What research can do: Estimating the role of workplaces in COVID-19 transmissions

Published: August 25, 2020

By Dr. Cam Mustard, President and Senior Scientist, IWH

As Canada emerges from lockdown and larger numbers of workers return to their physical workspaces, the effectiveness of workplace practices to prevent COVID-19 transmission will become increasingly important. To anticipate the challenges ahead, we need to know the role that occupational transmission has played in the first six months of the pandemic.

Although most employers complied with emergency measures and shuttered their physical operations, by our estimates, more than 35 per cent of Ontario’s workforce remained at their workplace. Employers in a wide range of essential sectors—health care, emergency services, mining, transportation, construction, manufacturing, food production, distribution and retail—all had to manage the risk of occupational transmission.

What percentage of COVID-19 infections in the province were associated to exposure at work? Although there are gaps in important information, we can make an educated guess.

Here’s what we do know. In Ontario, two sources of information can be used to estimate the incidence of COVID-19 infections that arise from workplace exposure and transmission.

The first information source is the work done by public health officials to trace recent contacts of people who test positive for COVID-19. This contact tracing can identify transmission that may have occurred in workplace settings.

The second is the number of compensation claims registered at the Workplace Safety and Insurance Board (WSIB) by workers who test positive for COVID-19 and who believe they may have contracted the virus in a workplace setting. WSIB officials adjudicate individual claims to assess evidence for work-related transmission before allowing the compensation claim.

During the early period of the COVID-19 emergency in Ontario, from March to May, the 32 public health units in the province faced enormous challenges in completing timely contact tracing interviews with people who tested positive for COVID-19. With the exception of infections among health-care workers in hospitals and long-term care facilities, information on employment status, occupation and industry sector was not consistently recorded for cases among working-age adults.

In the same period, the WSIB established dedicated teams of adjudicators and claim administrators to evaluate compensation claims submitted by workers and their employers. As of early June, the WSIB began publishing the number of compensation claims attributed to COVID-19, tabulating the number of claims allowed, not allowed and pending adjudication within economic sectors.

By combining information from Ontario’s public health system and the WSIB, we can build a picture of the incidence of COVID-19 attributed to workplace transmission. As of the beginning of August, daily new cases in Ontario had fallen to about 100, from a peak of 600 daily cases in mid-April. Of the 40,000 confirmed cases between March and the first week of August, approximately 60 per cent (24,380) occurred among working-age adults (ages 20-59). As of the first week of August, the WSIB was reporting 4,507 allowed compensation claims, 966 not allowed, and 605 pending adjudication.

Using the number of claims allowed and the number of people infected who were of working age, we can conservatively estimate that a non-trivial 20 per cent of infections among working-age adults in Ontario can be attributed to workplace transmission.

Of the allowed claims, more than 70 per cent are associated with workers in the health-care system, though new infections among these workers have declined substantially. Agricultural workers in southwest Ontario experienced the highest burden of occupational transmission in the June to July period.

As health-care workplaces have increased access to required personal protective equipment and gained experience in safely caring for infected patients and residents, we should expect the incidence of infections to decline in this sector. Conversely, as more workplaces resume economic activity, we need heightened vigilance to reduce the risk of occupational transmission in all sectors. Poor workplace infection control practices could be an important factor in the size and spread of COVID-19 in the potential second wave.