Evaluation of a commercial IgG monotest assay: a new automated chemiluminescent immunoassay for the serodiagnosis of cystic echinococcosis

Background: Cystic echinococcosis (CE) is a zoonotic disease caused by the tapeworm Echinococcus granulosus complex. The geographical distribution is worldwide with variable incidences. In Belgium, only few imported cases are reported each year. Serodiagnosis of CE is performed by using a combination of immunoassays which are mainly based on crude hydatid antigens. The Belgian National Reference Laboratory, has evaluated the CE-IVD Hydatidosis VirClia® IgG chemiluminescent immunoassay and compared it with two other immunoassays. Methods: A total of 79 sera were retrospectively included from 15 patients with CE, 29 with alveolar echinococcosis, 16 with toxocariasis and 19 negative controls. Three immunoassays were compared: the Hydatidosis VirClia® IgG monotest assay which was run on the Virclia® Lotus (Vircell, Spain); the Ridascreen® Echinococcus IgG assay (R-Biopharm, Germany) and the Bordier® Echinococcus granulosus IgG ELISA (Bordier, Switzerland), which were tested on the ETI-Max 3000 immunoassay analyzer (DiaSorin, Italy). The McNemar test is used for statistical analysis. Results: All three methods showed 100% sensitivity. Regarding specificity, the Ridascreen® (78.1%) and VirClia® (76.6%) assays showed comparable performance (p-value: 1), while the Bordier® assay had poor results (54,7%) (p-value: 0,0007). The Bordier® assay showed 76% cross-reactions with E. multilocularis (22/29) and 31% with Toxocara sp. (5/16), while the VirClia® assay showed 51,7% (15/29) and no cross-reaction with Toxocara antigens. For Ridascreen® assay, 34% and 19% cross-reactions were observed for E. multilocularis (10/29) and Toxocara sp. (3/16), respectively. Non-specific reactions in negative controls were only observed with the Ridascreen® (1/19) and Bordier® assays (2/19). The shortest turnaround time was observed with Virclia® Lotus: 1 hour versus 3 hours for two other assays. Conclusions: All assays showed very high sensitivity. However, regarding specificity, the VirClia® performs better than the Bordier® and similarly to the Ridascreen® assay. Besides, the ready-to-use monotest format offers many advantages such as a quicker methodology and a reduced workflow. Therefore, the VirClia® assay is an efficient screening method for the detection of CE but should always be combined with an immunoblot assay to assess the specificity