Small-town surges in COVID-19 are often fueled by large group gatherings and events, with a campground concert causing one southwestern Minnesota county to have one of the highest per capita infection rates in the state.

Lincoln County on the South Dakota border went from eight infections with the coronavirus that causes COVID-19 at the start of July to 53 infections at the end of the month. State contact tracing identified 28 infections as likely occurring at a July 4th concert at the Stoney Point Recreation and Campground in the county — with many of those cases involving local residents.

“We think this is under­reported,” said Kris Ehresmann, state infectious disease director, noting that one infected concertgoer knew of 20 cases in his friend group.

The outbreak is one of several that state leaders have identified since the June 10 limited reopening of indoor bars and restaurants along with campgrounds, fitness centers and entertainment destinations.

Individual event outbreaks are just a “stone in a lake,” Ehresmann said Friday, with the ripples being attendees who then spread the virus into their communities and to others who might be more at risk for severe COVID-19 cases or death. “As we see cases associated with a particular event and then those case beget additional cases, it’s that ripple effect that gets you to the point where you’re seeing cases in the community that don’t have a direct link,” she said. “And that’s what we’re concerned about.”

Minnesota is now reporting its highest rate in the pandemic of 35% of known COVID-19 transmissions involving unknown sources in the community. That means the virus is spreading beyond the ability of state health officials to track it.

While cases linked to bars in particular have involved younger adults — who are less prone to severe COVID-19 illnesses — health officials have found that they spread to higher-risk individuals. Some infected bargoers work in child care facilities and in long-term care or assisted-living facilities. So far, 76% of COVID-19 deaths have involved residents of such facilities due to their advanced age and underlying health problems.

In addition to health concerns, local communities now have the additional pressure of knowing that local school reopenings will be tied to COVID-19 case rates.

Gov. Tim Walz’s school reopening plan encourages full in-person classes for schools in counties with fewer than 10 infections per 10,000 people in the preceding two weeks. Restrictions gradually increase with higher rates until the state recommends all-remote learning for schools in counties with 50 or more cases per 10,000.

Lincoln, with a population of fewer than 6,000 people, has a case rate of more than 70. Neighboring Pipestone and Murray counties also have rates above the 50 per 10,000 threshold.

The ripple-effect concern is what prompted state health officials late Friday to disclose an infection involving an attendee at the North Star Stampede rodeo in Itasca County. The event was held in northern Minnesota last weekend with what health officials described as disregard for COVID-19 rules regarding social distancing and crowd sizes of 250 or less.

State Health Commissioner Jan Malcolm said the risk level for transmission at this event was elevated by the lack of people wearing masks, even though it was outdoors, and she asked attendees to be on the lookout for symptoms and to stay home if sick.

“People may have been infected with the virus, and we have an opportunity to prevent additional spread of the disease if we can get those in attendance to take the necessary precautions,” she said.

The infection involved a person in the 20s age range who suffered symptoms but didn’t need hospitalization.

Minnesota reported 779 coronavirus infections and six COVID-19 deaths on Friday, bringing the state’s pandemic totals to 1,600 deaths and 54,463 infections.

The state also reported that 312 Minnesotans with COVID-19 were admitted to hospitals and that 151 of them needed intensive care. That is the highest ICU number reported since June 27.

Regional highs and lows in COVID-19 activity have been part of the pandemic in Minnesota from the start.

Fairmont and surrounding Martin County had an early spike in cases this spring, but Lake of the Woods County in the far north didn’t have a case confirmed until last weekend.

Nobles County had an outsized 1,738 reported infections that were largely tied in early May to an outbreak in the JBS pork plant in Worthington. Its cumulative case rate is one of the highest in the nation, but its current two-week case rate is only 20.15.

That would permit schools in the county to consider a blend of in-class and online instruction for K-12 students this fall. Hennepin County has a similar case rate — though as the most populous county it has reported 17,317 cases in the pandemic.

At least some of the increase in infections since mid-June is being traced to large group activities, including two funerals and 12 private gatherings that included graduation parties, a group barbecue and a tubing party.

Case growth also is occurring in the northern resort region, with Beltrami County seeing case growth from 27 on July 1 to 184 now.

Not all spikes have been rural. The city of Edina showed an increase in teenager cases traced in part back to a party in June, but new cases have since declined.

Health officials said people can help manage case growth — and by extension help their schools reopen — by covering coughs, staying home when sick, wearing masks in public and maintaining a social distance of at least 6 feet from other unrelated individuals.

The state school reopening “plan alone won’t work if community spread accelerates,” Walz said.

Lincoln County saw its cases rise following the campground concert and then a community testing event in Tyler that found even more infections. The latest trends suggest that the identification and isolation of these cases might be paying off, though.

“Over the last couple of weeks, we’ve seen far fewer new cases,” said Carol Biren, a division director for Southwest Health and Human Services, a regional public health agency for multiple counties in southwest Minnesota. “Due to our smaller population, when we have one family of six test positive that can skew the data as well.”

Correction: Previous versions of this article misstated the Minnesota county that, along with Lincoln and Pipestone counties, has a COVID-19 case rate above the 50 infections per 10,000 people threshold. It is Murray County.