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 may 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 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