Nine percent of COVID-19 diagnostic tests are coming up positive in Minnesota, a warning sign to state health officials that the infectious disease is spreading rapidly.

The increase in the seven-day average positivity rate came on Tuesday as the Minnesota Department of Health reported a single-day record of 3,483 new infections and 15 deaths from the novel corona­virus that causes COVID-19. Totals in the pandemic have reached 157,096 infections and 2,499 deaths.

Infections were reported Tuesday from 86 of 87 Minnesota counties, reflecting the viral spread that health officials said is happening in gatherings, large and small, across the state.

The positivity rate had hovered for weeks around 5%. But nine mostly rural and western counties had seven-day average positivity rates above 10% in the week ending Oct. 17, and Red Lake County's rate was above 15%.

"It's just not one or two big notable events that's causing this incredibly high level of community spread," state Health Commissioner Jan Malcolm said. "It's the happy hour at the end of the long week with just a couple friends or brunch on the weekend with maybe a few cousins. ... It's the weddings. Everybody really tries hard during the ceremony to comply with the safety guidance and much of the reception, but as the night wears on, people start letting their guards down."

Workplace outbreaks among employees increased 76% to 95 in the week ending Oct. 24. The state has investigated 172 bar or restaurant outbreaks and identified 92 that likely generated seven or more infections. Eighty-two weddings have been linked to 756 infections.

Health officials urged people to avoid large gatherings, wear masks in indoor public places, maintain social distancing and stay home when sick to reduce the spread of the virus. They also asked that people cooperate when contact tracers call to identify any viral exposures or their sources.

State infectious disease director Kris Ehresmann estimated that more than a third of people are reluctant to share details, because they worry about informing on parties, bars or events where the virus could have spread. Ehresmann said people might be trying to protect their communities and keep their schools open but are having the opposite effect.

"This makes it harder for us to get to potential high-risk contacts who may go on to get COVID and pass it along to others," she said. "This just accelerates the spread we are seeing even more."

The positivity rate is a key indicator of the pandemic because it reflects broadening spread of the virus, regardless of the amount of testing. It is one of five measures on Minnesota's "dial back" dashboard to assess the adequacy of the state's response to the pandemic. If the rate climbs above 15%, Minnesota would be falling short on four of those measures.

Gov. Tim Walz earlier this fall had said he would consider scaling back restrictions under his emergency orders if the positivity rate dropped below 4% and the rate of transmission from unknown community sources dropped below 20%. Minnesota briefly reached 4% in mid-September before the positivity rate surged amid the reopening of K-12 schools and colleges and a broader spread of the virus.

On Tuesday, Walz said in a statement that the virus continues to be "merciless" and that Minnesotans need to heed the advice of health officials on how to prevent its spread and take advantage of testing options.

"I've said from the beginning, the virus' spread will dictate our course and we are well into a dark chapter in the story of this pandemic," he said.

In a report distributed Tuesday, the White House Coronavirus Task Force designated 38 Minnesota counties as "red zones" due to high case rates and suggested additional mitigation strategies because "less intense mitigation levels are unlikely to succeed."

The last time the state's positivity rate was at 9% was late May, when the state was reporting fewer than 10,000 tests per day and reserving them for people with symptoms, or people in long-term care facilities or high-risk workplaces.

The state by comparison has reported at least 20,000 tests in five of the past six days, including results from seven free state saliva testing sites that are available to people regardless of their symptoms or viral exposure risks.

Minnesota's infection rate for the past two weeks is 462 per day per million people, according to the COVID Exit Strategy website, compared to rates of more than 1,300 in the Dakotas, 587 in Iowa and 810 in Wisconsin.

Infection growth in the state appears most rapid right now in southwestern Minnesota, Ehresmann said. "Southwestern Minnesota doesn't have a particular workplace or school or jail or long-term care facility outbreak. It's simply experiencing spread from events in neighboring states and the community."

Most COVID-19 cases involve mild or no symptoms. Of the total known cases, 134,227 people have recovered to the point they are no longer considered infectious or required to isolate themselves.

Health officials are concerned about the rising volume of infections requiring hospital care, though. Minnesota hospitals on Tuesday reported a record 852 people with COVID-19 admitted to their beds, including 197 people who needed intensive care due to breathing problems or other complications from their infections.