Based on the surveillance data, we report the basic epidemiological characteristics of COVID-19 to examine the early course of the pandemic. Furthermore, factors associated with COVID-19 cases and fatality were investigated to provide information on a vulnerable part of the population to guide public health prioritization.

Only a few weeks after the first case of coronavirus disease 2019 (COVID-19) was reported in Wuhan, China, the first case of COVID-19 was confirmed in the Republic of Korea on January 20, 2020 [ 1 ]. International travel has facilitated the spread of COVID-19 throughout the world. As of March 13, 2020, 118 countries, territories, and areas have reported COVID-19 cases, however, differences in patterns and intensity of transmission ranges were observed [ 2 ]. In February and early March in Korea, a sharp increase in the number of COVID-19 cases were observed, with most infections in specific clusters and geographical regions.

This is a summary of the first 7,755 patients with confirmed COVID-19 in Korea as of March 12, 2020. To obtain demographic, epidemiological, and early clinical information, COVID-19 reporting and surveillance data were retrieved from Korea Centers for Disease Control and Prevention (KCDC)-operated National Notifiable Disease Surveillance System (NNDSS) [ 3 ]. The patient age was provided on the date of diagnosis, and key indicators such as estimated duration of exposure, date of onset of symptoms, and route of transmission were identified by field epidemiological investigators [ 1 ]. It must be noted that the data presented in this summary may change depending on the results of further epidemiological investigations.

There were 66 laboratory-confirmed fatal cases of COVID-19, as of March 12, 2020 ( Table 3 ). The median age was 77 years (range, 35-93 years), and female-to-male ratio of 44:56. Of 63 cases, 96.8% were reported to have comorbidities: 47.6% hypertension, 36.5% diabetes, 16% neurodegenerative disorders, and 17.5% pulmonary diseases. There were 71.2% of fatal cases in Daegu and 24.2% were from Gyeongbuk. There were 5 patients who succumbed to death at home, and COVID-19 was identified as the cause of death in 11 individuals after their death. The median interval between onset of symptoms and death was 10 days (range 1-24 days), while the median interval between date of hospitalization and date of death was 5 days (range 0-16 days).

Fatal cases of COVID-19 in Korea, as of March 12, 2020 are shown in Tables 2 and 3 . Case fatality proportion was the highest among people aged ≥ 80 years in Daegu, followed by those aged 70-79 years in Daegu, and elderly persons ≥ 80 years old in Gyeongbuk. Overall case fatality proportion in Daegu and Gyeongbuk were 0.8% and 1.4%, which were higher than that in other regions with 0.4%. Figure 4 depicts age-specific epidemic curve stratified as 0-59 years and ≥ 60 years. The outbreak generally began with the younger age group, followed by the elderly population.

The epidemic curves presented in Figures 1 and 2 were generated using National Notifiable Disease Surveillance System (NNDSS) data. Epidemic curves by date of onset preceded epidemic curves by date of diagnosis, by a few days or a week ( Figure 1 ). It must be noted that the date of symptom onset may change depending on further epidemiological investigation, and delayed reporting of cases. Figure 2 depicts an epidemic curve by different regions of Korea: the nationwide, Daegu, Gyeongbuk, and others (outside Daegu and Gyeongbuk). From mid-February, an increased number of cases were reported with a peak in late February and early March. Figure 3 shows the age distribution and sex ratio among Daegu, Gyeongbuk, and others regions. Note the increased proportion of cases in 20-29 years and in females among cases in Daegu and Gyeongbuk.

As of March 12, 2020, a total of 7,755 laboratory-confirmed cases of COVID-19 and 66 deaths were recorded in Korea, giving a case fatality proportion of 0.9% ( Table 1 ). The female-to-male ratio of confirmed COVID-19 cases was 62:38. The age group 20-29 years accounted for the highest level of all confirmed cases at 28.9%, followed by 50-59 years, and 40-49 years. The case fatality proportion was 0.1% among 30-39 years and 40-49 years age groups, then increased to 0.4% in the 50-59 years, 1.5% in the 60-69 years, 5.0% in the 70-79 years, and 8.5% in the ≥80 years age groups ( Table 1 ).

Discussion

The analysis of the first 7,755 cases of COVID-19 in Korea showed an initial increase in cases in specific geographical regions, comparable to the epidemiological situation in China and Italy [ 4 5 ]. In Korea, despite a sharp decline in the number of confirmed cases reported, there were still a relevant number of confirmed cases per week in late February and early March. With descriptive analysis of interim surveillance data, the data suggest that the patient outcome differed markedly between the geographic regions, highlighting the magnitude of surge of cases and access to hospitalization. The difference in age distribution of COVID-19 cases compared with China may reflect active surveillance of a cluster of religious groups tied to the outbreak.

A summary of the epidemiological characteristics of the first 7,755 COVID-19 cases in Korea confirms the contagiousness of COVID-19 that led to a nationwide outbreak in a few weeks. Triaging patients for hospitalization, social distancing (to reduce the number of contacts), and reporting the outbreak amongst vulnerable people in the population may have played a role in the recent decline in cases of COVID-19. However, in the initial response to COVID-19, quarantine, early detection, and isolation of suspected cases of COVID-19, may have contributed to lowering the wave of this epidemic in other parts of Korea. More severe cases were reported in the elderly with existing comorbidities, which warrants clear triage management and a high-risk approach in healthcare access prioritization. COVID-19 does not appear to be fatal among young adults and children, however their role in disease transmission should be further assessed.

This summary may help in the understanding of early phase disease dynamics for the COVID-19 outbreak, and guide future public health measures in other countries.