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Minnesota’s rate of community spread of COVID-19 is skyrocketing. Here’s why health officials aren’t concerned

Community spread refers to cases of COVID-19 where contact tracers can’t determine the source of infection. A high rate of community spread was thought to indicate a pandemic out of control.

In recent months, the number of new cases in Minnesota has leveled off, dropping from a high of 125 new cases per 100,000 residents in mid-November to 13.2 new cases per day in the most recent data.
In recent months, the number of new cases in Minnesota has leveled off, dropping from a high of 125 new cases per 100,000 residents in mid-November to 13.2 new cases per day in the most recent data.
REUTERS/Callaghan O'Hare

Over the last two months, most COVID-19 indicators have showed the virus on the decline in Minnesota.

“I don’t like to get too far over my skis, but I think it is time to know — we’re winning this battle,” Gov. Tim Walz told municipal leaders mid-February. “This thing’s coming to an end. We’re now down to 4 percent positivity rates.”

That’s not all: Intensive care hospitalizations have dropped to levels not seen since the virus first landed in Minnesota, and in recent months, the number of new cases has leveled off, dropping from a high of 125 new cases per 100,000 residents in mid-November to 13.2 new cases per day per 100,000 residents in the most recent data.

There is one indicator that has gone in the opposite direction, however: community spread. That’s the share of cases where health officials don’t know the source of exposure, meaning the virus case couldn’t be tied to a specific event, locale, family member or friend. Seeing too many of these cases is concerning because they point to a pandemic that is not being contained effectively by contact tracing.

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Since July, the share of “community spread – no known exposure” cases, as these cases are called, has hovered near or above the 30 percent threshold that represents a high level of concern for public health. But since mid-January, even as case numbers slowed and Minnesotans began to be vaccinated for COVID-19, the share of cases with no known exposure has taken a steep turn upward, well into levels that the state considers “high risk” on its COVID dial-back dashboard.

line chart showing a big rise in covid-19 cases with no known exposure in the first months of 2021
Taken on its own, such a precipitous climb in the share of unknown exposure cases would sound alarm bells for public health officials. But neither state nor local public health officials seem concerned.

Kris Ehresmann, the Minnesota Department of Health’s Director of Infectious Disease said the increasing level of unknown exposures may be more a reflection of people’s wariness of the pandemic than unmitigated spread.

People may be more wary to tell contact tracers where they’ve been for fear of the consequences for others, she said. For example, they might be reluctant to talk about their sports team practices because of what that might mean for teammates or the gym they’ve been working out at lest it be forced to close.

Ehresmann said that after a year of the COVID-19 pandemic, she’s empathetic to the fact that some people have become despondent. But, she said, not being forthcoming about your activities limits public health’s ability to respond, too.

Meaghan Sherden the lead epidemiologist in Olmsted County said that since mid-January, the share of cases in her county with no known exposure has risen to nearly 40 percent, an increase similar to the state’s. But a close examination of the numbers tells Sherden that this increase is actually masking good news.

As people living and working in congregate care, such as nursing homes, assisted living and group homes and health care workers have been vaccinated, the number of cases contact tracers have traced to those settings has trended down.

“We have seen our congregate care trend down to barely maybe 1 percent of our exposures over the last few weeks,” Sherden said, compared to that share being as high as 20 percent at the height of the winter wave and around 10 percent to 15 percent right before long-term care was vaccinated around the end of December.

So while the share of unknown exposures is up, the number of them is not: they’ve just grown as a piece of the overall exposure pie as cases likely to be known exposures in congregate care and health care have dissipated.

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Weekly data on exposures from the state tell a similar story, with declines in both the number and share of exposures in congregate care or health care, leaving community-unknown exposures, though down, a more sizable chunk of cases.

New cases by week and exposure type
Source: Minnesota Department of Health weekly reports

While this is good news, Sherden emphasized that the pandemic still isn’t over. Some public health experts are warning that a spring wave is still possible, and people need to remain cautious as vaccination efforts continue.

“All of us are really really happy to see it, but always trying to be that cautious optimism,” she said.