RESULTS
This study included data collected from 274 patients from Severance Hospital and 1,833 patients from 55 other hospitals across South Korea (Figure 1). The 55 hospitals included 19 in Seoul, 12 in Gyeonggi-province, 4 in Incheon, 2 in Daejeon, 2 in Daegu, 2 in Busan, 2 in Gwangju, 3 in Gangwon-province, 2 in Gyeongsangbuk-province, and 3 each in Chungcheongnam-province, Gyeongsangnam-province, Jeollabuk-province, and Jeollanam-province. A total of 2,360 samples were collected, including 253 follow-up samples.