ABSTRACT
Objectives: After the third wave of coronavirus disease (COVID-19), by mid-February 2021, approximately 0.16% of the population was confirmed positive, which appeared to be one of the lowest rates worldwide at that time. However, asymptomatic transmission poses a challenge for COVID-19 surveillance. Therefore, a community-based serosurvey of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was conducted to understand the effectiveness of Korea's strong containment strategy. Methods: We collected 5,002 residual sera samples from January 30 to March 3, 2021 from 265 medical facilities in Seoul, 346 in Kyunggi-do' and 57 in Incheon. Among them, 60 samples from tertiary institutions were excluded. We defined the sub-regions according to the addresses of the medical facilities where the specimens were collected. Elecsys Anti-SARS-CoV-2 was used for the screening test, and positivity was confirmed using the SARS-CoV-2 sVNT Kit. Prevalence was estimated using sampling weight and the Wilson score interval for a binomial proportion with a 95% confidence interval. Results: Among the 4,942 specimens, 32 and 25 tested positive for COVID-19 in the screening and confirmatory tests, respectively. The overall crude prevalence of SARS-CoV-2 antibody was 0.51%. The population-adjusted overall prevalence was 0.55% in women and 0.38% in men. The region-specific estimation was 0.67% and 0.30% in Gyeonggi-do and Seoul, respectively. No positive cases were detected in Incheon. Conclusion: The proportion of undetected cases in South Korea remains low. Therefore, an infection control strategy with exhaustive tracing and widespread pre-emptive testing appears to be effective in containing the spread of the virus in the community.
ABSTRACT
BACKGROUND: Seroprevalence studies of coronavirus disease 2019 (COVID-19) cases, including asymptomatic and past infections, are important to estimate the scale of the disease outbreak and to establish quarantine measures. We evaluated the clinical performance of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody assays available in Korea for use in seroprevalence studies. METHODS: The sensitivity, specificity, cross-reactivity, and interference of five SARS-CoV-2 antibody assays were evaluated using the following: 398 serum samples from confirmed COVID-19 patients, 510 negative control samples from before 2018 (pre-pandemic), 163 serum samples from patients with SARS, Middle East respiratory syndrome (MERS), and other viral infections, and five samples for the interference study. RESULTS: The sensitivities of the five assays ranged from 92.2% to 98%, and their specificities, including cross-reactivity and interference, ranged from 97.5% to 100%. The agreement rates were excellent (kappa >0.9). Adjustment of the cutoff values could be considered through ROC curve analysis. The positive predictive values of the individual assays varied from 3.5% to 100% at a 0.1% prevalence but were as high as ≥95% when two assays were combined. CONCLUSIONS: The prevalence of COVID-19 in Korea is considered to be exceptionally low at present; thus, we recommend using a combination of two or more SARS-CoV-2 antibody assays rather than a single assay. These results could help select SARS-CoV-2 antibody assays for COVID-19 seroprevalence studies in Korea.