Testing for COVID-19 has risen in Minnesota in the last week, with 134,669 diagnostic tests being reported by state health authorities, and the number of cases of the infectious disease have increased right along with it.

The Minnesota Department of Health on Friday reported another 808 lab-confirmed COVID-19 cases in the state, bringing the total in the pandemic to 14,240. The state also reported another 20 deaths, bringing the toll to 683.

The state reported 498 COVID-19 cases in hospital care on Friday, including 200 needing intensive care.

COVID-19 is caused by a novel coronavirus, but as many as 80% of people with the infection suffer only mild symptoms. So far, 9,503 Minnesotans have recovered from their lab-confirmed cases, and are no longer required to isolate themselves to avoid spreading the virus.

The trouble with such a high rate of mild or asymptomatic cases is that it allows for rapid spread of the virus, which has now been confirmed in all but three counties in Minnesota.

"It really is a stealth virus," Dr. Ruth Lynfield, state epidemiologist, said in a media briefing on Thursday.

Modeling forecasts predicted an accelerated rate of infections as Minnesota begins to pull back on its social distancing restrictions, including Gov. Tim Walz's decision to allow a statewide stay-at-home order to expire on Monday.

Retailers will be allowed to reopen on Monday, and group gatherings of no more than 10 people will be permitted. Bars, restaurants and hair salons and other service businesses will remain closed until at least June 1, per the governor's new pandemic response strategy.

The Health Department anticipated having 460 contact investigators on staff by the end of this week to interview people infected and to identify others they may have exposed to the virus.

Investigators continue to use a federal threshold that people are at medium risk for infection if they spent 15 minutes within six feet of someone carrying the virus, said Kris Ehresmann, state infectious disease director. However, state interviewers are asked to use their judgment.

"If someone with COVID coughs in your face, then the 15 minutes doesn't matter," she said.

Investigators originally asked only about contacts of infected people after they experienced their first COVID-19 respiratory symptoms. Now, they ask about contacts 48 hours before the onset of symptoms, because of evidence that people are infectious before they know they are sick.

"As we continue to learn about COVID, our approach to case investigations is evolving," Ehresmann said.

COVID-19 continues to be harshest on the elderly and residents of long-term care facilities. Among all deaths, more than 98% involved people who were older or had underlying health conditions. Deaths reported on Thursday included someone in the 30s age range with such additional health problems. Residents of long-term care facilities made up 554 of all COVID-19 deaths so far.

Jeremy Olson • 612-673-7744

Twitter: @stribjo