 The COVID-19 outbreak in a South Korean call center resulted in 8.5% of the tested individuals having confirmed cases with an attack rate of 43.5% among employees working on the 11th floor. Of the symptomatic case patients, the household secondary attack rate was 16.2%. Only 1.9% of the confirmed COVID-19 cases remain asymptomatic and none of their household contacts acquired secondary infections. Effective measures for containing rapid outbreaks in crowded work settings include extensive contact tracing, testing all contacts, and early quarantine. This article was authored by Shin Young Park, Young Man King, Seonju Lee, and others.