2. Epidemiological characteristics
Of the 28 patients with COVID-19, 15 were men (53.6%) and 13 were women (46.1%), with a mean age of 42.6 years (range: 20–73 years). Regarding age groups, 8 patients were in their 50’s (28.6%), 6 patients each were in their 20’s, 30’s, and 40’s (21.4%), and 1 patient each was in their 60’s and 70’s (3.6%). Of the 28 patients, 22 were Korean and 6 were Chinese, of whom 2 were visitors.
Of the 16 index cases imported from abroad (57.1%), 6 contributed to the occurrence of secondary infections in 10 patients in Korea. Of those with secondary infection, 7 were first-generation patients (25.0%) and 3 were second-generation patients (10.7%). In the remaining 2 patients (7.2%), the route of transmission remains under investigation.
The initial symptoms were fever or feeling hot (9 patients, 32.1%), sore throat (9 patients, 32.1%), cough or sputum production (5 patients, 17.9%), chills (5 patients, 17.9%), and muscle ache (4 patients, 14.3%). However, 3 patients were asymptomatic. In 18 patients, pneumonia was confirmed using imaging once hospitalized (64.3%). As of February 14th, 7 out of 28 patients had been discharged, and the average length of hospital stay was 12.7 days (range: 8–19 days).
One patient had visited a marketplace in China, while 2 had visited a medical facility in Wuhan City. Of the 28 patients, 10 (35.7%) had at least 1 underlying disease including hypertension, diabetes, asthma, chronic rhinitis, dyslipidemia, and hypothyroidism, and 1 patient had undergone surgery for lung cancer (Table 1).
“Test count” refers to the number of cases that were reported to KCDC by local health centers and were then tested. Prior to February 7th, tests were conducted by KCDC and the Research Institute of Public Health and Environment in the corresponding cities/provinces, the number of reports and test counts matched. After February 7th, additional tests were conducted for each individual suspected of having COVID-19 increasing the number of reports, aside from those initially conducted by the local health center.
The earliest date of symptom onset among the 25 patients with a clear date of onset, was January 10th (for 3 patients, the date of onset was unclear). Since then, the number of confirmed index cases imported from abroad continued to increase, and symptoms were first confirmed in patients with secondary infection on January 26th. The incubation period was estimated to be 4.1 days based on the date of symptom onset and first exposure (among 9 patients, excluding 1 patient with an unclear date of onset) shown in Figure 1 and Table 2.
In the 16 index cases imported from abroad, the suspected sites where the infection was first contracted were Wuhan, China (11 cases, 68.3%), Singapore (2 cases, 12.5%), Zhuhai, China (1 case, 6.3%), Thailand (1 case, 6.3%), and Japan (1 case, 6.3%). The 10 patients with secondary infection for which the routes of transmission were known were either family members (7 cases, 70.0%) including relatives (2 cases), or acquaintances (3 cases, 30%) of the primary patients. The suspected sites of transmission were the home (7 cases, 70.0%), a restaurant (1 case, 10.0%), a church (1 case, 10.0%), and other locations (1 case, 10.0%).
With regard to the distribution of the 24 cases by region, excluding the 2 Wuhan residents and 2 patients who were evacuated via a charter flight, high incidence rates were reported in Gyeonggi-do (11 patients, 39.3%) and Seoul (9 patients, 32.1%), followed by Gwangju (2 patients, 7.1%), and Jeollabuk-do and Jeollanam-do (1 patient each, 3.6%) shown in Table 2.