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INTRODUCTION

GUIDING QUESTIONS

  1. How should an immunocompromised host be classified, and why?

  2. Which pathogens most commonly infect neutropenic patients?

  3. Which pathogens are responsible for infection in patients with defects in cell-mediated immunity?

  4. How should bone marrow transplant patients be classified with regard to their host immune deficiencies?

  5. Do all immunocompromised hosts with fever require empiric antibiotics?

POTENTIAL SEVERITY

Rapid evaluation and empiric antibiotics are required in the febrile neutropenic patient. High-grade life-threatening bacteremia is common.

DEFINITION OF THE IMMUNOCOMPROMISED HOST

Medical advances in the management of malignancies and organ failure have given rise to a population of patients now commonly called immunocompromised hosts. An immunocompromised host is a patient with leukemia, lymphoma, or solid tumors who is receiving cytotoxic chemotherapy or other chemotherapy, or who has received a bone marrow transplant (including a stem cell transplant), or a solid organ transplant. Additionally, patients in whom immunosuppressive agents and immune modulators are being applied for inflammatory disorders are adding to this expanding population whose major host defense mechanisms are in some way not functioning optimally to combat environmental and endogenous organisms. Immune system failures result in infection not only by normally accepted human pathogens and human saprophytes but also by environmental organisms of low intrinsic virulence.

Another type of immunocompromised host that should be kept in mind is the patient with an immunodeficiency syndrome that has a genetic basis. Most of these patients become apparent in childhood, presenting with histories of recurrent sinopulmonary or skin infections, most often attributable to bacterial agents. The management of these patients is best handled in the pediatric literature.

Thus, in the truest sense, the population under discussion should be called the “medically or iatrogenically compromised host,” because the compromise results mainly from treatment of an underlying disease. Careful attention must also be paid to the splenectomized patient whose ability to clear encapsulated bacteria is compromised in the absence of opsonic antibody and who is susceptible to overwhelming sepsis caused mainly by pneumococcus and Haemophilus influenzae.

CLASSIFICATION OF THE IMMUNOCOMPROMISED HOST

Immunocompromised patients can be divided into three main groups (although overlaps in these populations exist, as will be discussed later in this chapter):

  1. Patients whose major defect is caused by cytotoxic therapy or irradiation, or both, with the major defect being neutropenia and mucosal barrier damage. This group can be further divided into low risk and high risk (see below).

  2. Patients whose major defect is suppression of cell-mediated immunity resulting from the administration of immunosuppressive agents to control organ rejection or inflammation and include biologics that inhibit TNF, interleukin 1 and 6 receptors, CD80/86 receptors on T cells and reduce B cells.

  3. Patients with both types of major defects.

These distinctions should be made at the initial patient encounter, because this assessment guides the clinician’s diagnostic approach, the decision to initiate ...

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