Abstract
BackgroundCryptococcosis is a major opportunistic invasive mycosis in immunocompromised patients, but it is also increasingly seen in immunocompetent patients. In the early stages of cryptococcosis, limitations of the detection method may hinder the diagnosis. A molecular diagnostic technique based on nucleic acid sequence-based amplification (NASBA) method was developed to fulfil the need for efficient diagnosis of cryptococcosis.MethodsWe compared the diagnostic performance of NASBA, PCR and cryptococcal antigen (CrAg) test (colloidal gold method) in clinical samples from 25 cryptococcosis patients (including 8 cryptococcal meningoencephalitis and 17 pulmonary cryptococcosis) who were categorized as proven cases (n = 10) and probable cases (n = 15) according to the revised EORTC/MSG definitions. 10 patients with non-Cryptococcus infection and 30 healthy individuals were categorized as control group.ResultsThe lowest detection limit of NASBA was 10 CFU/mL, and RNA of non-target bacteria or fungi was not amplified. The sensitivity of NASBA, PCR and colloidal gold method was 92.00% (95% CI 72.50–98.60%), 64.00% (95% CI 42.62–81.29%), 100.00% (95% CI 83.42–100.00%), and the specificity was 95.00% (95% CI 81.79–99.13%), 80.00% (95% CI 63.86–90.39%) and 82.50% (95% CI 66.64–92.11%) respectively. The highest specificity (97.50%), accuracy (95.38%) and k value (0.90) were achieved when both NASBA and colloidal gold results were positive.ConclusionsNASBA is a new alternative detection method for cryptococcosis which is both accurate and rapid without expensive equipment and specialised personnel. It may be used as a tool for confirming current infection as well as monitoring the effectiveness of antifungal treatment. The use of NASBA to detect Cryptococcus RNA in blood samples is of great significance for the diagnosis of pulmonary cryptococcosis. The combination of NASBA and colloidal gold can improve the diagnostic accuracy of cryptococcosis.
Highlights
Cryptococcosis is a major opportunistic invasive mycosis in immunocompromised patients, but it is increasingly seen in immunocompetent patients
Combining the detection results of nucleic acid sequence-based amplification (NASBA), Polymerase Chain Reaction (PCR) and colloidal gold to further explore their diagnostic efficacy for cryptococcosis, we found that when both NASBA and colloidal gold results were positive, the highest specificity, accuracy and k value could be obtained without obvious reduction of sensitivity
The combination of NASBA and colloidal gold can improve the diagnostic accuracy of cryptococcosis as well as achieve a highest agreement with the EORTC/MSG criteria, which is more beneficial to the diagnosis of cryptococcosis
Summary
Cryptococcosis is a major opportunistic invasive mycosis in immunocompromised patients, but it is increasingly seen in immunocompetent patients. The detection of CrAg by colloidal gold method is one of the most helpful fungal routine tests, which is easy to use and has better sensitivity than other conventional methods for rapid diagnosis of early Cryptococcus infection [7, 8]. False-positive as well as false-negative results have been caused because of many factors such as rheumatoid factor, cross antigens of other fungi or bacterial and unknown non-specific proteins. It is unreliable for monitoring the efficacy of antifungal treatment [9, 10]
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