DULUTH – When two employees called to say they’d contracted COVID-19, staff at Grandma’s Restaurant in Canal Park canceled reservations for the upcoming weekend, scrambled to call off food orders and hunkered down for two weeks of quarantine.

The Duluth eatery, a regular stop for many visitors, has been closed for almost a week because the restaurant doesn’t have enough staff to operate regularly after asking those who worked closely with their COVID-positive colleagues to follow public health guidelines.

Over the past week, St. Louis County added new COVID-19 cases faster than any other Minnesota county — a trend that worries Brian Daugherty, president of Grandma’s, as the restaurant prepares to reopen.

“We’re a phone call away from having to go through this exercise again,” he said. “That’s the thing that keeps us all very anxious all the time.”

Of the 475 cases in St. Louis County as of Wednesday, more than half were confirmed in July. About three-fourths of the cases came from Duluth, though the virus has been detected in all parts of the state’s geographically largest county.

“There’s a lot of things to really be concerned about,” said Amy Westbrook, the county’s public health director — notably, the proliferation of community transmission.

In the spring and early summer, nursing homes were hit hardest by the pandemic as the virus entered facilities and spread rapidly. Now nearly one-third of those infected in the county are between the ages of 20 and 29. Statewide, that age group represents a quarter of cases, and 20- to 29-year-olds comprise 13% of the total population, according to census figures.

About 40% of St. Louis County residents testing positive for COVID-19 said they’ve attended restaurants or bars during the period they were likely exposed to the virus, Westbrook said.

She added that she’s hopeful Minnesota’s mask mandate will dampen the community spread of the virus. Westbrook called the next few weeks “critical” as the county watches to see whether the number of daily new cases, recently hovering close to 20, drops.

On Wednesday the Fond du Lac Band of Lake Superior Chippewa reported its first two confirmed cases on the reservation, part of which is in St. Louis County, and a third case involving a band member tested in Duluth.

“We have been seeing an increase in cases with younger people throughout the state and country, and this is largely due to risky behavior, like gathering in large crowds,” said Samuel Moose, the band’s human services director. “We urge everyone to stay home and not engage in high-risk activities.”

Band Chairman Kevin DuPuis said “the virus knows no boundaries.”

“We are encouraging all Minnesotans to continue to take care of one another, stay home and take extra precautions as this virus enters our homeland,” he said.

Officials will also be keeping a close eye on hospitalization rates, which haven’t increased like reports of cases have. As of Wednesday, there were seven county residents in the hospital because of the virus and three in the ICU.

All 19 St. Louis County residents who have died from the virus were living in long-term care facilities and have ranged in age from 62 to 106 years old.

“I’m certainly worried it could become worse,” said Dr. Andrew Thompson, an infectious disease specialist at St. Luke’s in Duluth. “I don’t think we have any way to know where we are in this trend.”

There’s still at least a month left of peak tourism season for northeastern Minnesota, and fall colors draw large crowds to the North Shore through October.

“On July 4, the people from out of town came in and just basically demolished Canal Park,” said Dave Hoops, who noted that at least four restaurants or bars in Duluth’s popular tourist district have temporarily shut down in the past month after employees contracted COVID-19.

He closed Hoops Brewing last Friday after a worker texted that she tested positive for the virus. Hoops had already spent two weeks in mid-July quarantining after his college-age daughter lost her sense of taste and received a corresponding diagnosis.

“I’m not just blaming the tourists — people up here need to get serious,” Hoops said. “They were cavalier.”

Thompson, who said a lot of local cases have been tied to sports tournaments or family gatherings, said passing the blame to out-of-towners “might make it worse because then we ignore our own behavior.”

“I think we have to focus on the collective. We all have to focus on our behavior and do what we can to reduce risk,” he said, reiterating the importance of wearing a mask, washing hands and social distancing.

For as the leaves change and snow inevitably arrives, more locals will be closing their windows and spending time indoors. Thompson said some believe recent COVID-19 spikes in the south occurred as folks sought shelter from the blazing summer heat.

“It’s a recipe for a worsened transmission of a respiratory virus,” he said.

Staff writer Brooks Johnson contributed to this report.