In Britain, where four more cases linked to a cluster of transmissions at a ski resort in France were confirmed, the health authorities on Monday declared the virus an “imminent threat” to public health and announced new measures to combat its spread. That includes the ability to forcibly quarantine people — a sign of how seriously they are treating the outbreak.

Related: Sixty-five new cases were confirmed on a cruise ship quarantined in Yokohama, Japan, bringing the total on board to 135.

Quote of note: “Let’s not shake hands in this special time,” said China’s leader, Xi Jinping, as he reappeared in public in Beijing on Monday. The visit came after Mr. Xi had been criticized for appearing aloof amid increasing public discontent with his government’s response to the crisis and an idled economy.

Go deeper: In our Opinion section, an epidemiologist heading to the W.H.O. meeting today lists what is known, and not yet known, about the virus.