The evaluation of a novel digital immunochromatographic assay with silver amplification to detect SARS-CoV-2

Kurihara, Y.; Kiyasu, Y.; Akashi, Y.; Takeuchi, Y.; Narahara, K.; Mori, S.; Takeshige, T.; Notake, S.; Ueda, A.; Nakamura, K.; Ishikawa, H.; Suzuki, H.

Introduction Rapid antigen tests are convenient for diagnosing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); however, they have lower sensitivities than nucleic acid amplification tests. In this study, we evaluated the diagnostic performance of Quick Chaser Auto SARS-CoV-2, a novel digital immunochromatographic assay that is expected to have higher sensitivity than conventional antigen tests. Methods A prospective observational study was conducted between February 8 and March 24, 2021. We simultaneously obtained two nasopharyngeal samples, one for evaluation with the QuickChaser Auto SARS-CoV-2 antigen test and the other for assessment with reverse transcription PCR (RT-PCR), considered the gold-standard reference test. The limit of detection (LOD) of the new antigen test was compared with those of four other commercially available rapid antigen tests. Results A total of 1401 samples were analyzed. SARS-CoV-2 was detected by reference RT-PCR in 83 (5.9%) samples, of which 36 (43.4%) were collected from symptomatic patients. The sensitivity, specificity, positive predictive value, and negative predictive value were 74.7% (95% confidence interval (CI): 64.0-83.6%), 99.8% (95% CI: 99.5-100%), 96.9% (95% CI: 89.2-99.6%), and 98.4% (95% CI: 97.6-99.0%), respectively. When limited to samples with a cycle threshold (Ct) <30 or those from symptomatic patients, the sensitivity increased to 98.3% and 88.9%, respectively. The QuickChaser Auto SARS-CoV-2 detected 34-120 copies/test, which indicated greater sensitivity than the other rapid antigen tests. Conclusions QuickChaser Auto SARS-CoV-2 showed sufficient sensitivity and specificity in clinical samples of symptomatic patients. The sensitivity was comparable to RT-PCR in samples with Ct<30.