Bacterial infections in the compromised host.

Patients with defects in host defence mechanisms represent an important and increasing problem in medicine. While severe, primary immunodeficiency diseases are rare, patients with secondary or acquired immunodeficiency disorders are commonly encountered, particularly in hospital medicine. The cause of these secondary immunodeficiency states is either the underlying disease or iatrogenic factors associated with therapeutic regimens, often a combination. A particular pattern of infections and pathogens may to some extent be characteristical of the type of immunodeficiency present and may therefore be commonly associated with certain diseases and clinical conditions. With the important reservation that a considerable overlap frequently occurs between patterns of defects and infections in different disorders, it is convenient to classify immunocompromised patients in three broad groups according to their predominant defect: 1) neutropenia, 2) deficient cell-mediated (T-cell-mediated) immunity, and 3) deficient humoral (B-cell-mediated) immunity. A survey is given of some important bacterial infections in patients with these three types of immunodeficiency with particular emphasis on the neutropenic patient. It is emphasized that an aggressive approach to diagnosis and treatment of infections in immunocompromised patients is justified since antibiotic treatment differs considerably according to bacterial etiology, and chemotherapy is also available for a number of infections with fungi, protozoa and viruses.