Pneumocytis jiroveci is an opportunistic fungal pathogen that has gained particular prominence since the onset of the AIDS epidemic. Because of the relatively high incidence of pneumocystis pneumonia complicating HIV infection, it is often termed the AIDS-defining illness.
However, despite this many questions about its epidemiology and transmission remain unanswered. Whereas traditional theory postulates that the disease results from reactivation of latent infection, recent data suggest that active acquisition of infection, either through environmental exposure or through person-to-person transmission, may occur.
This article summarizes current knowledge on biology, pathophysiology and epidemiology of pulmonary P. jiroveci infection.