ABSTRACT
Identified in 1909, an organism of the Pneumocystis genus, namely Pneumocystis jirovecii, remains today an important pathogen of immunocompromised human hosts. To distinguish the species of Pneumocystis that infects humans from the species that infects rats, the nomenclature of the former was changed from P. carinii to P. jirovecii. P. jirovecii causes Pneumocystis pneumonia, particularly in patients with compromised immune systems due to malignancy, human immunodeficiency virus (HIV) infection with CD4+ lymphocyte counts <200 cells/μL, or as the result of hematopoietic or solid organ transplantation. Pneumocystis pneumonia typically presents clinically with fulminant respiratory failure, fever, cough, and hypoxemia, and radiographically with diffuse interstitial infiltrates. Definitive diagnosis of Pneumocystis pneumonia requires identification of the organism with dye-based or antibody staining, or by the use of polymerase chain reaction. Definitive diagnosis of Pneumocystis pneumonia requires identification of the organism either by dye-based or fluorescent antibody staining, or by polymerase chain reaction assays of respiratory specimens. Trimethoprim-sulfamethoxazole is a first-line therapy both for treatment and prevention of the disease.
