Updated: 4:30 p.m., May 15 | Posted: May 14

Multiple cases of COVID-19 in Rochester appear linked to a single house party in mid-April according to Olmsted County’s top public health official.

Through testing and contact tracing, health officials believe that a single person who was just starting to show symptoms at the party spread the virus to 11 others at the party. Those individuals spread the virus to five others in the community, said Graham Briggs, Olmsted County public health director.

“We’ve been tracking this and working on interrupting this transmission that originally started at one house party, and have been working very hard to stop this from transmitting further out from where it originally did,” he said.

There were between 30 and 50 people at the party, and county officials said they haven’t detected any additional cases associated with the party in three weeks.

The news comes as Gov. Tim Walz prepares to lift the state’s stay-at-home order and relax other social distancing guidelines. 

To date, Rochester has 417 cases of COVID-19 and nine deaths. 

While the 17 cases associated with this party are only a sliver of the total in the area, Briggs said the situation illustrates that the coronavirus is fast and efficient.

"One person can turn into a dozen cases extremely quickly in a situation like this involving a house party with close contact between people,” he said.

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. 

Briggs said county staff pour through spreadsheets, looking for patterns like shared last names or addresses to link cases.

But a breakthrough in this case came when a doctor told the county they'd seen a patient with coronavirus who mentioned being at a party. Contact tracers started asking other people who had positive results whether they'd been to a party, allowing them to link all the cases to this single event.

“This house party is an example of one of those outbreaks where we can identify a common source or a common place where all these people were associated with,” Briggs said. “Then we can pull back on that cluster and see the spread that’s gotten to the families and the households.”

Olmsted County is among several in Minnesota 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. 

Briggs said the incident, which happened while the state’s stay-at-home order was in effect, is a case study in how contact tracing can help stop the spread of the virus. 

“That allows us to identify if a certain population or a group of people is at risk so we can actually get in front of this and keep people from getting exposed at all,” he said. 

Briggs said he's not sure if people who threw the party knew about the order. He characterized it as a group of 20-somethings who made a mistake.

He said the people involved were willing to work with the health department, and that no deaths were associated with the cluster.

Around the country, epidemiologists are finding that multiple cases or 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.

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