Health care workers took the temperature of every visitor of Essentia Health who crossed over a skywalk bridge from the adjoining parking deck in April. (The Minnesota Star Tribune)

DULUTH – When the National Guard set up a free COVID-19 testing site in Duluth over Memorial Day weekend, more than 1,400 people came through.

Just one tested positive.

There has been one new confirmed COVID-19 case in St. Louis County since May 29, the longest plateau since the coronavirus was first detected in the area March 21.

While that is reason to celebrate, public health officials say residents — and visitors — must remain vigilant to continue keeping the pandemic in check.

"A lot of situations could change those numbers pretty quickly," say Amy Westbrook, the county's health director. "We haven't slowed down our planning because we anticipate we will still be seeing a peak at some point."

Westbrook said about 40% of the county's 119 cases have come from congregate living settings such as nursing homes. All 14 deaths attributable to COVID-19 in St. Louis County have occurred in long-term-care facilities.

St. Louis County is the state's sixth-most populous county, with about 200,000 people.

That smaller Minnesota counties have seen larger, deadlier outbreaks speaks to how the virus can easily spread in high-density workplaces such as meatpacking plants, which northeastern Minnesota does not have. Westbrook applauded the area's efforts to keep workers at home when possible, keep a safe distance when out and wear masks.

Hospital officials say strict limits on in-person visits and elective procedures also kept the virus from spreading faster.

"We've eliminated over 600,000 contacts," said Dr. Sarah Manney, Essentia Health's chief medical information officer.

As businesses reopen and life slowly resumes its normal patterns, there is a risk the virus spreads due to a lack of caution.

"As a population, at least 95% of us are still susceptible," said Dr. Andrew Thompson, an infectious disease specialist at St. Luke's in Duluth. "Cases are down and everyone wants to go out. We're still planning for a surge."

Until there is a vaccine or natural "herd immunity," officials said social distancing guidelines need to be followed.

Essentia is preparing to expand testing in long-term care facilities, day cares and schools that "will make a huge difference as we continue to flatten the curve," Manney said.

"We are still planning for a surge, because we don't want to be surprised," she said.

Statewide, a peak in cases is expected in late June or July, Westbrook said.

"What I am anticipating here is we're going to continue having little fires pop up in nursing homes or congregate settings such as shelters or a jail," Thompson said. "That is really where we have seen big numbers come in quickly."

Across the border, Wisconsin's Douglas County had reported 19 cases and no deaths from COVID-19 as of Thursday. There have been seven new cases reported since May 14, when many residents in Superior and around Wisconsin packed into bars after the state Supreme Court threw out the governor's stay-home order. No new cases have been reported since May 24, though officials are still urging caution.

"There are no promises with this virus," Manney said. "We're in a tough spot."

Brooks Johnson • 218-491-6496