Current epidemiology and implication for microbiological diagnosis of cryptococcal infections in Korea

Cryptococcosis is a major invasive fungal infection affecting both immunocompromised and immunocompetent hosts worldwide and is mainly caused by Cryptococcus neoformans and Cryptococcus gattii. C. neoformans accounts for 90% of all infections and primarily causes central nervous system infections. Although C. gattii is primarily found in tropical and subtropical regions, infections have recently been reported in temperate areas such as Korea. Genetic studies in Korea indicated that most C. neoformans strains are of the VNIST5 type and show genetic homogeneity. In contrast, genetic studies on C. gattii are limited. Cryptococcosis is diagnosed using microscopy, serological tests, culture, and molecular tests. Although it can be detected in the cerebrospinal fluid or body fluids using the India ink method, confirmation through culture is essential for a definitive diagnosis. Cryptococcal antigen testing is economical, highly sensitive, and specific; therefore, it is widely used for the diagnosis of cryptococcosis. Molecular methods have recently been introduced; however, their applications remain limited. The recommended treatment for cryptococcal infections includes amphotericin B alone or in combination with flucytosine or fluconazole. Secondary resistance to flucytosine and fluconazole is common. The Clinical and Laboratory Standards Institute and European Committee on Antimicrobial Susceptibility Testing recommend the broth microdilution method. Several commercial methods for antifungal susceptibility testing have been developed and are currently in use; however, more data are required to establish breakpoints.