 We analyzed reports for 59,073 contacts of 5,706 coronavirus disease, COVID-19, index patients reported in South Korea during January 20 to March 27, 2020. Of 10,592 household contacts, 11.8% had COVID-19. Of 48,481 non-household contacts, 1.9% had COVID-19. Use of personal protective measures and social distancing reduces the likelihood of transmission. This article was authored by Young Joon Park, Young Joon Cho, Ok Park, and others.