Sept. 9, 2020 -- The Sturgis Motorcycle Rally that drew 462,000 biker enthusiasts to South Dakota in August was a superspreading event, responsible for more than 260,000 cases of COVID-19 -- or 19% of the 1.4 million new COVID-19 cases from Aug. 2 to Sept. 2, claim researchers from San Diego State University and an independent research institute.
South Dakota officials strongly disagree. In a statement Tuesday, Gov. Kristi Noem called the report "fiction" and "grossly misleading." State Epidemiologist Joshua Clayton, PhD, said at a news briefing that the report numbers are ''a far cry" from reality. He said that 124 South Dakota residents who had attended the rally have been diagnosed with COVID.
A death from COVID-19 in Minnesota has also been linked to the rally.
Thomas Lee, PhD, an assistant professor of epidemiology at the University of Hawaii at Manoa, reviewed the study but was not involved in the research. "I do agree the event led to more cases," he says. "What's debatable is the actual number, and everyone is never going to agree."
About the Study
To arrive at the number of 260,000 COVID cases, the researchers used anonymous cellphone data to track movements from nonresidents, including their foot traffic at restaurants, bars, hotels, and campgrounds during the rally. They also found that local residents stayed at home less than usual during the rally, suggesting they were also attending or working at venues catering to the rally.
"We can see where people are coming from, what they are doing," says study co-author Joseph J. Sabia, PhD, a professor of economics and director of the Center for Health Economics and Policy Studies at San Diego State University. He is also a research fellow at the IZA Institute of Labor Economics.
They could also track which areas of the country sent the largest number of participants to the rally.
Next, the researchers used data from the CDC to look at where COVID cases were increasing. One month after the rally, COVID-19 cases increased by about six or seven per 1,000 people in Meade County, where Sturgis is located. Counties in the U.S. that sent the highest numbers of people to the rally had a 7% to 12.5% increase in cases, compared to counties that did not. Regions with stricter policies about bar openings and mask wearing also seemed to have fewer cases, Sabia and his team found.
Finally, the researchers used a previous estimate that each COVID-19 patient averages a $46,000 medical bill. They concluded that the rally generated public health costs of about $12.2 billion.
The research is not peer-reviewed.
"This is a discussion paper, or a working paper," Sabia says, noting it is a common practice in economics research.
While the researchers did find a correlation of COVID cases with the movement data, Lee says there is not enough information to see it as cause and effect, especially without contact tracing to back it up.
Sabia says the paper reflects another important point. "There has been a lot of discussion about the freedom to choose," he says. But ''the magnitude of the effects we are seeing [in the increase in cases] is not all from attendees. It's coming from community spread. Third parties who didn’t choose to go to this rally are now paying some of the price for a rally they did not attend."
Comparing Sturgis With Other Events
Not all large gatherings are superspreading events, Sabia says. In previous reports, Sabia and his colleagues researched the effects of President Trump's Tulsa, OK, indoor rally on June 20 and Black Lives Matter protests in 315 cities, and they did not find increases in COVID-19 cases related to either.
Why not? "One of the reasons is that local residents [in cities with Black Lives Matter protests] increased their stay-at-home time,'' Sabia says, probably due to fear of the virus or fear of violence.
For the Tulsa event, Sabia says, some restaurants and bars downtown closed voluntarily, and a smaller-than-expected crowd attended the event, probably helping to explain why that event did not lead to a spike in cases.