SIOUX FALLS, S.D. — The Sturgis Motorcycle Rally in South Dakota spread COVID-19 to hundreds of thousands of people nationwide and its public health cost totaled billions of dollars, researchers said in a recently released paper, conclusions strongly disputed by South Dakota officials including Gov. Kristi Noem, who called the research "fiction."

The researchers from San Diego State University's Center for Health Economics & Policy Studies published a preliminary version of the paper late last week with the IZA — Institute for Labor Economics.

The paper, which has not been peer-reviewed, is based on anonymized cellphone location tracking data and is the first known research to estimate the COVID-19 case spread and public health cost of the 10-day rally in Sturgis, S.D.

The rally, which ended Aug. 16, is associated with both local and national surges in COVID-19 cases, the researchers found, and should be linked to about 267,000 cases with a all-in public health cost of $12.2 billion.

"If you want to evaluate large-gathering bans, this is how bad it can get," Andrew Friedson, associate professor of economics at the Colorado University Denver and co-author on the paper, said in a Tuesday, Sept. 8, phone interview with Forum News Service.

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The researchers, who have also evaluated large events held during the pandemic including President Trump's June rally in Tulsa, Okla., and Black Lives Matter protests which didn't appear to spread COVID-19 decided to evaluate Sturgis since it seemed like it could have been a major spreader of the virus.

"Sturgis just seemed like this perfect storm," Friedson said.

Rally linked to local, national surges

The cellphone tracking data showed about 10% of Sturgis attendees hailed from within South Dakota, with about 19% from border states and 72% from across the rest of the country, with heavy attendance from Arizona, California, Colorado, Iowa, Minnesota, Nebraska, Washington and Wyoming.

State transportation officials estimated about 460,000 vehicles attended the event, where many rally-goers notably went unmasked and didn't socially distance to reduce the spread of COVID-19 as they crowded together in bars, campgrounds and concert venues.

The Sturgis rally should be linked to 266,796 of COVID-19 cases reported nationwide between Aug. 2 and Sept. 2, the researchers said.

"Taken together, the results ... provide strong evidence that the Sturgis Rally appears to have been a super-spreader event for COVID-19," found Friedson and his fellow researchers. "We find significant case increases within the state of South Dakota as well as increases extending to counties from which relatively more residents attended the event."

Researchers found the rally was associated with COVID-19 case surges in Meade County, home to Sturgis, as well as South Dakota overall. There were also Sturgis-associated COVID-19 case surges in counties with a lot of Sturgis attendees, including counties in Colorado, Arizona, Nevada, Minnesota and Wisconsin.

The researchers' method matched South Dakota, Meade County and other counties to locations on similar COVID-19 case trends, then tracked what happened when the Sturgis attendees swarmed South Dakota and Sturgis and returned home.

Those states with COVID-19 infection mitigation strategies seemed to have limited the spread of Sturgis-related cases in their states, researchers said.

They estimate that the Sturgis-linked COVID-19 cases came at a public health cost of $12.2 billion, although that amount is a ballpark estimate because many of those who were infected and required treatment likely absorbed the costs themselves, the researchers found.

SD officials blast research, cast doubt on methods

South Dakota Gov. Noem blasted the research in a statement issued Tuesday afternoon.

“This report isn’t science; it’s fiction. Under the guise of academic research, this report is nothing short of an attack on those who exercised their personal freedom to attend Sturgis,” Noem said. “Predictably, some in the media breathlessly report on this non-peer reviewed model, built on incredibly faulty assumptions that do not reflect the actual facts and data here in South Dakota."

Noem provided no evidence to back up her claims. But on a regularly scheduled call with media on Tuesday, South Dakota health officials also cast doubt on the researchers' work.

It's only a preliminary paper, said Dr. Joshua Clayton, the state epidemiologist. He said the researchers didn't factor in an ongoing rise in COVID-19 cases or return to school of South Dakota university and K-12 students (a charge Friedson disputes, pointing to the method used).

"The results do not align with what we know of the impacts of the rally among attendees in the state of South Dakota," said Clayton, pointing to the 124 known South Dakota cases linked by contact tracers to the Sturgis rally.

When asked how to balance the researchers' estimate against the state's low reported number of cases linked to Sturgis, Kim Malsam-Rysdon, the secretary of the South Dakota Department of Health, encouraged reporters on the Tuesday media call to not take the researchers' work at face value.

"I would just caution you about putting too much stock into models, whether it be the potential impact of the Sturgis rally or other models that can't be verified by other factual numbers. I think that is the case with this particular white paper," she said. "I appreciate the dilemma, but we can't just make up numbers, either."

But Friedsen said the research was not a prediction, or future modeling, but instead used a statistical analysis comparing before-and-after COVID-19 case trends.

"These are not model projections. These are percent differences and actuals," Friedson said. "Yeah, I agree, I don't think you should be doing model-based projections either. This isn't a model-based projection. These are based on actuals. "

A Forum News Service analysis of publicly reported information has raised the tally of known COVID-19 cases linked to Sturgis to 317 in 13 states, but that number will be limited due to the patchwork nature of state case reporting and contact tracing, which isn't designed to report and track infections from an event with attendees from multiple states.

That per-state tally, per reporting by FNS, CNN and CBS, includes 124 in South Dakota, 51 in Minnesota, 30 each in North Dakota and Colorado, 23 in Wisconsin, 14 in Wyoming, 11 in Michigan, nine in New Hampshire, seven each in Nebraska, Montana and Washington; three in New Jersey and one in Idaho.

Minnesota state health officials last week announced the first-known COVID-19 death traced to the Sturgis rally: a 60-year-old Minnesota man with underlying symptoms.

Clayton said the Centers for Disease Control and Prevention is considering calling for states to submit data on all known COVID-19 cases linked to the event.