Traditional methods for the serologic diagnosis of histoplasmosis include CF and ID. Whereas the CF test is more sensitive than ID, ID is more specific. Hence, these tests are performed in parallel despite their time-consuming and labor-intensive nature. Results may be subject to interpretation, especially when only a single clinical specimen is available for testing. A prototype indirect ELISA (Focus Technologies, Cypress, CA) was evaluated and compared to CF and ID for rapidity and ease of performance using serum specimens obtained from an outbreak of community-acquired histoplasmosis and appropriate controls (n=159). A positive case was defined by the presence of an H and/or M band by ID and a titer of >1:32 by CF. Negative controls included cases of blastomycosis (n=36), coccidioidomycosis (n=10), paracoccidioidomycosis (n=9), aspergillosis (n=2), candidiasis (n=1), sporotrichosis (n=1), and sera negative for the endemic mycoses by CF and ID (n=4). The ELISA used an indirect detection format employing horseradish peroxidase-labeled, anti-human IgG to detect patient antibodies captured onto an antigen-coated microtiter plate. Colorimetric substrate was used and plates were read spectrophotometrically. Mean absorbance units were divided by an absorbance value of 0.8 times the mean plate calibrator (included in the test kit) to calculate the mean index value. The manufacturer’s recommended cutoff for positive, negative, and equivocal ELISA results were any index value that was > 1.1, 0.9 instead of >1.1, test sensitivity, positive predictive value, and efficiency increased to 87%, 87%, and 90%, respectively, with no reduction in specificity or negative predictive value. In conclusion, the ELISA: 1) had good specificity and adequate sensitivity, especially when a positive cutoff value of >0.9 was employed; 2) demonstrated excellent run-to-run reproducibility; 3) was easy to perform; and 4) could be conducted within 4 h needing only a standard microtiter plate reader for data acquisition. Use of commercial sources is for identification purposes only and does not imply endorsement by the U.S. Department of Health and Human Services or CDC.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)