Utilizing Rapid Diagnostics for Detection of Candida Species

Abstract

Rapid diagnostic tests are now available to aid in the detection of invasive candidiasis (IC) and promise significant advantages to conventional detection and identification methods. The most progress has been made on rapid species identification when blood culture bottles turn positive and/or when isolated pure colonies are available, while the diagnosis of IC directly from a clinical specimen (e.g., the patient’s blood) remains problematic. For the latter, nucleic acid-based tests (PCR, PCR/electrospray ionization-mass spectrometry (PCR/ESI-MS), and T2 magnetic resonance) and immunologic tests [1,3-β-D-glucan (BG) and Candida antigen and antibody tests] are promising but each contains certain limitations which have restricted their impact on clinical practice. In-house PCR assays are not standardized, and commercially available PCR tests are limited by minimal clinical data and a long turnaround time. The PCR/ESI-MS and T2 magnetic resonance platforms both require substantial up-front resources, and further clinical experience is required to understand their role in the clinical laboratory. Also, the BG and Candida antigen and antibody tests may be useful in certain scenarios (e.g., a negative BG may help rule out IC) but require significant clinical correlation and interpretation of results. On the other hand, PNA FISH and FilmArray Blood Culture ID Panel can substantially reduce the time-to-identification from a positive blood culture, impact clinical practice, and are quite reasonable to implement in the clinical laboratory. While the clear advantages for MALDI-TOF MS are speed, versatility, and excellent accuracy for identification of organisms from culture plates (which is its primary use in the clinical laboratory), further optimization is required before it can reliably be used for organism identification directly from blood culture bottles and its cost is currently prohibitively expensive for a small clinical laboratory. MALDI-TOF MS is very appealing, however, for rapid identification of organisms in a large clinical laboratory. All of these rapid diagnostic methods complement but do not replace the culture, however, as having the organism itself is still critical for susceptibility testing and strain typing