Pathology of common pulmonary fungal infections

The incidence of fungal pneumonias has increased dramatically since the 1960s, particularly in immunocompromised patients. Fungal infections may be divided into endemic and opportunistic varieties. In general, the truly pathogenic (endemic) fungi infect healthy individuals, and opportunistic fungi usually infect only immunocompromised hosts. Almost all common fungal infections are acquired by inhalation of contaminated soil, resulting in pulmonary infections. Once in the lungs, the fungi elicit tissue responses ranging from acute exudative reactions to granulomatous reactions. The pulmonary lesions may resolve, progress to a prolonged chronic course, or disseminate to other organs, resulting in systemic infections. The diagnosis of fungal infection depends on the demonstration of the organisms by culture or histology; serologic tests may confirm the diagnosis. Fungi in tissues can be identified by hematoxylin and eosin stains, but special stains such as Gomori's methenamine silver and periodic acid-Schiff reagent are often required for diagnosis.