Val Arkoosh knew it was coming, a moment that would propel her team’s weeks of preparations for the new coronavirus into high gear.

For Arkoosh, chair of the Montgomery County Commissioners, everything changed last weekend, when the county’s first suspected infections were reported. Health officials soon learned that a resident who tested positive had come into contact with numerous other people.

Right away, Arkoosh said, “we knew that the possibility of a more rapid spread in our community had increased. So we just needed to make sure that we were prepared for that, with a little less lead time than we maybe would have liked."

County officials canceled meetings and warned against holding large gatherings. Schools closed and jury trials stopped. By the end of the week, much of the county was on lockdown, following an order by Gov. Tom Wolf to close nonessential businesses in an attempt to mitigate the spread.

Montgomery County found itself the epicenter of the COVID-19 outbreak in Pennsylvania, its 20 presumptive positive cases the most reported in the state. And Arkoosh, with decades of experience working as a physician and in public health, is uniquely positioned to lead the fight.

At news briefings held each afternoon, Arkoosh has released more information about infected patients than have nearby counties. Montco has provided maps of the municipalities where they live. She has offered glimpses into the county’s ever-evolving plans for such contingencies as sharing law enforcement services to making sure schoolchildren and seniors have access to food.

“I am a parent, and a physician, and a public official," Arkoosh said this week, “And I bring all of that to bear as I approach this situation.”

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During an interview Friday morning at the Montgomery County Emergency Operations Center, Arkoosh declined to specify which patient led the county to ramp up its response to the new coronavirus. But officials have said that a cardiologist at Children’s Hospital of Philadelphia’s campus in King of Prussia tested positive Monday and that he had contact with about two dozen patients before he was hospitalized in critical condition.

Contact tracing, to establish where a 70-year-old Cheltenham woman contracted the virus, has proved unsuccessful, which provides Arkoosh with another indicator that it was spreading within the community.

And the determination that a patient had contact with numerous other individuals, “alerted us to the possibility that a purely containment strategy might not be successful.”

Arkoosh is 59, an Omaha, Neb.-reared Springfield Township resident who once headed the anesthesiology department at Drexel University’s medical school. She then earned a master’s degree in public health from Johns Hopkins University. Before she ever held office, she was politically active; in 2007 she advocated for health-care reform in Washington as part of the National Physicians Alliance.

She served as chair of the Montgomery County Board of Health and in 2012 was part of Josh Shapiro’s transition team when Democrats assumed county leadership. Shapiro, now state attorney general, said he took notice of both her strong background in health and what he saw as her political savvy.

After an unsuccessful run for Congress in 2014, Arkoosh was appointed to the board of commissioners the next January to fill a vacancy. After winning election that November, she took over as chair when Shapiro stepped down a year later.

Much of her work went on behind the scenes, Shapiro said. But she was willing to step into public view to champion a cause, such as the day in October 2015 when she staged an awareness campaign by injecting Shapiro and then-Commissioner Bruce L. Castor Jr. with flu vaccines at a public meeting.

“It was a jovial moment,” Shapiro said. “And there were a lot of people who’d stop me after that, and they’d laugh. But a lot of people also told me that it reminded them to get their flu shot.”

And under her leadership, he said, the county expanded the number of places that people could get the vaccines.

Castor said Arkoosh has overseen numerous other outbreaks of infectious disease in the county: West Nile virus in 2018, Zika in 2016, and regular bouts of other illnesses like the flu.

“When it comes to dealing with something on this scale,” he said, “she certainly would be prepared in a boatload of ways.”

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County leaders were planning for the coronavirus when it surfaced in China. In late February Arkoosh convened a meeting of several dozen officials to discuss preparing the county’s 2,700 employees.

Officials met to review the operations plan with an eye toward virus containment and created a communication plan with local school districts, businesses, and health-care providers, said Michel Masters, a program supervisor.

Health officials started monitoring individuals who are at a higher risk for contracting the virus and planned regular check-ins to discuss quarantine plans.

In the days before the first positive cases emerged in Montgomery County, representatives from the county Department of Public Health and Department of Public Safety offered a detailed presentation at the regular commissioners’ meeting, giving virus preparedness precedent over other regular business.

After the first cases were confirmed, Arkoosh began offering guidance on how to decide whether to attend events or parties. She has repeatedly asked business owners to consider providing paid sick time, even temporarily.

A week ago she stopped shaking hands and urged others to do the same. She suggested that people take advantage of the nice weather and go outside for walks or bike rides to get fresh air.

“I wanted to be transparent out the gate,” she said. “Everyone is aware this is a pandemic. This is no time to be cute. I want people to believe they can trust me to give them as much information as I can and know that it’s going to be accurate."

Arkoosh said her experience working in Level 1 trauma centers had prepared her to handle a variety of emergencies. She also gained the confidence to make difficult decisions. She knows residents will be inconvenienced by the school closings, for example, but believes delaying that step would have made it much harder to stop the spread of the virus.

“If Governor Wolf hadn’t been prepared to close the schools, I would have closed the schools,” she said. "And I can almost guarantee you that if these mitigating measures work, people are going to look back and say, ‘What did they do all that for?’ "

Reporters Vinny Vella and Justine McDaniel contributed to this article.