Workplace assessments in Washington helped ID cases that would have been missed

Including workplace investigations in Covid-19 surveillance programs have the potential to extend contact tracing efforts and identify cases not previously tied to the workplace, according to a CDC investigation conducted in King County, Washington.

Washington state was home to the first U.S. case of Covid-19 in 2020, and King County itself saw the first SARS-CoV-2 related death and a number of early outbreaks that helped characterize the spread of Covid-19 before the pandemic was officially declared. To help fight back the tide of Covid-19, Public Health—Seattle & King County (PHSKC) established a Covid-19 workplace surveillance and response system to augment contact tracing efforts and identify local outbreaks.

The results from those investigations, Jesse Bonwitt, BVSc, and colleagues from the CDC and PHSKC explained, suggest that focusing surveillance efforts on workplaces can “serve as an opportunity to provide guidance on preventing workplace exposures to SARS-CoV-2, facilitate access to vaccines, and strengthen collaborations between public health and businesses.”

Their findings were published in the CDC’s Morbidity and Mortality Weekly Report.

For their investigation, Bonwitt and colleagues looked at workplaces that met their “investigation threshold”—one or more Covid-19 patients attending work while contagious or two or more Covid-19 patients from the same workplace reporting symptom onset or receiving a positive SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) or antigen test result within 14 days—from June 15 through Nov. 15, 2020.

The investigators classified workplaces as high, medium, or low priority based on information collected from Covid-19 patient interviews.

“Workplaces meeting at least one of the following criteria were classified as high priority: 1) workplaces with two or more laboratory-confirmed (RT-PCR or antigen test) Covid-19 cases in which symptom onset occurred within 14 days (or asymptomatic workers who received a positive laboratory test result); 2) workplaces with an infected person who mentioned coworkers had received positive test results or had Covid-like symptoms; 3) workplaces with an infected person without phone numbers for exposed coworkers or customers; or 4) workplaces in which at least one person with laboratory-confirmed Covid-19 infection reported going to work while contagious, and one of the following: a) at least five potential close contacts with other coworkers or customers, b) was an industry with a high number of customers or a high-density workplace, c) had a disproportionate number of workers at higher risk for infection or disproportionally affected or restricted populations, or d) had workers with concerns about an absence of infection control measures in the workplace because they worked in close contact with coworkers or customers,” the study authors wrote.

Medium-priority workplaces were those with at least one person with laboratory confirmed infection who reported attending work while contagious and one of the following:

  • Workers reported working in close contact with coworkers or customers.
  • Workers had concerns about an absence of infection control measures in the workplace.
  • Was an industry with a likely high number of customers.
  • Was a workplace with a prior documented Covid-19 outbreak or other concerns that were flagged during the case investigation.

Low-priority workplaces had at least one patient with laboratory confirmed infection who reported attending work while contagious and none of the other criteria for high- and medium-priority locations.

“A workplace investigation entailed working with occupational health services, human resources, or managers to identify all cases and contacts, assessing workplace adherence to Covid-19 prevention and control guidelines, and responding to outbreaks,” they explained. Medium- or low-priority workplaces were only investigated once all high-priority workplaces were assigned to investigators.

From June 15 through Nov. 15, 2020, a total of 2,881 workplaces met the investigation threshold—of the 2,850 with known priority levels, 1,770 (62.1%) were classified as high priority, 702 (24.6%) were medium priority, and 378 (13.3%) were low priority; a total of 1,305 (45.3%) of 2,881 workplaces were investigated.

“Among 1,305 (45.3%) investigated workplaces, 524 (40.3%) met the definition of a workplace outbreak,” they found. “Among 306 (58.4%) workplaces with complete data, an average of 4.4 employee Covid-19 cases (median=three; range=1–65) were identified per outbreak, with an average attack rate among employees of 17.5%.”

Importantly, among 191 workplaces with complete information on contacts, “workplace investigation uncovered an average of 2.7 contacts not previously elicited (median=one; range=1-35),” they added. “Among 507 workplaces with complete information on cases, an average of 0.5 cases not previously linked to the workplace (median=0; range=0–11) were identified. High-priority investigations were more likely than were medium- and low-priority investigations to identify two or more exposed workplace contacts not previously elicited, two or more cases not previously linked to the workplace, or two or more employee cases.”

The study authors concluded that workplace investigations should be widely incorporated into contact tracing efforts in order to identify workplace outbreaks and inform implementation of strategies to prevent the spread of Covid-19. What’s more, Bonwitt and colleagues argued that “prioritizing workplace investigations based on workplace and workforce characteristics gathered during patient interviews can optimize investigation timeliness and effectiveness in resource-constrained settings.”

Study limitations included that only half of workplaces were investigated, and most of those were high-priority, which could have biased the results; effectiveness data was missing for many workplaces; misclassification of workplace exposures and outbreaks may have occurred; and the relatively low proportion of cases associated with workplace outbreaks suggest potential underreporting of workplace-associated cases.

  1. Including workplace investigations into Covid-19 surveillance efforts helped to identify contacts and cases that would not otherwise have been identified, according to an analysis from King County, Washington.

  2. Focusing Covid-19 surveillance efforts on workplaces may serve as an opportunity to provide guidance on preventing workplace exposures to SARS-CoV-2, facilitate access to vaccines, and strengthen collaborations between public health and businesses.

John McKenna, Associate Editor, BreakingMED™

The study authors had no relevant relationships to disclose.

Cat ID: 190

Topic ID: 79,190,730,933,190,926,192,927,151,928,925,934