'Worst-Case Scenario': Report Finds Sturgis Motorcycle Rally a Superspreader Event Infecting Over 260,000

Public health experts this week reiterated warnings against large gatherings following a new report that estimates the 10-day Sturgis Motorcycle Rally in South Dakota last month led to more than 260,000 Covid-19 cases around the country and cost an estimated $12.2 billion in public healthcare spending.

The research suggests that between August 2 and September 2, nearly one in five coronavirus cases was linked to the rally.

"The Sturgis Motorcycle Rally represents a situation where many of the 'worst-case scenarios' for superspreading occurred simultaneously," wrote the report's authors, including Andrew Friedson, an associate professor of economics at the University of Colorado Denver. "The event was prolonged, included individuals packed closely together, involved a large out-of-town population, and had low compliance with recommended infection countermeasures such as the use of masks."

Authors of the report, published by Germany-based IZA Institute of Labor Economics, tracked anonymous cell phone data from the rally and estimated the event helped spread Covid-19 to at least 263,708 people and cost billions:

If we conservatively assume that all of these cases were non-fatal, then these cases represent a cost of over $12.2 billion, based on the statistical cost of a Covid-19 case of $46,000 estimated by Kniesner and Sullivan (2020). This is enough to have paid each of the estimated 462,182 rally attendees $26,553.64 not to attend. This is by no means an accurate accounting of the true externality cost of the event, as it counts those who attended and were infected as part of the externality when their costs are likely internalized.

However, 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. Even if half of the new cases were attendees, the implied externality is still quite large. Finally, our descriptive evidence suggests that stricter mitigation policies in other locations may contribute to limiting externality exposure due to the behavior of non-compliant events and those who travel to them.

"This is a recurrent story of large crowds that disdain masks and distancing fueling superspreader events that keep driving the pandemic," Atul Gawande, surgeon and author, tweeted in response to the report.

In a Covid-19 media briefing Tuesday, Joshua Clayton, South Dakota's state epidemiologist, downplayed the institute's findings. He told reporters, "from what we know, the results [of the IZA report] do not align with what we know," and noted the study had not been peer reviewed.

South Dakota surged to post the nation's third highest per capita in Covid-19 cases this month, but, possibly due to the state's contact tracing protocols, South Dakota health experts have not attributed nearly as many coronavirus cases to the rally held August 7-16.

According to reporting by the Rapid City Journal on September 3:

118 South Dakotans have Covid-19 as a result of attending the Sturgis Motorcycle Rally, the [state Department of Health] reported Thursday.

Clayton said the state is basing its rally tally on South Dakota residents who in 14 days prior to their illness onset visited Sturgis or attended an event that would be considered part of the motorcycle rally prior to their illness.

Clayton said the state is not counting secondary infections in their tally. A secondary infection would be someone who went to the rally, contracted Covid-19, and then infected a friend or family member who was not at the rally.

National public health experts were quick to point to the consequences of mass gatherings in light of the new findings:

South Dakota Gov. Kristi Noem, a Republican, has taken a "hands off approach" to Covid-19 mitigation, wrote the IZA report's authors. Noem bragged about the Mount Rushmore State's low Covid-19 infection rate in a tweet on August 10.

A staunch supporter of President Donald Trump, Noem spoke last month at the Republican National Convention, where she railed against Covid-19 mitigation efforts including social distancing and mask-wearing, saying, "We are not--and will not--be the subjects of an elite class of so-called experts."

As "Sturgis" trended on Twitter Tuesday, Noem called the IZA report "fiction":

As of Tuesday, South Dakota was second only to neighboring North Dakota in coronavirus cases per 100,000 people, according to the New York Timesdashboard. The United States continues to lead the world in Covid-19 cases and mortalities, with more than 6.5 million reported cases and nearly 194,000 deaths.

The state's congressional representatives have hardly commented about the Sturgis rally at all on Twitter, and both Noem and Republican Sen. John Thune this week posted photos of themselves at the South Dakota State Fair--an event that drew more than 200,000 people last year--which was held over Labor Day weekend.

Echoing Clayton's dismissive sentiment about the IZA report, South Dakota Secretary of Health Kim Malsam-Rysdon told reporters Tuesday her department wants to "better understand the source they are using" to come up with the $12.2 billion healthcare cost total, adding that people "shouldn't put too much stock into models" and that using cell phone pings to project Covid-19 cases isn't an accurate correlation.

Friedson responded to critics on Twitter Tuesday.

"A lot of people (or maybe bots?) have accused my co-authors and I of having a political agenda with this paper," Friedson tweeted in a thread.

"I would encourage anyone with this take to see our respective research records," he continued. "My work, and that of my collaborators has come down on many different 'sides' of many different important policy issues. We go where the evidence leads us."