Research Highlights

Abstract

Treating and diagnosing opportunistic infections in immunosuppressed patients remains a very important aspect for all clinicians working in the field of transplantation. Candidiasis is the most common fungal infection in hospitalized patients, and for this reason, the correct diagnosis of some of the important Candida albicans or non-albicans Candida species is essential, as invasive candidiasis caused by non-albicans is associated with higher resistance rates.1,2 Mylonakis and coworkers estimated mortality rates in patients who received antifungal therapy immediately after blood cultures to be 24% while a delayed treatment starting on days 2 and 3 increased mortality rates to 37% and 41%, respectively. Candida species are traditionally diagnosed by using microscopy, histopathology, culture, plating samples on chromogenic culture media as well as identifying enzyme, metabolite, structural components of the cell wall (1,3-β-D-glucan), antibody (antimannan) or antigen (mannan). PCR testing comes with shortcomings as well and has not yet been accepted as standard of care. Blood cultures and 1,3-β-D-glucan assays have not been specific for Candida leading to potential false-positive results. Rapid Identification of Medically Important Candida Isolates Using High Resolution Melting Analysis Nemcova E, Cernochova M, Ruzicka F, Malisova B, Freiberger T, Nemec P. PloS ONE. 2015;10(2):e0116940 In this report, the authors describe a combination of real-time polymerase chain reaction (PCR) and high-resolution melting analysis (HRMA) for the rapid detection of 25 medically important Candida species. Real-time PCR followed by HRMA showed reproducible melting peaks for 21 of 25 Candida species. Misidentification occurred with C. orthopsilosis, C. metapsilosis, and C. fabianii. Clinically, the correct diagnosis of C. parapsilosis is significant as this strain is less susceptible to antifungals. Notably all C. parapsilosis were clearly distinguishable from other strains using this method. This is the widest range of Candida species ever tested and identified using the HRMA method including a large number of 143 clinical isolates covering 23 species for validation. Real-time PCR followed by HRMA appears as an efficient and simple method diagnosing most candida species. Of note, the diagnosis can be made within 6 hours based on HRMA compared to 24 to 48 hours with the biochemical methods. T2 magnetic resonance assay for the rapid diagnosis of candidemia in whole blood: a clinical trial. Mylonakis E, Clancy CJ, Ostrosky-Zeichner L, et al. Clin Infect Dis. 2015;60(6):892–899 A nanodiagnostic method using a manual application of T2 magnetic resonance (T2MR) was used in this study to diagnose 5 Candida species: C. albicans, C. tropicalis, C. Krusei, C. glabrata and C. parapsilosis. A total of 250 blood culture samples were manually supplemented with clinically relevant titres of the above Candida species and 50 samples were used as negative controls. These samples formed the contrived or control arm of the study, and they were randomly inserted into the 2264 clinical specimens to check how different titres of Candida would react to the methodology. A total of 463 samples were excluded for technical errors or invalid results. The results of the primary analysis showed an overall specificity of 99.4% per assay and 98.1% per patient. Importantly, the mean time to obtain a negative result was only 4.2 hours compared to longer than 120 hours for a blood culture (BCT). There were 31 discordant cases between T2MR and blood culture: 2 had positive BCT and negative T2MR and 29 negative BCT but positive T2MR. This can be related to either false-positive T2MR or false negative BCT. The BCT methods are known to have poor sensitivity, and clinical samples are shown to be positive in only 38% of proven invasive candidiasis.3 Therefore, it is very likely that these cases represent Candida species infections that were missed by BCT. Importantly, this new technology has a high sensitivity in identifying non-albicans Candida like C. glabrata for which this test has an overall sensitivity of 84%. This study represents the first extensive clinical trial using T2MR technology. REFERENCES Wisplinghoff H, Bischoff T, Tallent SM, et al. Nosocomial bloodstream infections in US hospitals: analysis of 24,179 cases from a prospective nationwide surveillance study. Clin Infect Dis. 2004;39(3):309–317. Chi HW, Yang YS, Shang ST, et al. Candida albicans versus non-albicans bloodstream infections: the comparison of risk factors and outcome. J Microbiol Immunol Infect. 2011;44(5):369–375. Avni T, Leibovici L, Paul M. PCR diagnosis of invasive candidiasis: systematic review and meta-analysis. J ClinMicrobiol. 2011;49(2):665–670.