ABSTRACT
BACKGROUND: Coronavirus Disease 2019 (COVID-19) has become a worldwide pandemic and affected more than 227 countries or territories, resulting in more than 25 million cases with over 0â¢85 million deaths, as of September 2, 2020. Taiwan has been successful in countering the COVID-19 outbreak, however, the potential risk for asymptomatic infections and the prevalence rates remain unknown. We aimed to estimate the seroprevalence of COVID-19 in Taiwan via serologically testing hospital patients with neither symptoms indicative of nor positive nucleic acid test for SARS-CoV-2 infection. METHODS: Residual specimens from laboratory blood tests for outpatient and emergency department patients visiting a medical centre in Taipei, Taiwan, within one week in May and another in July, 2020, were collected. We used Elecsys Anti-SARS-CoV-2 Assay to screen and further validated cases with high cutoff index by a confirmatory ELISA assay. We also analysed antibody responses against SARS-CoV-2 along disease progression in four nucleic acid test confirmed COVID-19 patients. FINDINGS: Blood samples from a total of 14,765 patients were tested. The unweighted seroprevalence of anti-SARS-CoV-2 antibodies was 0â¢07% [95% CI, 0â¢04%-0â¢13%]; after weighting with the population demographics of Taiwan, the estimated overall seroprevalence was 0â¢05% [95% CI, 0â¢02%-0â¢10%]. Furthermore, based on data of the four COVID-19 cases, the seroconversion dates for IgM were as early as 9 days and that for IgG 11 days after symptoms onset. INTERPRETATION: We screened the anti-SARS-CoV-2 antibodies in a small-scale population-based study and observed an approximately 0â¢05% seroprevalence of COVID-19, indicating that the current containment protocols emphasising mask wearing, hand washing, social distancing and mandatory quarantine for all incomers are effective in Taiwan. FUNDING: Taipei Veterans General Hospital, Taipei, Taiwan.