FUNGAL PNEUMONIA

Fungal pathogens are rare but important causes of pneumonia. They are important because they cause serious infections and can progress to death and because they are untreated by the broad-spectrum antibacterial antibiotics that are used empirically for community-acquired and hospital-acquired pneumonia. Yet they are rare, so initial high suspicion of fungal cause is not appropriate in an ordinary case of pneumonia. There are, however, certain specific details of the clinical illness in some cases of pneumonia that should raise suspicion that a fungal pathogen may be the causative agent. Each fungal pneumonia is discussed separately. Specific clinical clues to each illness are presented first, followed by current strategies for confirming the diagnosis and treating the infection. The separate diseases are organized into two main groups. First are diseases caused by T cell opportunists. Nonimmune phagocytes cannot kill the inhaled spores of these organisms.(25) Specific immunity must be engaged to control the infection. Macrophages must ingest the spores and present specific antigens to T cells. Specific immune T cells must replicate and ''arm'' other macrophages, which then slow fungal growth and wall off the invading fungi within granulomas. The implications of a requirement for specific immunity include (1) all nonimmune subjects can be infected if they inhale the spores; (2) symptoms are variable and depend somewhat on the number of spores inhaled and the magnitude of the immune response; (3) once specific immunity is engaged, the disease tends to be self-limited; and (4) subjects with impaired T cell function are at high risk for severe, rapidly progressive infections. Diseases caused by T cell oppor tunists include histoplasmosis, blastomycosis, coccidioidomycosis, paracoccidioidomycosis, and cryptococcosis. All have high potential for causing severe infections in human immunodeficiency virus (HIV)-infected persons and others with T cell defects, including organ transplant recipients and others treated with high doses of glucocorticoids and with other immunosuppressive therapy for a variety of malignant and nonmalignant disorders. Second are the diseases caused by the phagocyte opportunists. Nonimmune phagocytes, particularly neutrophils, can kill the inhaled spores of these agents.(25)