A study released by The Centers for Disease Control and Prevention on Wednesday reveals that 6.4 percent of the novel coronavirus cases in Singapore between January 23 and March 16 were contracted from people who were infected with the virus but were not showing symptoms. The agency studied 157 “locally acquired cases” of the total 243 cases in the country during that time period and focused on seven “clusters of cases in which presymptomatic transmission” likely caused a second round of infections. The findings, which lay bare the evidence that carriers of the disease can unknowingly infect others, emphasize “the critical role social distancing, including avoidance of congregate settings, plays in controlling the COVID-19 pandemic,” the report reads. It also urges public health officials to “strongly consider including a period before symptom onset to account for the possibility of presymptomatic transmission.”

Dr. Adrian Hyzler, the chief medical officer for Healix International, said “the biggest danger here is that this is like a stealth attack in that you have no idea that the person you have come into contact with is contagious,” The Daily Beast previously reported. Chinese government data revealed that these “silent carriers” could account for one-third of China’s nationwide cases, the South China Morning Post reported.