Mayor Muriel Bowser said Monday that she is also placing local National Guard units on standby, but not actively deploying them yet. She said she envisions the National Guard playing a role in organizing mass virus testing sites in the future.

"There is of course a lot more that we need to learn about COVID-19, but one thing we do know is that social distancing can mitigate the spread of the virus," Bowser said at a press conference. "At the moment, social distancing is our main tool."

All restaurants and bars will be able to offer to offer carry-out to customers or to food delivery services, but all dining or drinking in the establishments is prohibited, starting at 10 p.m. Monday.

The order represents one of the final available steps for Bowser's government, short of simply closing all restaurants and bars. It also reflects the sheer speed with which public alarm over the virus has taken over daily life in the America.

Less than a week ago — on March 11, when Bowser declared a state of emergency — her government was recommending that all public gatherings of more than 1,000 people be postponed. Within days, that maximum number had been revised down to 250 people, and restaurants were told to function normally but to ban should-to-shoulder bar seating and not to use any attached banquet rooms. Now the government has concluded that just about any size of public gathering is too large.

"We want to be as responsive of a community as we can in the U.S. to help be on the forefront of flattening the curve and helping to end this pandemic," said Dr. LaQuandra Nesbitt, director of the District of Columbia's Department of Health.

Bowser warned against restaurants or bars attempting to flout the new rules, and encouraged residents to report any transgressions.

"As mayor, I don't wake up in the morning thinking about how I can shut down a business or order a fine," she said Monday, "But I'll do it."

For most people, the new coronavirus causes only mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia. The vast majority of people recover from the new virus.

Washington, D.C., reported five new cases of coronavirus infection Monday, bringing its official total up to 22. But that tally doesn't include people who may have been infected in Washington but live in nearby northern Virginia or southern Maryland.

The virus has devastated what would normally be the start of Washington's high season for tourists and school trips. The popular Cherry Blossom Festival, which was supposed to start Friday, March 20, has been largely cancelled, tours of the White House and Capitol suspended, and the National Zoo, Kennedy Center and the entire Smithsonian network of museums shut down.