Background

Cryptococcus neoformans is an encapsulated yeast. In 1984, a pathologist named Busse first described the yeast in a paper he presented to the Greifswald Medical Society. Busse isolated the yeast from the tibia of a 31-year-old woman, noted its resistance to sodium hydroxide, and published the case report that same year. The following year, a surgeon named Buschke reported the same isolate from the same patient, thus establishing the early eponym of Busse-Buschke disease. This single case served to identify a new yeast and to prove its pathogenic potential.

Since the initial reports, researchers have identified the diverse spectrum of host responses to cryptococcal infection. The responses range from a harmless colonization of the airways and asymptomatic infection in laboratory workers (resulting in a positive skin test result) to meningitis or disseminated disease. Although virulence in animals and, possibly, humans varies among strains of cryptococci, virulence probably plays a relatively small role in the outcome of an infection. The crucial factor is the immune status of the host. The most serious infections usually develop in patients with defective cell-mediated immunity. For example, patients with AIDS, patients undergoing organ transplantation, patients with reticuloendothelial malignancy, patients undergoing corticosteroid treatment (but not those with neutropenia or immunoglobulin deficiency), and patients with sarcoidosis develop the most serious infections.

With the global emergence of AIDS, the incidence of cryptococcosis is increasing and now represents a major life-threatening fungal infection in these patients.