Study population and setting
In February 2021, the Illinois Department of Public Health and local health department conducted an investigation of an outbreak associated with an opening event at a rural Illinois bar. The event was held indoors in a 2800 square foot bar with limited ventilation. Cases associated with the outbreak were defined as COVID-19-like symptoms or a positive SARS-CoV-2 nucleic acid amplification test (NAAT) or antigen test within 14 days of the event. Cases could have been among attendees or employees who were at the event and reported no other known COVID-19 contacts. Secondary cases tied to the outbreak were defined as close contacts of the cases with a positive SARS-CoV-2 NAAT or antigen test. Interviews were conducted among all cases, both primary and secondary.
Summary of Main Findings
The total number of people who attended the event is unknown (the venue accommodated approximately 100 people), but there were six employees present. There was a total of 46 cases identified as linked to the event, including 26 attendees, three employees, and 17 secondary cases. At the event, there was one asymptomatic individual who had had a previous COVID-19 diagnosis from the day before, along with four people who had COVID-19 symptoms. Among attendees, it was reported that mask use was inconsistent and physical distancing of more than 6 feet apart was not adhered to during the event. There were 71 close contacts identified, of which 37 received testing (37/71, 52.1%). Among those who were tested, 46% received a positive result (17/37). Transmission associated with the event resulted in one school closure and one hospitalization of a long-term care facility resident.
The use of contact tracing data allows us to understand the real-world implications of limited mask use and lack of consistent physical distancing.
Because it is unknown how many people actually attended the event and because all close contacts were not tested, these numbers could be an underestimate of the total number of cases associated with the event. The cases identified are likely related to the bar opening event, but sequencing was not conducted and it is possible that the source of infection originated elsewhere or that there were multiple sources of infection.
This study builds on the evidence that when community transmission is relatively high, indoor events with poor mask use and limited physical distancing can lead to outbreaks.
This review was posted on: 7 May 2021