COVID-19 Clusters and Outbreaks Among Non-Health Care, Noncongregate Workers in Chicago, Illinois: Surveillance Through the First Omicron Wave.

OBJECTIVE:To describe COVID-19 investigations by a large urban health department among non-health care, noncongregate 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, 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 one 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.