By Ken Stone
Days after San Diego State researchers released a report that 266,000 coronavirus infections could be linked to a South Dakota motorcycle rally, health officials threw cold water on the San Diego County impact.
“Two [infections] only,” said county spokesman Michael Workman on Wednesday. “Separate cases. No outbreaks.”
“The South Dakota Department of Health has reported 124 cases linked to the Sturgis rally through contact tracing,” said The Washington Post, whose own survey of health departments found an additional 204 rally-linked cases in 20 states.
The 60-page report, issued by German-based IZA (Institute for the Future of Work), was partly the work of Drew McNichols and Joseph J. Sabia, who wrote for SDSU’s Center for Health Economics & Policy Studies.
Their conclusions about the “superspreading event” — based on anonymized smartphone data from San Francisco’s SafeGraph Inc. and COVID-19 case data from the Centers for Disease Control and Prevention — led to pushback from South Dakota authorities.
South Dakota state epidemiologist Josh Clayton told the Post: “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.”
The report also said the Sturgis rally generated “substantial” public health costs nationwide, “which we calculate to reach at least $12.2 billion.”
Use of cellphone data also raised eyes in South Dakota.
Asked for comment on the South Dakota criticisms, Sabia issued a statement Wednesday: “We stand by our entire body of rigorous scholarship on COVID-19, including studies of President Trump’s Tulsa Rally, Black Lives Matter protests, the Wisconsin Supreme Court stay-at-home ruling and the Sturgis Motorcycle Rally. We encourage policymakers’ and the general public’s interest in scientific evidence and look forward to peer-review from fellow qualified experts.”
Perhaps anticipating the critique, the report said SafeGraph data from 45 million anonymized cell phones “have been used widely by scholars examining the impact of COVID-19 mitigation policies…. These data have been used commonly by the Centers for Disease Control and Prevention and other researchers to study social distancing behavior during the COVID-19 epidemic in the United States.”
Among their other findings: San Diego County was among 20 counties in the United States with the highest relative intensity of what they called Sturgis attendee inflow. (Los Angeles County was the only other one in California.)
Sabia told Times of San Diego that a motivation to study Sturgis was that the CDC has stated that large in-person gatherings of individuals who do not socially distance and who have traveled from outside the local area are at “highest risk” for COVID-19 spread.
“The Sturgis rally had all of these elements (on steroids),” he said via email. “Nearly a half a million individuals traveled from all corners of the United States to gather in a small town without any mask-wearing or serious mitigation efforts.”
Sabia said his team found strong evidence of COVID-19 spread not only in South Dakota, but also across the United States in hundreds of counties that contributed large inflows of attendees into the event.
“We estimate a 7% to 12% increase in COVID-19 cases in these counties, on average,” he said, and added: “Contact tracing studies are useful but costly and therefore non-comprehensive. We do not have universal contact tracing in the United States and thus are only able to capture a small share of total cases attributable to a superspreading event.”
He said data on individuals’ movements — such as anonymized smartphone data — and county-level COVID-19 cases were needed to assess the total COVID-19 effects of large in-person gatherings such as the Sturgis rally.
“While San Diego County was a ‘higher’ inflow county, we do not conduct separate analyses of the effect of Sturgis on coronavirus cases in San Diego County alone,” Sabia said.
The study said the Sturgis Motorcycle Rally represented a case 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,” the study said. “The only large factors working to prevent the spread of infection was the outdoor venue, and low population density in the state of South Dakota.”
SDSU’s Sabia, professor of economics and Director of the Center for Health Economics & Policy Studies, credited the Troesh Family Foundation and the Charles Koch Foundation for grant funding for the study.
Sabia joined IZA as a research fellow in April 2015, and his profile says his research interests are in the economics of risky behaviors, the economics of national defense and minimum wage policy.
He received a Ph.D in economics from Cornell University and also worked at the University of Georgia, American University, the United States Military Academy-West Point and the University of New Hampshire.
Updated at 3:55 p.m. Sept. 9, 2020
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