Researchers at Johns Hopkins University are raising doubts about a study that estimated that a massive motorcycle rally in Sturgis, South Dakota, last month led to more than 260,000 new cases of coronavirus nationwide.
The study, released late last week by four economists associated with the Center for Health Economics and Policy Studies at San Diego State University, also found that the annual event resulted in more than $12 billion in health care costs stemming from the infections.
The study has drawn considerable public attention in part because it seemed to confirm concerns expressed by health officials prior to the rally — which drew nearly 500,000 attendees over 10 days — of such a large gathering. The San Diego center's research also appeared to show a much larger coronavirus outbreak due to the Sturgis event than other sources. The Associated Press reported finding just 290 cases of coronavirus among people who attended the event nationwide.
South Dakota Governor Kristi Noem, who declined to restrict the event despite concerns about spreading the virus, has derided the study as "fiction."
In a paper posted Friday, the Johns Hopkins researchers say the data collected by the San Diego center's economists (who represent three different universities) in fact support one main thrust of the study — that the Sturgis event led to a spike in COVID-19 cases in the county that hosted the rally as well as in surrounding areas.
"The case data show relatively stable trends prior to the event and clear changes around the event, with little reason to believe that the changes in cases could have been caused by anything but the event," the Johns Hopkins researchers write. "The overall conclusions that the Sturgis event caused a large increase in COVID-19 cases and infections are likely to be relatively robust to the specific statistical methodologies used."
But the paper also called the model used to reach the study's specific finding of nearly 267,000 new cases of COVID-19 nationwide "relatively weak." As a result, the San Diego study should be "interpreted cautiously."
The Johns Hopkins researchers point to several factors in seeking to temper the Sturgis study's explosive findings, including:
- The San Diego researchers didn't compare geographic areas that were hit by coronavirus infections from Sturgis with other nearby areas. For example, a county in Arizona was compared to counties in Maine and Hawaii despite significant differences in the populations and mask-wearing habits of the two areas.
- The Sturgis rally likely caused more people to get a coronavirus test given the numerous warnings before the event about the potential health risks. That increase in testing — not direct transmission from people at the rally — could explain the jump in reported cases.
- The method used to put a public health cost of $12 billion on the Sturgis rally is simplistic because it fails to reflect that the costs of treating people with COVID-19 can vary widely around the country.
"There is evidence in that paper that Sturgis increased infections across the United States," Elizabeth Stuart, a statistician and associate dean at the Johns Hopkins Bloomberg School of Public Health who helped review the San Diego center's study, told CBS MoneyWatch. "But do I believe that number is 200,000 or more? I am not sure."
Joseph Sabia, one of the co-authors of the San Diego study, said in an email before Johns Hopkins' assessment was published that he and his fellow authors stand by the research and their "entire body of rigorous scholarship on COVID-19."
"We believe our evidence is compelling that the Sturgis Motorcycle Rally was the cause of this spike," Sabia told CBS MoneyWatch. The Centers for Disease Control and Prevention "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."