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The tally of novel coronavirus cases in the Washington region climbed past 1,000 Wednesday as Maryland, Virginia and the District reported their largest single-day increases — a grim markerthat illustrates both the continued spread of the virus and the fact that more testing is being done to detect it.

Maryland announced 74 additional cases, bringing the state’s total to 424, and extended its closure of public schools another four weeks, through April 24. Virginia reported 101 additional cases, for a total of 392. The District reported 48 new cases Wednesday, including an eight-week-old infant, for a total caseload of 235.

D.C. Jail officials said early Thursday that an inmate had tested positive for the virus.

Overall, the region had 1,051 reported cases as of Wednesday evening, with 20 deaths.

“It’s clear that we’ve got community spread now; that is quite obvious,” said Virginia Gov. Ralph Northam (D), a physician by training who on Wednesday directed hospitals to stop performing elective surgeries so that supplies of masks, gloves and other personal protective equipment are not depleted.

“We are just at the beginning of this. We are not at the middle,” Northam said. “We are talking about months, and we are going to see these numbers, unfortunately, continue to rise.”

The 1,000-case milestone for the Washington region happened as the nation and countries around the world continued to battle a pandemic that has caused more than 21,000 deaths. New York, the hardest-hit state, reported an additional 5,000 cases, and New York City’s public hospital system said 13 people died of the virus at one hospital in Queens during a 24-hour period.

Among other developments, Prince Charles, heir to Britain’s throne, was reported to have tested positive for the virus and was isolated with his wife, Camilla, prompting tens of thousands of people to donate blood or volunteer in other ways; New York and other states urged the Trump administration to set up emergency morgues; and unemployment claims filed in California this month reached 1 million.

Both Minnesota and Idaho issued two-week “stay at home” orders that will take effect late Friday night, and Canada said all travelers returning to the county must be quarantined for 14 days unless they are classified as essential workers.

In Maryland, Gov. Larry Hogan (R) attributed much of the spike in cases to an expansion of testing over the past two weeks, with results often taking several days to be reported. But he, too, said the stringent social-distancing measures now in place throughout the Washington region will take considerable time to bear fruit.

“None of us can say in four weeks everything is going to be great and it’s going to be safe for all kids to go back to school,” Hogan said after the school closure was extended. “It would be wonderful if we get to the point where we bend the curve, and we can, but obviously we’re not going to send kids back if we’re still climbing and people are getting infected.”

Northam has closed Virginia schools through the end of the school year, while D.C. Mayor Muriel E. Bowser (D) shut them down through at least late next month. The city has ordered a shutdown of all nonessential businesses as of 10 p.m. Wednesday, and the D.C. government sent an emergency alert to all mobile phones in the city at 8 p.m. to remind residents of the order and urge them to stay at home.

Bowser said the city is not issuing a stay-at-home directive and residents can still leave their homes for “essential trips.” At a town hall, she said city officials will not stop people walking down the street but may ask groups such as people playing basketball or soccer to disperse.

Health experts said signs that the virus is spreading in the region include clusters of infections reported inside long-term-care facilities, communities and religious institutions.

Three former residents of Canterbury Rehabilitation & Healthcare Center outside Richmond, for example, have died of covid-19, the disease caused by the novel coronavirus. One of the deaths was announced Wednesday; two others were reported Tuesday night.

In general, it takes about two weeks for someone who has been infected to begin to feel ill, and often another week before that person is tested and the results are reported, said Eric R. Houpt, head of the Division of Infections Diseases and International Health at the University of Virginia Health System.

“When we see an increase in cases day by day … it isn’t telling us what’s happening currently,” Houpt said. “It’s really telling us what happened a few weeks ago.”

As more people begin to experience symptoms, the number of reported infections will continue to grow “several-fold,” he said.

“We’re not even talking about all of the asymptomatic or pre-symptomatic infections that are out there,” Houpt said. “No one has a great handle on how many of those individuals there are or how important they are for transmission. But I’m sure there are a lot of them.”

State and local health officials, along with commercial labs and several research facilities, have been ramping up their testing. In Virginia, 5,370 people had been tested as of Wednesday afternoon, according to the state health department’s website. The District had reported test results for 1,857 people as of Wednesday night.

Maryland has not tracked the total of number of tests conducted in the state, officials said. Fran Phillips, Maryland’s deputy secretary of public health, said the state is “working to get our arms around” that figure. Some hospitals and commercial labs have not been reporting their results to the state, she said.

“While they must all report to us immediately on a positive case — and they do — what we want to know now is exactly how many tests they are doing that are negative, so we can get a sense of the volume and also the positivity rate for our state,” Phillips said.

Virginia reported three other deaths Wednesday, as well: an adult from the Danville-Pittsylvania area, along the state’s southern border; and two women — one in her 80s and one in her 60s — from Virginia’s Peninsula in the eastern part of the state.

The Canterbury facility had 14 residents and four health-care workers who tested positive, including the three residents who died. That makes it the largest known outbreak at a health-care facility in the greater Washington region.

Early Thursday, D.C. Jail officials said a 20-year-old male inmate who had been housed in its Correctional Treatment Facility tested positive for the virus. The inmate is now in the infirmary, Keena Blackmon, a spokeswoman for the D.C. Department of Corrections, said in a statement. He is the first inmate to test positive at the jail.

D.C. officials said Wednesday that they plan to launch a drive-through testing site on the campus of United Medical Center, the city’s only public hospital, by late next week.

Children’s National Hospital is also offering drive-through testing, but only for children who have a doctor’s note saying they need the test and meet other criteria.

D.C. Health Department Director LaQuandra Nesbitt said the United Medical Center site will be able to test up to 300 patients a day.

People must fall into one of several prioritized groups to get tested, Nesbitt said: hospital patients, health-care-facility workers, patients in long-term-care facilities, patients over 65 and police, fire or emergency medical services personnel. They also must exhibit covid-19 symptoms. Health-care workers and first responders will be eligible for testing even if they exhibit only mild symptoms, Nesbitt said.

Amid the dire figures for rising infections, some good news emerged Wednesday.

Maryland officials said 17 people in the state have fully recovered. In the District, 21 people so far have recovered, while the number of D.C. firefighters under quarantine has gone down to 118, from 141 last week. Ten firefighters, including an assistant chief, have tested positive, officials said.

Virginia health officials said they are not tracking the number of full recoveries.

Washington National Cathedral found 5,000 respirator masks in storage that were purchased in 2006 and delivered them to MedStar Georgetown University Hospital and Children’s National Hospital.

But the spread of the virus remains unpredictable, officials warned.

Maryland officials noted that the majority of cases in the state are of people ages 18 to 64, with five under age 18. The youngest person infected in the state is a 10-month-old boy.

Phillips, the state health official, said none of the five children who are infected in the state have been hospitalized.

“But that makes the point of how very important it is for people to stay home,” she said. “Children can absolutely have this disease and can be spreaders.”

Northam made the same point in a stern message Wednesday to Liberty University President Jerry Falwell Jr. about that school allowing students to return to campus after spring break ended last week. Falwell had said 1,000 to 2,000 students were back on campus. In keeping with state bans on large gatherings, he said, most classes would be taught online.

In his message to Falwell, the governor cited a Bible passage from First Corinthians: “It is required that those who have been given a trust must prove faithful.”

“Proving faithful means providing clear and consistent guidance,” Northam said. “And it means respecting the duty that Liberty University has to its students, its staff, the Lynchburg community in which it is located and our commonwealth.”

Fenit Nirappil, Rebecca Tan, Michelle Boorstein, Keith L. Alexander and Laura Vozzella contributed to this report.