Utility of the antigen test for coronavirus disease 2019: Factors influencing the prediction of the possibility of disease transmission

Yamamoto, Kei; Suzuki, Michiyo; Yamada, Gen; Sudo, Tsutomu; Nomoto, Hidetoshi; Kinoshita, Noriko; Nakamura, Keiji; Tsujimoto, Yoshie; Kusaba, Yusaku; Morita, Chie; Moriya, Ataru; Maeda, Kenji; Yagi, Shintaro; Kimura, Motoi; Ohmagari, Norio

Objectives Rapid antigen test (RAT) for coronavirus disease 2019 (COVID-19) has lower sensitivity but high accuracy during early-stage compared to reverse transcription-quantitative polymerase chain reaction (RT-qPCR). We aimed to investigate the concordance between the RAT and RT-qPCR results, and their prediction of disease transmission. Methods This single-center retrospective observational study conducted from March 6 to June 14, 2020, included COVID-19 inpatients. We used nasopharyngeal swabs to perform RAT and RT-qPCR. The primary endpoint was concordance between RAT and RT-qPCR results. The secondary endpoints were the factors causing result disagreement and estimated transmissibility in RT-qPCR positive cases with mild symptoms. Results Overall, 229 viral transport media (VTM) samples were obtained from 105 patients. The positive and negative concordance rates for VTM were 41% vs. 99% (κ 0.37) and 72% vs. 100% (κ 0.50) for samples collected on disease days 2-9. Body temperature increase (odds ratio [OR]: 0.54) and absence of drugs with potential antiviral effect (OR: 0.48) yielded conflicting results. RAT was associated with the ability to end isolation (OR: 0.11; 95% confidence interval: 0.20-0.61). Conclusions The RAT and RT-qPCR results were highly consistent for samples collected at the appropriate time and could be useful for inferring the possibility of transmissibility.