[Defects in the host defense system predisposing the patient to infection].

The normal host defense mechanisms against infection include (1) normal skin and mucous membranes, (2) phagocytic system, (3) humoral immunity, and (4) cellular immunity. The compromised host is an individual who has one or more defects in these defense mechanisms. Defects in each aspect of host defense increase the risk of infection caused by specific groups of microorganisms. Knowledge of these defects and potential infections in the compromised host will guide the initial (empiric) selection of antibiotics, the dosage and duration of antibiotic therapy, and decisions regarding antibiotic prophylaxis and the use of immunomodulators that are likely to augment host defenses.