The Sturgis Motorcycle Rally led to significant spread of the novel coronavirus in the event’s home state of South Dakota and in other parts of the United States, a team of researchers said in a newly released study that is disputed by state officials.

The report from San Diego State University’s Center for Health Economics & Policy Studies used anonymized cellphone location data and virus case counts to analyze the impact of the 460,000-person event that took place last month, believed to be one of the largest events held during the pandemic. Health officials had expressed concerns about the rally, which, the researchers noted, “represents a situation where many of the ‘worst case scenarios’ for superspreading occurred simultaneously.” Those included the event being held over 10 days, attracting a significant out-of-town population and involving attendees clustered together, with few wearing masks.

The consequences were “substantial,” the researchers concluded. By analyzing the parts of the country that had the highest number of Sturgis attendees and changes in coronavirus trends after its conclusion, they estimated 266,796 cases could be linked to the rally. That’s about 19% of the number reported nationally between Aug. 2 and Sept. 2, and significantly higher than the number state health officials have linked through contact tracing. Based on a COVID-19 case statistically costing about $46,000, the researchers said, that would mean the rally carried a public health price tag of $12.2 billion.

“This is enough to have paid each of the estimated 462,182 rally attendees $26,553.64 not to attend,” the paper said.

Officials in Sturgis, a 7,000-person city in the Black Hills, considered postponing the 80th edition of the rally. But the event encompasses hundreds of miles outside their jurisdiction, on state-licensed campgrounds and roads traveled by bikers. After determining that many would come regardless of what the city did, city councilors voted to allow the rally so they could prepare for their arrival. The South Dakota Department of Transportation put the event’s attendance at 462,182, down 7.5% from the previous year.

On Tuesday, state health officials acknowledged that mass gatherings carry a higher risk of spreading the novel coronavirus but questioned the San Diego State University analysis and its methodology.

During a phone conference with reporters, state epidemiologist Josh Clayton and Secretary of Health Kim Malsam-Rysdon noted that the paper has not been peer-reviewed. They said the researchers did not account for a trend of already-increasing case counts in South Dakota or the possibility that school reopenings contributed to the rise. They also questioned the use of cellphone data, with Malsam-Rysdon saying the study “makes assumptions around people’s cellphone use and tries to apply that to case counts.”

“What I have to say at this point is the results do not align with what we know for the impacts of the rally among attendees in the state of South Dakota,” Clayton said.

Gov. Kristi Noem, a Republican who welcomed the motorcycle rally and has eschewed mask mandates and stay-home orders imposed in other states, called the study “grossly misleading” and said it “isn’t science; it’s fiction,” the Rapid City Journal reported.

The South Dakota Department of Health has reported 124 cases linked to the Sturgis rally through contact tracing. A Washington Post survey of health departments found an additional 204 rally-linked cases in 20 states. One death has been reported – that of a Minnesota man in his 60s, who had underlying conditions and was hospitalized with the virus after returning from Sturgis.

Public health experts have cautioned that such tallies will likely be an undercount because of the sheer number of attendees, the many health departments involved and the difficulty of contact tracing. As a result, determining the true impact of the event is a near-impossible task. But Derek Chapman, the associate director for research at Virginia Commonwealth University’s Center on Society and Health, told The Washington Post that he was not surprised by the 460,000-plus attendance figure.

“It only takes a small number of people from places that have high infection rates to have a high likelihood that some of them are carrying the infection,” he said. “It’s kind of more of a mathematical certainty that you’re going to have possible asymptomatic cases in that event space and that it will spread over that 10-day period and that those people will head back to their own communities and continue spreading.”

The San Diego State University researchers noted that although restrictions on large-scale gatherings are “ubiquitous,” there has been “little empirical evidence on the contagion dangers.” They previously analyzed the effects of protests and President Donald Trump’s Tulsa, Okla., rally this year. Neither caused significant increased spread of the virus, they concluded, possibly because those events were offset by increases in other residents staying home.

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