Cryptococcus neoformans meningitis with negative cryptococcal antigen: Evaluation of a new immunochromatographic detection assay

Abstract

Detection of cryptococcal antigen in serum or cerebrospinal fluid allows cryptococcal meningitis diagnosis within few hours with >90% sensitivity. In an HIV-positive patient with Cryptococcus neoformans meningitis, initial antigen detection by immunoagglutination was negative. We thus evaluated a new immunochromatographic detection assay that exhibited a higher sensitivity.

Keywords: Antigen test; Cryptococcus neoformans; HIV; immunochromatography; meningitis.

Fig. 1

Time course of the case study and treatment. The buttom part of the figure shows results of cryptococcal antigen titers and cryptococcal culture. Cryptococcal antigen titers were determined by immunoagglutination (Pastorex) and lateral flow assay (Immunomycologics Inc., IMMY). Quantitative culture was achieved as follows: four drops of 100 μL, 50 μL, and 10 μL were deposited in duplicate on a brain–heart infusion plate supplemented with blood and incubated at 37°C with CO₂. Antifungal and antiretroviral treatment is depicted in the upper part of the figure. Antifungal treatment consisted of liposomal amphotericin B (5 mg/kg) and intravenous flucytosine (25 mg/kg every other day). After 2 weeks of combined therapy, the patient was apyretic and headache disappeared; lumbar puncture revealed normal opening pressure and decreased amount of protein (862 mg/L), and CSF culture was sterile. Cryptococcal antigen detection in the CSF became negative as well. Antifungal treatment was switched to fluconazole (400 mg once daily) and antiretroviral treatment was initiated, without relapse of cryptococcal meningitis.

Fig. 2

Cryptococcus neoformans infection over 18 years. (A) Total number of cryptococcal antigen detection by immunoagglutination and number of positive results in our hospital from 1996 to 2014. Results were obtained with the Bio-Rad assay Pastorex Crypto Plus 61747. (B) Evolution of cryptococcal antigen titer among positive results: comparison between 1996–2004 and 2005–2013 (comparison by Mann-Whitney test). Antigen titer for positive samples was determined by serial dilution according to the manufacturer's procedure.

Fig. 3

Evaluation of the lateral flow assay (LFA) detection system from Immunomycologics Inc. (IMMY). A total of 50 samples (30 positive and 20 negative) previously analysed with the immunoagglutination assay Pastorex Crypto Plus 61747 (Bio-Rad) were retrospectively tested with the IMMY-LFA (Supplementary Table 1). The 20 samples that were negative with the Pastorex assay also came negative with the LFA assay (data not presented). In 9 cases, immunochromatography was performed but the titration could not be done because the volume of stored CSF was not sufficient. Antigen titers were always higher with the IMMY-LFA system than with the Pastorex assay (comparison by Wilcoxon signed rank test).