Laboratory detection of fungemia

Patients who are immunosuppressed, receiving broad-spectrum antibiotics, or with intravascular catheters in place are at risk for invasive fungal infections. In a significant number nosocomial fungal infections develop. The diagnosis of invasive fungal disease often relies on the detection of the etiologic agent using blood cultures. Great progress has been made in fungal blood culturing over the past 20 years with the development of biphasic media, automated radiometric and nonradiometric systems, and LCS used with selective culture media. The biphasic BHI and Septi-Chek systems provide recovery of the majority of fungal isolates, yet there frequently is an undesirable delay in detection. Lysis of blood cells, aeration by venting, and agitated incubation improve detection with these systems. Automated systems often require a significant initial financial investment but have been shown to be durable and effective in most aspects of blood culturing. They have a limited daily hands on requirement. The newer nonradiometric systems appear to be better than the older systems, especially in time to detection and in the reduction of false-positive signals. The most significant factors, however, may be the volume of blood used in these systems and the resins incorporated in the media to eliminate inhibitors of fungal growth. A significant disadvantage of the automated systems has been their failure to detect certain organisms (C. neoformans and dimorphic fungi); however, the use of newer culture media as well as blind subculturing may partially alleviate this problem. Lysis-centrifugation blood culturing has performed well, is highly sensitive, and permits recovery of both fungi and aerobic bacteria. Because it is flexible, the media selection can be altered to suit any specific growth requirement. It is rapid and permits the identification of most yeast and yeastlike microorganisms within 4 days and of H. capsulatum within 3 weeks. Because this system utilizes solid media, blind subculturing is unnecessary. Quantitation of fungemia is possible and may permit determination of the clinical importance of the microorganism and assessment of the patient's response to treatment. The disadvantages of this system are that it requires a significant amount of the technologist's time to process the specimen, inoculate the various media, and visually examine the culture media throughout the incubation period. A significant contamination rate still exists despite working within a laminar flow biosafety cabinet; this also increases time requirements. The detection of fungemia has markedly improved; the times to detection have decreased to the point of being clinically useful, and several systems are available to accommodate individual laboratory needs.(ABSTRACT TRUNCATED AT 400 WORDS)