The massive Sturgis Motorcycle Rally, which brought more than 460,000 people to a tiny city of 7,000 residents in South Dakota in August, was a “superspreader” event that was responsible for more than 260,000 new cases of COVID-19 across the nation.
That’s the provocative conclusion from a new study from the Center for Health Economics & Policy Studies at San Diego State University, which also estimated that these cases cost the nation around $12.2 billion.
These numbers have been rejected by city and state officials, who noted that the study has not yet been peer reviewed. If more than a quarter of a million people really had been infected as a result of the rally, stories describing these cases would be showing up in newspapers across the country, Sturgis City Manager Daniel Ainslie told BuzzFeed News.
“It’s irresponsible to do this kind of hit piece on a small community,” he said of the new study.
But if the numbers stand up to subsequent analysis, it would make the Sturgis rally, held from August 7 to 16, the biggest single “superspreader” event in the US coronavirus epidemic. “This event is accounting for 19% of the national cases over this time period,” Andrew Friedson, a health economist at the University of Colorado, Denver, and one of the researchers behind the study, told BuzzFeed News. “That’s huge”
The researchers looked at county-level data on new confirmed COVID-19 cases, as well as anonymized cellphone tracking data released by the company SafeGraph. This included the recorded home location for each phone, allowing the researchers to determine how many attendees came from each county across the nation.
They then compared the trajectory of cases in counties with many Sturgis attendees, such as Clark County, Nevada, and Maricopa County, Arizona, to those with previously similar case trajectories that had few residents who traveled to Sturgis. This allowed the researchers to estimate the number of new cases resulting from exposure to the coronavirus during the rally — including cases caused by secondary transmission after attendees returned home. Extrapolating to rallygoers nationwide gives the figure of more than 260,000 new coronavirus cases caused by the Sturgis gathering.
“This is a very compelling assessment of the Sturgis motorcycle rally that seeks to quantify the impact — the findings are startling,” Saskia Popescu, an epidemiologist at the University of Arizona in Phoenix, and a member of the Federation of American Scientists’ Coronavirus Task Force, told BuzzFeed News by email.
Noah Haber, an expert in research methodology at Stanford University, told BuzzFeed News he could see no obvious problems with the study, but warned that “the devil is in the details.” The statistical methods involved are “quite tricky,” said Haber, who anticipated that other researchers will be picking through the data themselves to see whether they agree that the Sturgis rally was as massive a superspreader event as Friedson and his colleagues claim. “This is one of those things where you have to spend a lot of time,” Haber said.
The study comes from the same researchers who in June concluded that the Black Lives Matter protests that erupted across the nation from late May did not cause spikes in coronavirus transmission.
In July, the same team also studied President Donald Trump’s June 20 rally in Tulsa, Oklahoma, attended by around 6,000 people. Although the head of the local health department had suggested that the rally “more than likely” had contributed to a subsequent surge in COVID-19 in Tulsa County, Friedson and his colleagues again found no evidence that the gathering significantly changed local patterns of coronavirus transmission.
Friedson told BuzzFeed News that the BLM protests and the Trump rally took place in large cities where the people who attended were outnumbered by the total number of residents in the city. What’s more, cellphone tracking data indicated that city residents were more likely to stay at home during the protests and the Trump rally. “People were worried there was going to be violence at these events,” Friedson said.
This means that any increase in viral transmission at the protests or the Tulsa rally was likely offset by a reduction in spread in the wider city population.
Sturgis was very different. Not only were the 7,000 residents of Sturgis vastly outnumbered by the rallygoers, but the cellphone data indicated that they were less likely to stay at home during the event, Freidson said.
Epidemiologists had been worried about the Sturgis rally, given the huge numbers of people involved and opposition to mask-wearing and social distancing among many attendees. At a concert in Sturgis widely criticized by public health experts, Smash Mouth singer Steve Harwell told the crowd: “Now we’re all here together tonight. And we’re being human once again. Fuck that COVID shit.”
“Large gatherings where mask use and physical distancing is observed to be limited (especially when these interventions are left to the discretion of attendees) certainly have the potential to result in super-spreading events,” epidemiologist Maia Majumder of Harvard University told BuzzFeed News by email. “Furthermore, when folks are traveling from far and wide to attend said gatherings, there are multiple opportunities to seed case clusters.”
As well as seeding cases across the nation, Friedson and his colleagues found that it caused a surge in cases in the state of South Dakota. Although the number of new cases per day had been rising in South Dakota before the rally, it took off rapidly in the weeks that followed.
The new study estimates that the rally increased the case rate in South Dakota by between 3.6 and 3.9 per 1,000 people — or a total of more than 3,000 cases across the state as a whole.
In a press briefing earlier today, the South Dakota Department of Health cast doubt on these numbers, noting that just 124 state residents who tested positive for COVID-19 had reported attending the rally. “The results do not align with what we know of the impacts of the rally among attendees in the state of South Dakota,” state epidemiologist Joshua Clayton said when asked about the new study.
Friedson said that self-reports like those used by the state's health department are unreliable because people may not report accurately. Such reports also don't account for other people attendees may have infected. “You cannot rely on these types of reports to tell you the number of cases,” he told BuzzFeed News.
The researchers’ estimate of $12.2 billion in costs from the cases triggered by the Sturgis rally comes by extrapolation from a study published last month, which estimated that each case of COVID-19 incurs total economic costs of about $46,000.
While those costs would be spread across the nation, the economic benefits of the Sturgis rally were mostly felt locally. But Ainslie, the Sturgis city manager, rejected criticisms that the city should have canceled the event.
“What people continue to miss is that the vast majority of people would come to the event irrespective or not of whether the city was hosting it,” said Ainslie, who added that the city did not have the legal authority to impose a mandate to wear masks during the rally.
“We couldn’t do that,” Ainslie told BuzzFeed News. “We had plenty of masks available and we provided them.”