At least 86 COVID-19 cases, 1 death linked to motorcycle rally

At least 51 people in Minnesota developed COVID-19 after attending a 10-day motorcycle rally in the neighboring state of South Dakota, according to data published in MMWR.

Officials from the Minnesota Department of Health and CDC also identified 35 secondary or tertiary infections among household, social or workplace contacts of these cases. 

Altogether, 86 COVID-19 cases in Minnesota were linked to the rally. Among them, four patients were hospitalized, and one died.

“Approximately one third of counties in Minnesota reported at least one case epidemiologically linked to this event,” Melanie J. Firestone, PhD, of the MDH, and colleagues wrote. “These findings highlight the far-reaching effects that gatherings in one area might have on another area.”

The motorcycle rally was held in western South Dakota from August 7 to 16. About 460,000 people across the United States attended the event, according to Firestone and colleagues. There were no policies on event sizes or mask use in the state.

Before the rally, the MDH recommended through the media that attendees quarantine for 14 days after the event and undergo testing 5 to 7 days later, even if they did not show symptoms.

During an investigation after the rally, Firestone and colleagues identified 51 primary cases, 21 secondary cases and five tertiary cases that were confirmed to be associated with the rally. They also identified nine additional secondary or tertiary cases that were likely associated with the rally. Findings from whole genome sequencing analyses supported the secondary and tertiary transmissions. The one patient who died was a primary case.

Among all 86 patients, 74% were symptomatic, according to the researchers. The onset of symptoms among primary cases ranged from August 8 to 26. Two patients said they had symptoms before the rally, which they attended during their infectious period. Of 48 patients who were interviewed, 33% said they worked while infectious, including five who worked at the rally and four who worked in health care after the rally. Secondary cases were traced back to two workplace outbreaks, one wedding outbreak and one funeral outbreak.

Due to limitations of the study, including not being able to identify all case contacts, Firestone and colleagues said the findings underestimate of the impact of the motorcycle rally on COVID-19 transmission.

“Despite underascertainment of the rally’s full impact in Minnesota and other states, these findings highlight the importance of reducing the number of attendees at gatherings and emphasizing mask use, physical distancing, isolation for patients with COVID-19 and quarantine for close contacts as strategies for reducing the spread of COVID-19,” they wrote. “Furthermore, these findings demonstrate the rationale for consistent mitigation measures across states.”