress.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic workup includes clinical evaluation, imaging, and laboratory tests. Molecular diagnostics (PCR) and serology are essential for identifying pathogens like CMV, EBV, and fungal antigens.
6.1 Laboratory Tests¶
Blood cultures, PCR for viral DNA, and antigen detection (e.g., galactomannan for Aspergillus) are critical. Serologic testing for EBV, CMV, and Toxoplasma is also important.
6.2 Imaging¶
Chest X-rays, CT scans, and MRI are used to assess lung, brain, and abdominal infections. Ultrasound may be used for urinary tract infections.
7. MANAGEMENT & TREATMENT¶
Management includes antimicrobial prophylaxis, antifungal therapy, and antiviral treatment. Supportive care, immunosuppression adjustment, and source control are critical.
Table 148-3: Prophylactic Regimens for Transplant Recipients¶
| RISK FACTOR | ORGANISM | PROPHYLACTIC DRUG | EXAMINATION(S) |
|---|---|---|---|
| Neutropenia, mucositis | Candida | Fluconazole | Candida is part of the normal GI flora; everyone with disruption of the mucosal integrity is at risk |
| Prolonged neutropenia, high-dose corticosteroids | Aspergillus and other molds | Posaconazole | Blood tests (GMN, b-d-glucan) are less sensitive if triazoles are being administered |
| Travel to endemic fungal infection areas | Histoplasma, Blastomyces, Coccidioides | Triazoles | Chest imaging, antigen testing, serology |
| Chronic hepatitis B | HBV | Entecavir | HBV serology, HBV DNA |
| Latent herpesviruses | HSV, VZV, CMV, EBV | Acyclovir or valacyclovir | Serologic tests for HSV, VZV, CMV, HHV-6, EBV, KSHV (HHV-8); PCR |
| Exposure to Pneumocystis | Pneumocystis jirovecii | Trimethoprim-sulfamethox azole (TMP-SMX) | Second line: dapsone, pentamidine, atovaquone |
| Toxoplasma gondii | Toxoplasma gondii | TMP-SMX or atovaquone | |
| Strongyloides stercoralis | Strongyloides stercoralis | Ivermectin | |
| LTBI | Mycobacterium tuberculosis | Isoniazid or rifampin | TST and/or IGRA; if indeterminate, clinical assessment of exposure and risk |
7.1 Antimicrobial Prophylaxis¶
Prophylaxis for PJP (TMP-SMX), CMV (valganciclovir/lemtermovir), and fungal infections (posaconazole) is standard. Prophylaxis for BK virus and candidiasis is also used.
7.2 Antifungal Therapy¶
Echinocandins (e.g., caspofungin) are first-line for invasive candidiasis. Posaconazole is used for Aspergillus and other molds. Antifungal prophylaxis is routine for SOT recipients.
8. PROGNOSIS & COMPLICATIONS¶
Infections in transplant recipients can lead to severe complications, including graft loss, organ failure, and mortality. Prognosis depends on infection type, timing, and response to treatment.
8.1 Complications¶
Infections may lead to graft loss, sepsis, and multiorgan failure. Chronic GVHD and immunosuppression increase the risk of opportunistic infections.
8.2 Mortality¶
Infections account for 15-40% of early mortality in HCT recipients. Fungal infections (e.g., Aspergillus) and CMV disease are associated with high mortality.
9. SPECIAL CONSIDERATIONS¶
Special populations (pregnancy, pediatrics, elderly) require tailored approaches. Pregnancy in SOT recipients requires careful management of immunosuppression and antiviral prophylaxis.
9.1 Pregnancy¶
Immunosuppressive drugs (e.g., tacrolimus) require dose adjustments. CMV prophylaxis is critical to prevent congenital transmission.
9.2 Pediatrics¶
Pediatric HCT recipients face higher risks of viral reactivation and fungal infections. Prophylaxis strategies must account for growth and development.
10. KEY POINTS & CLINICAL PEARLS¶
- Neutropenic fever requires prompt broad-spectrum antibiotics and antifungal prophylaxis.
- CMV is the most significant viral pathogen in SOT and HCT, with prophylaxis strategies including valganciclovir or letermovir.
- Fungal infections like Aspergillus and Candida are common, with posaconazole and echinocandins as key treatments.
- Prophylaxis for PJP, BK virus, and fungal infections is standard in transplant recipients.
- Early diagnosis and treatment of infections are critical to prevent graft loss and mortality.