The yeast Candida and mold Aspergillus represent two of the most important classes of fungi in clinical medicine. They live in virtually every environment, and hospitals are no exception. Perhaps they are best known as causes of vaginitis (Candida) and pulmonary hypersensitivity (Aspergillus). Healthy hosts suffer from these localized conditions, but by virtue of intact physical barriers and active immune surveillance, do not develop disseminated infections. For susceptible patients, however, disseminated Candida and Aspergillus are common concerns. These multi-system infections remain difficult to diagnose and frequently end in death, with mortality rates such as 50% for disseminated candidiasis. As opportunistic infections, these fungi show an affinity for the critically ill, for example in the setting of immunosuppression, chemotherapy, transplantation, hyperalimentation, burns, and ulcers. With advances in critical care, oncology, and transplant medicine, more and more patients enter the ranks of those susceptible to disseminated disease.
With the advent of medications such as voriconazole, liposomal amphotericin, intravenous itraconazole, and caspofungin, treatment can be effective if instituted early. This has placed renewed emphasis on the need for early diagnosis of disseminated Candida and Aspergillus. Unless a specific nidus of infection is suspected (for example, a pulmonary Aspergillus lesion), a mainstay of diagnosis is blood cultures, which have suboptimal speed and sensitivity (estimated at 50% in some series). Aspergillus, which is usually acquired by the airborne route, can be identified microscopically from bronchoscopy samples, but sensitivity is still only 50%. Traditionally, clinicians have been forced to start empiric antifungal therapy in response to any unexpla