Infection in the Immunocompromised Patient

KEY FEATURES

Essentials of Diagnosis

• Fever and other symptoms may be blunted because of immunosuppression

• A contaminating organism in an immunocompetent individual may be a pathogen in an immunocompromised one

• The interval since transplantation and the degree of immunosuppression can narrow the differential diagnosis

• Empiric broad-spectrum antibiotics may be appropriate in high-risk patients whether or not symptoms are localized

General Considerations

Impaired Humoral Immunity

• Risk factors

  • Plasma cell myeloma

  • Chronic lymphocytic leukemia (and small lymphocyte lymphoma)

  • Acquired and congenital hypogammaglobulinemia

  • Asplenia

• Increased infections with encapsulated organisms such as Haemophilus influenzae and Streptococcus pneumoniae

• Although normally thought of as being linked to impaired cellular immunity, there is an association between rituximab (anti-B cell monoclonal antibody) therapy and development of

  • Pneumocystis jirovecii infection

  • Progressive multifocal leukoencephalopathy (PML)

  • Hepatitis B (HBV) reactivation

Granulocytopenia (Neutropenia)

• Risk factor is absolute granulocyte count below 1000/mcL (1.0 × 10⁹/L), and especially below 100/mcL (0.1 × 10⁹/L)

• Increased infections with:

  • Gram-negative enteric organisms (particularly Pseudomonas)

  • Gram-positive cocci (particularly Staphylococcus aureus, Staphylococcus epidermidis, and viridans streptococci)

  • Candida

  • Aspergillus

  • Other fungi such as Trichosporon, Scedosporium, Fusarium, and the mucormycoses

Impaired Cellular Immunity

• HIV infection, lymphoreticular malignancies such as Hodgkin disease, immunosuppressive medications

• Increased infections by a large number of

  • Bacteria, such as Listeria, Legionella, Salmonella, and Mycobacteria

  • Viruses, such as herpes simplex, varicella, and cytomegalovirus (CMV)

  • Fungi, such as Cryptococcus, Coccidioides, Histoplasma, and Pneumocystis

  • Protozoa, such as Toxoplasma

Hematopoietic Cell Transplant Recipients

• In the early (preengraftment) posttransplant period (days 1–21), patients become severely neutropenic and are at risk for gram-positive and gram-negative bacterial infections, herpes simplex virus, respiratory syncytial virus, and fungal infections

• Source of fever is unknown in 60–70% of hematopoietic cell transplant patients during this period

• Between 3 weeks and 3 months posttransplant, common infections include CMV, adenovirus, Aspergillus, Candida, and the possibility of Pneumocystis jirovecii pneumonia

• Risk of infectious complications continues beyond 3 months, particularly in allogeneic transplant recipients and those on immunosuppressive therapy for chronic graft-versus-host disease; varicella-zoster, Aspergillus, and CMV are increasingly seen in this period

Solid Organ Transplant Recipients

• Immediate postoperative infections often involve the transplanted organ, with lung transplantation associated with pneumonia and mediastinitis, liver transplantation with intra-abdominal abscess, cholangitis, and peritonitis, and kidney transplantation with urinary tract infections, perinephric abscesses, and infected lymphoceles

• Infections within the first 2–4 weeks posttransplant are typically related to the operative procedure, hospitalization, or the transplanted organ itself

• Donor-derived infections rarely occur during this period

• Infections between the first and sixth months posttransplant are often related ...