Olmsted County's top public health official said the rapid response of investigators was key to containing an outbreak of COVID-19 that was linked to a Rochester house party held in mid-April, after Gov. Walz issued his stay-at-home decree.

Officials say an unidentified individual who was "developing symptoms" attended the party and infected 11 other party-goers. They in turn exposed and infected five other people before public health officials were able to track down and contain the spread.

"I think it is an important story about COVID-19, about how investigation works and how quickly this virus moves through a population," said Graham Briggs, Olmsted County director of public health. "Luckily, we dodged any long-term consequences with this particular outbreak."

Though the party happened a month ago and was first mentioned by Rochester Mayor Kim Norton on social media soon afterward, the party-linked outbreak slid under the radar until Olmsted County Commissioner Mark Thein posted about it Thursday on Facebook.

Thein said he highlighted the outbreak on social media after hearing about the party and its viral consequences during a regular Thursday meeting with county officials. He said he wanted to drive home the message that even though some freedoms are being restored, people still need to be wary of COVID-19. Gov. Tim Walz's stay-at-home order expires Monday.

To spice up the post, Thein attached an image of a group of happy, smiling party-hardy young people. Some thought the photo was taken at the party, but it wasn't. Thein said he used a generic Google image to dramatize his message. It worked.

"I just figured, as we are opening up as a county and state, we're going to be tempted to do things that we used to do before this thing. And we ought be smarter than that until this pandemic is ended," Thein said. "Just because the governor says we can open up a little bit, it doesn't mean we can forget about social distancing and pretend like this never happened."

Heightened attention also focused on the party because of a misunderstanding that the party was responsible for more infections than actually happened.

The renewed scrutiny given to the party occurred after the Wisconsin Supreme Court struck down Gov. Tony Evers' stay-at-home order, leading to a flood of social media images of bar patrons at jam-packed taverns and watering holes.

Officials say the house party attracted between 30 and 50 young adults, mostly in their 20s. Briggs said investigators haven't seen any additional coronavirus transmission beyond the five on the outer ring of the ripple effect.

More than 40 clusters within Olmsted County have been identified since the pandemic started. The Rochester party was responsible for one of the bigger outbreaks, with 17 infected. Briggs mentioned one bigger, a work site-related outbreak that caused more than 20 to become sick. He did not identify the work site because of privacy issues.

Briggs credited "true detective work" by doctors, epidemiologists and public health officials in tracking down and limiting the spread of the virus ignited by the house party.

"Instead of looking under cushions and finding murder weapons, these epidemiologists are looking at spreadsheets and numbers and running analysis," Briggs said.

Briggs was uncertain whether the people at the party were aware that they were violating Walz's stay-at-home order. Asked by a reporter whether the partiers should be sanctioned or punished, Brigg said securing their cooperation was more important.

While the party was a mistake, he expressed appreciation for the cooperation that people at the party provided health officials in helping "interrupt transmission."

"In this situation, we were lucky the (people) were able to work with us. It did interrupt transmission," Briggs said.

In Olmsted, there have been a total of 417 infections with 18 new cases reported Friday. Of those, 186 are considered active and 231 are considered recovered. Nine people have died of the illness.

Briggs said that Olmsted County has been able to find the source of 85 percent of the area’s cases through contact tracing, a process in which health staffers interview patients who have tested positive for COVID-19 to find out who else they’ve been in contact with.

Olmsted County is among several counties in the state whose staff have been trained by the state health department to do the detective work of figuring out where cases start and how they spread.

State officials say that process, paired with more testing, are key tools in slowing the virus and in knowing when to safely reopen the economy. They’re asking for $300 million from federal coronavirus response funds to ramp up case investigation and contact tracing statewide.

Around the country, epidemiologists are finding that multiple cases of coronavirus can be linked to single events. For instance, in California, a birthday party held during the state’s shutdown led to multiple cases of COVID-19.