Theel, Elitza S.

ABSTRACT Histoplasma urine antigen (UAg) detection is an important biomarker for histoplasmosis. The clinical significance of low-positive (<0.6 ng/ml) UAg results was evaluated in 25 patients without evidence of prior Histoplasma infection. UAg results from 12/25 (48%) patients were considered falsely positive, suggesting that low-positive UAg values should be interpreted cautiously.

ABSTRACT Detection of Histoplasma capsulatum urinary antigen (UAg) is important for the initial diagnosis of infection and for monitoring of patient responses to antifungal therapy. This study evaluated an analyte-specific reagent (ASR) enzyme immunoassay (EIA) for the detection of H. capsulatum UAg from Immuno Mycologics, Inc. (IMMY) (Norman, OK) in comparison with routine testing with the MiraVista (MVista) H. capsulatum quantitative EIA (MiraVista Diagnostics, Indianapolis, IN). Using prospectively collected urine specimens ( n = 1,003), we observed an overall percent agreement between the two assays of 97.6% (979/1,003 samples). Compared with the MVista EIA, the sensitivity and specificity of the IMMY ASR EIA were 64.5% (40/62 samples) and 99.8% (939/941 samples), respectively, using a cutoff value of 0.5 ng/ml. Based on available clinical histories for 23/24 discordant samples, 5 IMMY assay-negative/MVista assay-positive samples were considered falsely positive. Furthermore, 10/23 discordant samples were positive by the MVista EIA but were below the limit of quantitation (<0.4 ng/ml). The clinical significance of these low positive results in the MVista EIA is unclear. In addition to the prospective study, we tested 11 urine specimens collected from patients with culture-confirmed Histoplasma infections, and 100% (11/11 samples) were positive by the IMMY ASR EIA. In conclusion, the IMMY ASR EIA may offer an alternative approach for the detection of Histoplasma UAg. Additional prospective studies are needed to better characterize the performance of the IMMY ASR EIA in conjunction with clinical and laboratory findings.

ABSTRACT Invasive fungal infections are a significant cause of morbidity and mortality in patients who receive immunosuppressive therapy, such as solid organ and hematopoietic stem cell transplant (HSCT) recipients. Many of the fungi associated with these infections are angioinvasive and are best diagnosed by visualizing the organism in or culturing the organism from deep tissue. However, obtaining such tissue often requires an invasive procedure. Many HSCT recipients are thrombocytopenic, making such procedure too risky because of potential bleeding complications. Additionally, positive blood cultures are rare for patients with angioinvasive fungal infections, making this diagnostic strategy of little value. Undiagnosed fungal infections in these patient populations are a significant cause of mortality. Prophylactic use of antifungal agents, such as the echinocandins, during periods of neutropenia or graft-versus-host disease may prevent some fungal infections but increase the risk for others. Detection of fungal antigens in body fluids, including cryptococcus capsular polysaccharide, histoplasma antigen, galactomannan, and β- d -glucan, is viewed as being clinically useful for at least the presumptive diagnosis of invasive fungal infections. β- d -Glucan is an attractive antigen in that it is found in a broad range of fungal agents, including the commonly encountered agents Candida spp., Aspergillus spp., and Pneumocystis jirovecii. Cross-reactions with certain hemodialysis filters, beta-lactam antimicrobials, and immunoglobulins, which raise concerns about false-positive tests, have also been described. As a result, the use of this testing must be closely monitored. In this point-counterpoint, we have asked Elitza Theel, who directs the Infectious Disease Serology Laboratory at the Mayo Clinic, to address why she believes that this test has value in the diagnosis of invasive fungal infections. We have asked Christopher Doern, Director of Clinical Microbiology at Children's Medical Center of Dallas, why he questions the clinical value of β- d -glucan testing.

ABSTRACT An on-plate testing method using formic acid was evaluated on the Bruker Biotyper matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry system using 90 yeast and 78 Corynebacterium species isolates, and 95.6 and 81.1% of yeast and 96.1 and 92.3% of Corynebacterium isolates were correctly identified to the genus and species levels, respectively. The on-plate method using formic acid yielded identification percentages similar to those for the conventional but more laborious tube-based extraction.

ABSTRACT The performance of the Bruker Biotyper matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometer (MS) for the identification of dermatophytes from clinical cultures was compared to that of dermatophyte identification using 28S rRNA gene sequencing. The MALDI Biotyper library (MBL; version 3.0) was used alone and in combination with a supplemented library containing an additional 20 dermatophyte spectra (S-MBL). Acquired spectra were interpreted using both the manufacturer-recommended scores (genus, ≥1.7; species, ≥2.0) and adjusted cutoff values established by this study (genus, ≥1.5; species, ≥1.7); identifications required a minimum 10% difference in scores between the top two different organisms to be considered correct. One hundred well-characterized, archived dermatophyte isolates and 71 fresh dermatophyte cultures were evaluated using both libraries and both sets of cutoff criteria. Collectively, the S-MBL significantly outperformed the MBL at both the genus (93% versus 37.4%; P < 0,0001) and species (59.6% versus 20.5%; P < 0.0001) levels when using the adjusted score criteria. Importantly, application of the lowered cutoff values significantly improved genus ( P = 0.005)- and species ( P < 0.0001)-level identification for the S-MBL, without leading to an increase in misidentifications. MALDI-TOF MS is a cost-effective and rapid alternative to traditional or molecular methods for dermatophyte identification, provided that the reference library is supplemented to sufficiently encompass clinically relevant, intraspecies strain diversity.