Performance of qualitative and quantitative antigen tests for SARS-CoV-2 in early symptomatic patients using saliva

Yokota, I.; Sakurazawa, T.; Sugita, J.; Iwasaki, S.; Yasuda, K.; Yamashita, N.; Fujisawa, S.; Nishida, M.; Konno, S.; Teshima, T.

Background: The rapid detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an urgent need for the prevention and containment of disease outbreaks in communities. Although the gold standard is polymerase chain reaction (PCR), antigen tests such as immunochromatographic assay (ICA) and chemiluminescent enzyme immunoassay (CLEIA) that can yield results within 30 minutes. Methods: We evaluated performance of ICA and CLEIA using 34 frozen PCR-positive specimens (17 saliva and 17 nasopharyngeal swab) and 307 PCR-negative samples. Results: ICA detected SARS-CoV-2 in only 14 (41%) samples, with positivity of 24% in saliva and 59% in NPS. Notably, ICA detected SARS-CoV-2 in 5 (83%) of 6 samples collected within 4 days after symptom onset. CLEIA detected SARS-CoV-2 in 31 (91%) samples, with positivity of 82% in saliva and 100% in NPS. CLEIA was negative in 3 samples with low viral load by PCR. Conclusions: These results suggest that use of ICA should be limited to earlier time after symptom onset and CLEIA is more sensitive and can be used in situations where quick results are required.