Comparison of Automated SARS-CoV-2 Antigen Test for COVID-19 Infection with Quantitative RT-PCR using 313 Nasopharyngeal Swabs Including from 7 Serially Followed Patients

Hirotsu, Yosuke; Maejima, Makoto; Shibusawa, Masahiro; Nagakubo, Yuki; Hosaka, Kazuhiro; Amemiya, Kenji; Sueki, Hitomi; Hayakawa, Miyoko; Mochizuki, Hitoshi; Tsutsui, Toshiharu; Kakizaki, Yumiko; Miyashita, Yoshihiro; Yagi, Shintaro; Kojima, Satoshi; Omata, Masao

Abstract Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is determined by reverse-transcription PCR (RT-PCR) in routine clinical practice. In the current pandemic situation, a more rapid and high-throughput method is in growing demand. Here, we validated the performance of a new antigen test (LUMIPULSE) based on the chemiluminescence enzyme immunoassay. A total of 313 nasopharyngeal swabs (82 serial samples from 7 infected patients, 231 individual samples from 4 infected patients and 215 non-infected individuals) were analyzed for SARS-CoV-2 by quantitative RT-PCR (RT-qPCR) and then subjected to LUMIPULSE. We determined the cutoff value for antigen detection using receiver operating characteristic curve analysis and compared the antigen test performance with that of RT-qPCR. Further, we compared the viral loads and antigen levels in serial samples from seven infected patients. When using RT-qPCR as the reference, the antigen test exhibited 55.2% sensitivity and 99.6% specificity with a 91.4% overall agreement rate (286/313). In specimens with > 100 viral copies and between 10 and 100 copies, the antigen test showed 100% and 85% concordance with RT-qPCR, respectively. This concordance declined with lower viral loads. In the serially followed patients, the antigen levels showed a steady decline along with viral clearance. This gradual decline was in contrast with the abrupt “positive-to-negative” and “negative-to-positive” status changes observed with RT-qPCR, particularly in the late phase of infection. In summary, the LUMIPULSE antigen test can rapidly identify SARS-CoV-2-infected individuals with moderate to high viral loads and may be helpful for monitoring viral clearance in hospitalized patients.