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A streak of rising coronavirus caseloads across the greater Washington region came to an end Tuesday after 20 consecutive days of increases.

For the first time since Nov. 3, the rolling seven-day average number of new daily infections in Maryland, Virginia and D.C. dropped, from 4,824 to 4,796 — a still-elevated number that is more than double the peak recorded in the spring.

The recent jump in caseloads prompted Maryland’s most populous jurisdiction Tuesday to toughen restrictions to slow the virus’s momentum.

Montgomery County officials reduced a cap on indoor gatherings from 25 to 10 people Tuesday and clarified a mandate requiring that masks be worn when interacting with others in public, unless eating or drinking. Wearing face shields alone or face coverings with a valve do not qualify, the order says.

The new restriction on gathering size is a response to recent contact tracing data that show the coronavirus is spreading at private events held among friends and family, officials said. It does not apply to dining establishments or other businesses, which can continue to operate at 25 percent capacity.

“We are entering a phase of covid-19 that is very worrisome, and we need every resident to understand what that means,” said Montgomery County health officer Travis Gayles. “The case counts are continuing to rise at an alarming rate, and we need to take more drastic steps to reduce transmission.”

D.C. and Prince George’s County have a 10-person cap on gatherings. In Virginia, 25 people are allowed in gatherings indoors or outdoors.

Ahead of the Thanksgiving holiday, Montgomery County Executive Marc Elrich (D) is also calling on Gov. Larry Hogan (R) to bring the state back to Phase 1 of its reopening.

“[The covid-19 spread] is only going to get worse and worse,” he said Monday evening. “And the things we loosened up contributed to this.”

New daily infections in the county have hit record levels in recent days, climbing to a seven-day average this week of 312 new daily infections.

Elrich said he does not intend to bring Montgomery back into Phase 1 unilaterally because of the large number of residents who regularly travel out of the county. He said he hopes Hogan will introduce more restrictions soon, but added, “I don’t believe that I can exert any meaningful pressure on him.”

Over the Thanksgiving holiday, Elrich said the county will focus on ramping up enforcement of existing regulations.

County officials broke up an outdoor party of more than 100 people this past weekend, Elrich said. Officials were alerted to the event, in the northern part of the county, when neighbors complained. Elrich said he doesn’t know whether the party’s hosts were fined.

“Look, we’ve told people, if we see things, we’re going to shut them down,” Elrich said. “We’re going to be out there.”

Maryland on Tuesday reported 1,667 new cases and 33 new deaths, Virginia added 2,544 new cases and 37 deaths, while D.C. had 119 new cases and one additional death.

While cases are surging, hospitalizations and deaths are lower than springtime highs. Almost 3,000 people are hospitalized in the region with coronavirus-related illnesses.

In D.C., Mayor Muriel E. Bowser (D) tightened restrictions Monday after similar moves earlier this month in Virginia and Maryland.

The new D.C. restrictions that take effect Wednesday prohibit indoor gatherings of more than 10 people and outdoor groups of more than 25 people. It also requires restaurants to close at midnight and to stop serving alcohol after 10 p.m. Capacity for indoor dining will drop from 50 percent to 25 percent beginning Dec. 14.

The fatigue of dealing with shutdowns was evident on Tuesday, when Anne Mahlum, founder and chief executive of fitness studio SolidCore, told Bowser in a letter her studios will remain open for workouts despite the restrictions.

Bowser’s order bans indoor exercise classes, although gyms can stay open.

“This is not an effort to defy you or be combative,” she wrote. The company said it has had 35,000 members in 346,561 classes around the country since June, “and not one instance of community spread,” Mahlum said in an interview Tuesday.

Mahlum praised Bowser’s leadership and said she shut down her studio in March, reopening in June with mask and distancing requirements for classes, and extensive cleaning protocols. The business is just breaking even, but it’s keeping people employed and fit, Mahlum said.

A Bowser spokeswoman said late Tuesday afternoon she had not seen the letter and didn’t immediately have a comment.

D.C. health officials said Tuesday the average coronavirus test in the city is taking more than three days to be processed, a number that has risen in recent days. That’s nowhere near as slow as July, when tests sometimes took more than six days to process, but it’s a worrisome sign for the city’s reopening metrics.

The three-day average means many who are waiting in long lines at public test sites are waiting significantly more than three days because the average includes hospitals and nursing homes, which get their results much more quickly.

The Washington region is seeing “an exponential increase” in new coronavirus cases, said John D. Voss, vice chairman for quality and safety at the University of Virginia Health System. He said the area has avoided caseload rates seen in other parts of the country, but battling the virus will depend on people’s behaviors through the Thanksgiving holiday.

“We’re not as bad as the Midwest,” Voss said, “but it could be we’re just behind them.”

He said many people are failing to follow the advice of public health officials, adding that the rate of infections won’t decline unless people alter their behavior.

He laid out a grim timetable: Holiday travel this week without appropriate precautions could lead to a rise in cases in seven to 10 days, with virus-related hospitalizations jumping in about two weeks. An increase in deaths from covid-19 could hit in four to six weeks, around late December.

Voss reminded the public that “it’s not too late to not travel” for Thanksgiving. He said travelers who think they are being “safe” by getting a test aren’t being as safe as they think, since it can take three to five days for symptoms to show.

People who decide to visit those outside their immediate household should wear a mask, stay six feet apart and eat outside, he said.

Julie Zauzmer and Fenit Nirappil contributed to this report.