EVERETT — A key data point that has become a barometer of Snohomish County’s success in fighting the new coronavirus is nearing levels seen in March, when the crisis was at its worst, the county’s top public health official said on Tuesday.

In the past two weeks, the county has seen about 97 COVID-19 cases per 100,000 residents, Dr. Chris Spitters of the Snohomish Health District said during a Tuesday media briefing.

The rolling two-week average fell from a high of nearly 131 in March and reached its low point at less than 20 in late May. But in the past six weeks, the marker has steadily risen in the county, heightening public health officials’ fears that the virus is making a comeback and could soon bring on a surge in hospitalizations.

“The fact is that we are not out of this crisis as the numbers bear out,” said Dr. Sandeep Sachdeva, chief medical officer of Swedish Edmonds and Swedish Mill Creek, during the briefing.

As health authorities continued to emphasize the importance of mask wearing and social distancing, Snohomish County joined a coalition of governments that announced public sector employees will continue to work from home until January 2021.

Everett and the city’s port, as well as King and Pierce counties, were also among the jurisdictions that extended teleworking.

“With COVID-19 case counts rising, teleworking remains one of the best tools we have to keep our staff safe — and also able to provide important services to our residents,” Everett Mayor Cassie Franklin said in a statement. “This virus doesn’t respect jurisdictional boundaries; working together as regional leaders is critical to slowing its spread in our communities.”

Snohomish County’s work-from-home policy was first instituted in mid-March, county Executive Dave Somers said at the news briefing.

“Some essential workers and folks that need to be on campus will be, but we’ll assess the circumstances as we go and make changes as necessary to keep everybody (as) safe and healthy as possible,” Somers said of the extension.

While new case numbers are trending upwards in many counties, others — such as King and Spokane — have seen plateaus or decreases, according to a report released Tuesday by the state Department of Health.

In Snohomish County, those who are getting sick are mostly young and less at risk of becoming severely ill with COVID-19, Spitters said. Of the county’s current cases, about 55% are people who are 15 to 39 years old, he said.

But Spitters and other local officials are concerned that COVID-19 cases could soon hit older populations hard, leading to more deaths and hospitalizations.

Statewide, the distribution of cases is beginning to weigh heavier on older adults. That trend is “now clearly mirrored in new hospitalizations, which are increasing across most age groups,” the Department of Health reported.

For the first time since March, deaths appear to be increasing in western Washington, according to the health department.

Swedish Edmonds, however, has seen a decline in the mortality rate of people hospitalized with COVID-19, Sachdeva said.

Overall, the hospital has admitted more than 200 people with the illness, and about 21% of them have died, Sachdeva said. In just the month of June, though, the mortality rate was 7%.

“I think we’ve gotten better over time,” Sachdeva said. “We have learned about this disease, how to manage this disease. We’ve literally been sort of building the plane and improving the plane as we fly it.”

About one-fifth of the some 200 COVID-19 patients admitted to the hospital were younger than 50. Despite their relatively young age, some of them — even those without underlying health conditions — became severely ill or died, Sachdeva said.

“While the preponderance of folks who get it are mildly ill, it’s still a Russian roulette who gets deadly ill,” Sachdeva said.

Meanwhile, demand for testing continues to increase, Spitters said. About 5,000 tests were done in the county last week, he said.

The health district is moving its drive-thru test site, which is currently at McCollum Park. Starting on Monday, the pop-up center will return to where it initially opened in March on Broadway near Everett Memorial Stadium.

The district aims to serve 500 people a day at the location, Spitters said.

Online registration for testing appointments will be available on the district’s website, snohd.org, later this week.

Spitters again encouraged residents to answer phone calls — even ones from unknown numbers — because someone from the health district could be trying to inform them that they were recently in contact with a COVID-19 case.

He cautioned the public to be wary of scammers, though. The health district’s contact tracers, who make such calls, will never ask for a Social Security number, bank account number or other personal or financial information, he said.

Rachel Riley: 425-339-3465; rriley@heraldnet.com. Twitter: @rachel_m_riley.