The scope of this chapter is occupational disease cluster managementin Ontario.

The term “cluster” has been used in recent years to describe an unusual number of cancers occurring among a relatively small group of people that may be due to new and emerging hazards. OD clusters can include many diseases and may be identified when there is a perceived excess risk in a larger population that may be exposed to recognized hazards. The United States CDC defines a cluster as “a greater than expected number of cases that occurs within a group of people in a geographic area over a defined period of time.”

We will use clusters to describe a group of workers who may have an occupational disease related to workplace exposures. Cluster is being used to denote a group of workers with a problem. There are three types of clusters we will consider:

  1. Clusters may involve acute exposures and effects — inhalation injury, chemical burn.
  2. Chronic exposures and effects for workers still in the workplace — occupational asthma, occupational dermatitis.
  3. Long-latency illnesses when the workers may or may not be in the workplace, and, in some cases, the workplace and its records no longer exists — cancer.


It is noted that there are no legislative or regulatory requirements related to investigations of clusters other than potential infectious disease clusters that may fall under public health.

The following provides a brief synthesis of findings related to cluster management practices and research findings. We have defined various scenarios for the purpose of this discussion. There is no common language nor necessarily even understanding of these different scenarios.

For a group of individuals with acute symptoms, it is likely that they will seek healthcare by going to an emergency department if the problem is severe or their other care providers if the symptoms are not life-threatening. Depending on the severity of the exposure and disease, there is often an immediate investigation of the workplace (for example,  carbon monoxide poisoning). If the symptoms are not as severe, the cluster may continue, and its resolution may take some time.

Workers who have had exposure to workplace agents for a longer period of time (weeks to years) may gradually develop occupational diseases. In these cases, they are usually still in the workplace, and the key question is the diagnosis — what disease are workers suffering from? Obtaining a definitive diagnosis is key to understanding if it is, in fact, related to workplace exposures. Examples would be occupational asthma and dermatitis. In this instance, unless it is recognized that there are a number of people with what appears to be the same problem, it is likely that workers will seek care individually. If it is recognized in the workplace that there appears to be a cluster, the group may be investigated as a group.

The third type of cluster is those diseases that occur after many years of exposure. The workers may or may not still be in the workplace. In some cases, the company may no longer exist. Examples of diseases that would most likely fall in this group are cancers and chronic diseases. These workers are most likely to have been diagnosed by their own healthcare provider.


In the past, the Ontario Ministry of Labour had a group of dedicated staff with clinical, epidemiology and occupational hygiene who conducted sampling studies, looked at trends and informed prevention.

There was also collaboration between clinicians in the community and Ministry of Labour physicians.

The initial investigation of flock worker’s lung in Kingston was done by Kingston respirologists with the aid of Ministry of Labour physicians. Not only was the problem recognized, but the local specialist group followed the group of workers for a number of years, contributing to our understanding of the natural history of flock worker’s lung. Of interest, the identification of the cluster was aided by the fact that it occurred in a smaller city with one major hospital, so the workers were being seen by a small group of respirologists who would regularly see each other and discuss cases.

For clusters involving current exposures and needing specialized clinical diagnosis, the occupational medicine clinic at St Michael’s Hospital has undertaken this type of investigation. Examples include: a discharge of Halon 1301 in a fire extinguishing system, workers involved in demolishing a water treatment plant with lead exposure, two separate clusters involving workers with contact dermatitis related to epoxy exposures and two outbreaks of scabies in chronic care facilities, one of which spread to the community

A number of these investigations have been published.

OHCOW is investigating a number of historic clusters. Some of these are related to specific workplaces, and others apply across workplaces. The workers are suffering from not only cancer but a variety of other diseases.

Public Health Ontario investigates clusters. These are generally environmental (for example, environmental, school), but they may get requests related to the workplace clusters.

Consultation and review summary

Reports and reviews

An OCRC report on an approach to investigating clusters is being written. It is expected that the report will address the need for the MLITSD and other system partners to develop:

  1. collaborative approaches
  2. protocols and resources for an expeditious response

Stakeholder focus groups

Gap themes

  1. Cluster management process is unknown.
  2. There are many challenges with identifying clusters.
  3. There is a lack of resources to manage clusters.
  4. Managing clusters vs individual cases needs to be differentiated/clarified.

Solution themes

  1. Clarify protocol/process for investigating and managing clusters considering:
    • Differentiate between historic/long latency clusters and active emerging illness clusters.
    • Identify which health conditions to focus on first.
    • Ministry proactively investigates workplaces when hearing about a potential cluster.
    • Distinguish between the purpose of the process for claims/compensation versus healthcare and secondary prevention.
  2. Balance the use of epidemiological data with other data sources:
    • Consider different kinds of evidence fairly when evaluating clusters.
    • Bring data together from across MLITSD, MOH, MOE.
  3. Listen to and acknowledge the stories (don't leave workers, their families, and communities behind with no support or resources).
  4. Clarify roles and increase resourcing (who identifies, who investigates, who decides).

Summary review findings

  1. The term cluster has many meanings. There are also different purposes for investigating clusters.
  2. No one agency in Ontario is responsible for investigating occupational clusters; neither the WSIB nor the MLITSD has the necessary occupational hygiene, clinical or epidemiological research capacity.
  3. It is unclear who has the role or authority to launch a cluster investigation (for example WSIB, MLITSD, OHCOW, unions, worker and patient advocates so any or all may try).
  4. Unlike public health outbreaks, there is currently no formal protocol for OD cluster investigation and management in Ontario. Response to clusters remains primarily reactive.


System goals

  • Clear definition of types of clusters.
  • Clear understanding of the purpose of investigating various types of clusters.
  • Clarified roles, clear process steps, and standardized data capture for tracking and surveillance.
  • Improved transparency and communication with all concerned.

Short term recommendations

5.1 MLITSD and WSIB agree on cluster definitions, statements of purpose, and criteria for the identification of clusters. For this purpose, we are defining two different types of clusters.

  1. acute and long latency diseases
  2. long-latency, historic clusters

Implementation guidance:

  • MLITSD assign a team to draft definitions, statements of purpose, and criteria for cluster identification, considering the OCRC report on clusters that is under development
  • run a consensus meeting with a number of stakeholders to refine and agree
  • formally communicate
  • consider a one-time process to address the current cluster investigations underway

5.2 For acute and long-latency diseases where the potential for a work-related disease is present in a group of workers, but the diagnosis is unknown, and specialists are needed for diagnosis and management. In this type of cluster, there is the potential need for workplace intervention to control exposures and improve prevention.

  • establish an expert clinical task force to develop response protocols
  • establish a clinical response team (specialists as appropriate for the clinical presentation and supporting clinical staff) to investigate and provide specialized diagnostic services as needed (see Topic 6: Academic Hub)
  • develop a protocol involving the MLITSD and the OHS system partners to provide assistance to the workplace, particularly small and medium-size workplaces for the evaluation, and recommendations for controlling exposure and improving prevention

5.3 Long-latency, historic clusters where the diagnoses are generally known and the key question is the association with workplace exposures.

  • MLITSD assigns an expert task force to establish a protocol for accepting referrals, steps and methods of investigation, and steps in management, including:
    • investigation of cluster
    • worksite prevention support if needed
    • communication and outreach
    • administrative steps with the WSIB

Longer term recommendations

5.4 Develop an implementation plan and process for phasing in new cluster protocols.

5.5 Ensure cluster data is well linked with provincial surveillance system to inform sector-wide prevention efforts.