Time-dependent changes in the seroprevalence of COVID-19 in asymptomatic liver disease outpatients in an area in Japan undergoing a second wave of COVID-19.

AIM: Coronavirus disease 2019 (COVID-19) is a serious public health concern, with unclarified prevalence in Japan. Concomitant liver disease could increase the severity of COVID-19 disease, and chronic liver disease patients sometimes require frequent admission and gastrointestinal endoscopy. Thus, clarifying the prevalence of asymptomatic COVID-19 in outpatients with liver disease is essential for preventing nosocomial infections. We aimed to clarify the time-dependent changes in COVID-19 seroprevalence in liver disease outpatients, who were asymptomatic for COVID-19, in an area of Japan experiencing a second wave of COVID-19. METHODS: We included the preserved sera of 100, 300, and 300 consecutive liver disease outpatients, who were asymptomatic for COVID-19, from May 2019, March 2020, and May 2020, respectively. The sera were analyzed immunochromatographically to detect immunoglobulin G against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (KURABO) and by Elecsys Anti-SARS-CoV-2-assay (Roche Diagnostics). RESULTS: Analysis of 100 cases from May 2019, before COVID-19 became pandemic, revealed that the specificity of immunochromatographic tests and Elecsys were 98% (95% confidence interval [CI], 93-99.8%) and 100% (95% CI, 97-100%), respectively. Analysis of 300 cases from March 2020 revealed a seroprevalence of 0.3% (1/300; 95% CI, 0-1.8%) for COVID-19 by Elecsys Anti-SARS-CoV-2 assay. Analysis of 300 cases from May 2020 revealed a seroprevalence of 0% (0/300; 95% CI, 0-1.0%). CONCLUSIONS: The Elecsys Anti-SARS-CoV-2 assay has high specificity. The cumulative seroprevalence of COVID-19 by the Elecsys Anti-SARS-CoV-2 assay in outpatients with liver disease in Sapporo, who were asymptomatic for COVID-19, was 0.17% (1/600; 95% CI, 0.0-0.9%) until May 2020.