Nonleukopenic compromised hosts frequently have life-threatening infectious diseases that result in admission to the critical care unit (CCU). Nonleukopenic compromised hosts are those whose impaired host defenses are not related to a defect in the number of circulating lymphocytes. The commonest diseases associated with impaired host defenses not related to leukopenia are diabetes mellitus and systemic lupus erythematosus (SLE); the group also includes patients on corticosteroid therapy or those with absent or impaired splenic function. A wide variety of other disorders associated with immune defects, such as multiple myeloma, often are complicated by infection, but such infections are less likely to result in admission to the CCU than are infections in the aforementioned categories.

Infections in diabetes, lupus, or impaired splenic function often are severe and may be life-threatening. Intraabdominal infections, urinary tract infections (UTIs), and skin and soft tissue infections are the most common, resulting in severe infections in diabetics. Patients with lupus are subject to a wide variety of infections, usually involving the skin and soft tissues, central nervous system (CNS), urinary tract, or lungs. Long-term, high-dose steroid therapy primarily diminishes T-lymphocyte-dependent immunity, predisposing such patients to intracellular pathogens. Patients on chronic steroid therapy are predisposed to CNS infections, pulmonary infections, and disseminated infections due to intracellular bacteria, viruses, and systemic fungi.

The main diagnostic difficulty in the patient with SLE is to differentiate a lupus flare from infection. In patients with impaired or absent splenic function, overwhelming infection is the most dreaded complication, often having a fatal outcome. This article discusses the differential diagnostic approach of serious infections in these patients from the infectious disease perspective.