A new study by the IZA Institute of Labor Economics examining the Sturgis Motorcycle Rally in August links more than 250,000 new coronavirus cases nationwide to the annual event. The rally, which drew over 400,000 attendees to Sturgis, South Dakota last month, was widely criticized for its lack of safety and protocols and has, from the start, seemed like a prime subject for a case study on potential “super-spreader” events.

The four economists from San Diego State University’s Center For Health Economics and Policy Studies (CHEPS) who authored the report (Dhaval DaveAndrew I. FriedsonDrew McNichols, and Joseph J. Sabia) used anonymized cellphone data, local health records, and data from the CDC to conclude that an estimated 266,796 coronavirus cases could be connected to the rally—representing roughly 20% of the 1.4 million new coronavirus cases in the U.S. between August 2nd and September 2nd.

Based on the increase in case count, the paper estimates that cases connected to the rally resulted in more than $12 billion in public health costs, not including the cost of any deaths that may have stemmed from a case there.

The $12.2 billion cost is based on a separate estimation that $46,000 is spent per positive COVID-19 case. As the researchers note to put the hefty sum in perspective, “This is enough to have paid each of the estimated 462,182 rally attendees $26,553.64 not to attend.”

Though the researchers acknowledged that the actual public health cost of the rally’s impact was difficult to accurately pinpoint, “this calculation is nonetheless useful as it provides a ballpark estimate as to how large of an externality a single superspreading event can impose, and a sense of how valuable restrictions on mass gatherings can be in this context.”

As the as-yet not peer-reviewed study, titled “The Contagion Externality of a Superspreading Event: The Sturgis Motorcycle Rally and COVID-19,” notes, “This study is the first to explore the impact of this event on social distancing and the spread of COVID-19 … The Sturgis Motorcycle Rally represents a situation where many of the ‘worst-case scenarios’ for superspreading occurred simultaneously … the event was prolonged, included individuals packed closely together, involved a large out-of-town population (a population that was orders of magnitude larger than the local population), and had low compliance with recommended infection countermeasures such as the use of masks.”

In August, the Sturgis Motorcycle Rally made the news when videos of one of its nightly headlining music events, a Smash Mouth concert, showed thousands of attendees gathered in close quarters without masks. Meanwhile onstage, singer Steve Harwell could be heard saying, “F*ck that COVID sh*t!”

The study’s results come in contrast with officially-reported numbers from the event, which were compiled using direct contact tracing. As of September 3rd (per The Washington Post), just one death (a biker from Minnesota in his 60s) and 260 cases (across 11 states) had been reported.

South Dakota Governor Kristi Noem on Tuesday decried the study as “fiction.” As Noem said in a statement, “Under the guise of academic research, this report is nothing short of an attack on those who exercised their personal freedom to attend Sturgis. 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.”

“The results do not align with what we know for the impacts of the rally,” state epidemiologist Josh Clayton also said on Tuesday.

That discrepancy with the reported numbers is due to the fact that the state is identifying specific cases through contact tracing. This study takes a different approach, looking at the areas that sent the most people to the rally and how case trends changed after the event rather than direct contact tracing. While the official reported numbers (via contact tracing) and numbers derived from the model used for the study paint vastly different pictures, the disparity highlights the potential flaws of the model being used to track the spread of the virus in an official capacity.

South Dakota Secretary of Health Kim Malsam-Rysdon also disagreed with the methodology of the study Tuesday, noting, “I would just caution you about putting too much stock into models … that can’t be verified by other factual numbers. I think that is the case with that particular white paper.”

In a statement to Sioux Falls Argus Leader, Andrew Friedson, one of the authors of the study, noted, “We’re never going to be able to contact trace every single person from Sturgis,” Friedson said. “So if we want a good-faith estimate using, at the moment, the accepted statistical techniques … this is the best number we’re going to get in my opinion.”

Read the full IVA report regarding Sturgis and the spread of COVID-19, “The Contagion Externality of a Superspreading Event: The Sturgis Motorcycle Rally and COVID-19,” here.

[H/T Newsweek]