Fungal susceptibility testing: where are we now?

Invasive fungal infections have been noted in increasing frequency in immunosuppressed patients and may be due to organisms that are less susceptible or frankly resistant to antifungal agents. Recently, standards have been established for testing both yeasts and moulds for susceptibility to antifungal agents. While these tests are increasingly available for clinical use, clinicians are faced with the challenge of whether these tests offer benefit in terms of management and when they should be obtained. In this review, the relevance of these tests is discussed, as are the clinical data, especially for yeasts, that support their use. In addition, the strategy of identifying yeasts to the species level as a means for predicting susceptibility is also discussed. While susceptibility testing of all fungal isolates is not necessary and not recommended, the judicious use of these tests and the role of the mycology laboratory in assisting in management of invasive fungal infection is also evaluated.