COVID-19 Clusters and Outbreaks Among Non–Health Care, Noncongregate Workers in Chicago, Illinois

Objective To describe COVID-19 investigations by a large urban health department among non-healthcare, non-congregate workplaces, and the utility of surveillance methods over time. Methods Frequencies of workplace-associated clusters and outbreaks are described by workplace type, workforce size, and method of identification over time. Results From April 2020 through January 2022, n = 496 COVID-19 investigations identified 442 clusters (89%) and 54 outbreaks (11%). Frontline essential workplaces comprised 36% of investigations before, versus 15% after vaccine eligibility. Pre-Omicron, most investigations (84%) were identified through case interviews. During Omicron predominance, case interviews decreased dramatically and identified 10% of investigations. Offices (41%) and bars and restaurants (36%) were overrepresented, and only 1 outbreak was identified, given decreases in confirmatory testing. Conclusions Findings suggest that vaccine prioritization reduced COVID-19 burden among highest-risk workplaces, but surveillance methods likely became less representative over time.