However, there is a lack of study to assess the changes of this active case finding strategy specifically. Increase of the cases can be observed by the changes of public health efforts of extensive COVID-19 case finding and contact tracing. Sustained increases in cases were observed as the strict social distancing measures were further relaxed by opening public facilities on when the first epidemic wave had already ended. These strict social distancing measures were relaxed on 20 April 2020, because the daily reported number of cases was under 50 and the unknown origin of infection was less than 5% among total cases of investigation for the previous 2 weeks. Between 22 March and 19 April 2020, strict social distancing measures included recommendations to the public to stay at home and to delay or cancel social gatherings, as well as policies including closing schools and other public facilities, allowing greater flexibility in sick leave, and encouraging work-from-home and flexible working hours. Furthermore, combined public health measures including travel-related measures, case-based measures, and community measures were implemented across South Korea which helped control the first epidemic wave without a complete lockdown (Table S 1). Since the first COVID-19 case was identified in South Korea, isolation of confirmed cases, contact tracing, extensive testing, and timely quarantine of all contacts have been conducted under the strategic guidelines for COVID-19 control from Korea Centers for Disease Control and Prevention (KCDC). Further spread of COVID-19 in the community was reported in mid-February, and the Korean Ministry of Health and Welfare declared the highest level of public health alert on 23 February 2020. South Korea became the third country to report an imported COVID-19 case on 19 January 2020. It was first reported in December 2019 in Wuhan, China, and the World Health Organization declared it a public health emergency of international concern on 30 January 2020. Along with social distancing measures, the enhanced contact tracing including asymptomatic cases could be an efficient approach to control further epidemic waves.Ĭoronavirus disease 2019 (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Our study shows that relaxing social distancing measures was associated with increased SARS-CoV-2 transmission despite rigorous case findings in South Korea. The proportion of asymptomatic cases at presentation increased from 22% (in the first wave) to 27% (in the second wave), while the cases with unknown sources of infection were similar in both waves (22 and 25%, respectively).
#Waves 9 serial numer serial#
Furthermore, children were rarely infectors or infectees, and the mean serial intervals were similar (~ 3 days) in both waves. In both epidemic waves, the most frequent cluster types were religious-related activities and transmissions among the same age were more common.
![waves 9 serial numer waves 9 serial numer](https://www.mdpi.com/jmse/jmse-08-00063/article_deploy/html/images/jmse-08-00063-g009.png)
In early May 2020, within 2-weeks of a relaxation in strict social distancing measures, R t increased rapidly from 0.2 to 1.8 within a week and was around 1 until early July 2020. The proportion of asymptomatic cases and cases with unknown sources of infection were also estimated to assess the changes of infections identified as cases in each wave. Furthermore, to identify the characteristics of each epidemic wave, frequencies of cluster types were measured, and age-specific transmission probability matrices and serial intervals were estimated. To identify changes in the transmissibility of SARS-CoV-2, the daily effective reproductive number ( R t) was estimated using the illness onset of the cases. We collected data on COVID-19 cases published by local public health authorities in South Korea and divided the study into two epidemic periods (19 January–19 April 2020 for the first epidemic wave and 20 April–11 August 2020 for the second epidemic wave). In this study, we aimed to identify the transmission dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections and assess the impact of COVID-19 case finding and contact tracing in each epidemic wave. After relaxing social distancing measures, South Korea experienced a resurgent second epidemic wave of coronavirus disease 2019 (COVID-19).