The evolving role of antifungal susceptibility testing

Although increasing numbers of hospital microbiology laboratories are performing antifungal susceptibility testing (AST), its routine use is uncommon. The utility of AST is founded on the belief that susceptibility (or resistance) of an agent allows some prediction of clinical outcome. This review provides an overview of the development of antifungal susceptibility testing methodology, including wild-type minimum inhibitory concentration (MIC) distributions, epidemiologic breakpoints, and Interpretive Clinical Breakpoints for antifungal agents. In addition, we examine the current clinical utility of AST and the clinical data support utilized in the development of clinical breakpoints (CBP) for common pathogens causing invasive fungal infections. In the treatment of fungal infections, identifying consistent correlations between MICs - or susceptibility category - and clinical outcomes is an ongoing challenge, and current data sets are insufficient for many drugs and pathogens to enable the development, revision, or confirmation of CBPs. Antifungal susceptibility testing is of current value, but further research in many areas is needed before MICs are independently used to guide treatment decisions.