In South Korea, the first cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were identified in January 2020. By April 2020, the number of coronavirus disease (COVID-19) cases went up to 10,683 infections, and 237 people had died of the disease.
A large percentage of the cases and deaths were a result of superspreader events in the Daegu-Gyeongsangbuk province. At the start of the outbreak, public health authorities raised the infectious disease alert to 3, the highest level in South Korea. Subsequently, increased screening and testing through drive-through screening centers and COVID-19 testing facilities at private hospitals were implemented. In April 2020, social distancing measures implemented in March were relaxed as the COVID-19 epidemic in South Korea had come under control.
Although some studies examined how public health interventions can help contain COVID-19 outbreaks, not much information was available on public health measures against SARS-CoV-2 transmission, specifically in South Korea.
Analyzing COVID-19 transmission outside the Daegu-Gyeongsangbuk province
Researchers from the Konyang University College of Medicine, South Korea, and The University of Hong Kong, Hong Kong, analyzed the transmission of COVID-19 outside of the Daegu-Gyeongsangbuk provincial region in South Korea, in a recent study published in the CDC’s Emerging Infectious Diseases journal.
The team estimated the transmissibility of the SARS-CoV-2 virus and determined the impact of public health measures implemented outside the Daegu-Gyeongsangbuk province in South Korea. The researchers collected local health data from the city or provincial public health departments. Gathered data included the source of infection, the date of exposure, and date of onset of illness along with contact history and age and sex of patients. Their analysis was restricted to regions in South Korea outside the Daegu-Gyeongsangbuk provincial region. Over the 3-month study period - January 20 to April 21, 2020 - data for 2,023 cases were collected, which covered about 98% of the 2,066 cases reported by the South Korea Ministry of Health and Welfare.
They analyzed the time between the onset of illness and lab confirmation for 818 symptomatic case-patients. Data for 181 patients, whose precise contact history with other confirmed cases were known, were analyzed so as to estimate the incubation period. They identified 44 infection clusters and 79 case-patients who were exposed to only 1 index case-patient among the clusters.
To determine the effectiveness of non-pharmaceutical interventions used in South Korea, the team estimated a real-time measure of transmission intensity, the instantaneous effective reproduction number (Rt), from daily onset of cases, and their estimated serial interval distribution. Daily Rt estimates were presented from February 16, 2020, as stable estimates of Rt were not available owing to low number of confirmed cases.
Non-pharmaceutical measures reduced transmission without lockdown
A combination of non-pharmaceutical interventions, such as improved screening, quarantine of suspected and confirmed cases, and social distancing measures, were enforced in South Korea over time. The results of the study suggest that these interventions, even in the absence of a lockdown, helped reduce the transmissibility of SARS-CoV-2 outside the Daegu-Gyeongsangbuk provincial region.
The findings suggest that non-pharmaceutical interventions used in South Korea during the early phase of the COVID-19 outbreak reduced virus transmissibility contained the spread of the virus in the local community. They estimated that non-pharmaceutical measures reduced transmission by about 34% without imposing a strict lockdown in the province. They also found that in order to optimize epidemic control, continuous efforts are needed to monitor the transmissibility of COVID19. The researchers, however, warn that South Korea could still be susceptible to further epidemic waves or outbreaks.
Since the infection can still be imported from overseas by travelers, ongoing monitoring of the reproductive number is required to gather relevant data that will help policymakers implement measures to control a potential second wave of COVID-19 in South Korea.
“Our results suggest that those interventions, without a lockdown, reduced the transmissibility of SARS-CoV-2 in regions outside of the Daegu-Gyeongsangbuk provincial region, in South Korea.”
Limitations of the study
The study also has some limitations. Large clusters reported as superspreaders were not included in the analysis of SARS-CoV-2 transmissibility changes. Also, there may be undetected cases that were not part of the study, which could mislead the actual trends of infections in the specific population. The estimations in the study were based on self-reported data, which are prone to reporting bias. Since government-generated data were not available, they used data from online case reports, which might have caused inaccuracies in the information used in the analyses.
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