The World Health Organization (WHO) recently said that the corona19 group infection in Beijing, China, is a "critical event" and needs further investigation.

"We have been concerned that there have been no reports of regional infections in the past 50 days, but we are concerned that a group infection has occurred," said Michael Ryan, WHO Deputy Director of Emergency Response.

In particular, Beijing said it is concerned because it is a large city and a well-connected city.