Three clusters of COVID-19, a Chinese tour group, a company conference and a church, were studied on the transmission of this disease in Singapore. The findings mainly showed that human-to-human direct or prolonged close contact was common in affected patients. Incubation period ranged from 3 to 8 days with a median incubation period of 4 days. The study recommended improvements in detection of COVID-19 through both active and passive surveillance.