PL02 OCCUPATIONAL HEALTH EPIDEMIOLOGY IN THE FACE OF DISASTER
Authors: Cherry Nicola 
Published: July 2024

Abstract

Introduction
Definitions of ‘disaster’ focus on events causing great damage, loss, or destruction: and include both natural occurrences such as floods and volcanic eruptions and events resulting from man-made failures or conflicts. Some definitions emphasize also that the event is sudden and unexpected, others that the society’s response capacity is overwhelmed. While there has been a great increase in publications in the broad area of disaster research, not all consider health aspects, many are case studies with little epidemiological content and rather few (before COVID-19) were of those exposed to the health effects of disaster through their occupation. Major exceptions include the impact on health of response and clean-up workers after the Deepwater Horizon marine oil spill and on first responders after the collapse of the World Trade Center. It is all too easy to think of other disasters which would have warranted equally focused investigation of immediate and long-term health effects, and of ways to prevent recurrence, including the Bhopal gas escape in India and the Rana Plaza garment factory fire in Bangladesh. More generally, occupational disasters may include events without an abrupt onset with only retrospective recognition of the insidious harm done, for example exposure to silica in tunnelling or drought bringing economic and mental distress to farmers. Few such disasters are limited wholly to workers but spill out also into the community. Two ships colliding in the harbor of Halifax, Canada resulted in the deaths not only of the seamen but throughout the city. The gas escape in Bhopal killed thousands of residents as well as workers. Equally, community disasters put at risk frontline responders seeking to minimize harm to the population, or to rescue those trapped or damaged. This presentation considers factors critical to the conduct of epidemiological studies of workers exposed during such disasters.

Materials and methods
In considering barriers, facilitators, and best practice for occupational epidemiology in disasters we will draw on experiences from two such events in Canada. The first is of a wildfire that led to the evacuation of a town in the north of Alberta (known as the Fort McMurray fire). The study was set up, and data collection began, within 2 weeks of the fire overwhelming the community in May 2016. Over the following months we recruited 1234 firefighters deployed to the fire and followed them for five years with clinical assessment of respiratory and mental health. The second is a cohort study of healthcare workers during the COVID-19 pandemic. Again, we recruited the first cohort members very soon after the first COVID-19 infection was confirmed in Canada, and extended recruitment to four Canadian provinces with a total of 4964 healthcare workers followed up from the early weeks of the COVID-19 pandemic to the summer of 2022. The focus of interest in these studies was the occupation group, the firefighters and healthcare workers but always within the context of the communities in which they lived and worked.

Results
As occupational health epidemiologists, our basic mission is to investigate occupational causes of ill-health and to demonstrate how such ill-effects might be mitigated. In normal times, without incipient or actual disaster, we might choose to design and carry out intervention studies, randomizing some groups of workers to conditions where exposure to a risk is controlled and others to normal practice, and comparing changes in key health indicators. Such a design requires a hypothesis, planning, measurements before and after exposure, randomization of exposure groups, high compliance and near complete follow-up. Imagine in contrast setting up an epidemiological study in the immediate aftermath of a natural or manmade disaster. Unless you are from a wealthy country that has foreseen the need to support such disaster research, you are very likely to be on your own during the first few days, making decisions that may profoundly affect the viability of any study you hope to carry out. Unless the disaster is with a workforce whose culture you know well and in which you have useful contacts, the learning curve will be very steep. Research will be the last priority for those trying to contain the impact of the disaster and access may be barred to those wanting to measure exposure. Indeed, you may have rather little idea of the exposure parameters that will be key or of how to measure them. It is likely you will have no immediate record of who was present or where they were at the time of the catastrophic event. You will not know where they have fled to find refuge. If there are illegal immigrants among the work force or those whose papers are not in order, they will rapidly become untraceable.
Research into workforces with formal structures may be less intimidating than with informal workers or those with low literacy. In the study we did of firefighters at the Fort McMurray fire we were able to access names and home fire services for those from Alberta who were deployed to the fire as structural, industrial or wildland firefighters. This meant that we had the huge advantage of a nominal list, although we could only contact them through their employer and collaboration was uncertain. Equally, for the study of COVID-19 in health care workers we were able to contact frontline workers through their professional organizations although for some of those less formally employed the official lists were incomplete and contact details less reliable.
It is well recognized that estimation of relevant exposures is a central challenge for disaster epidemiology, but this is essential if we are to understand and apply new knowledge from the disaster to protect the health of future workers. For both studies described here, self-report of exposures was central but we were fortunate in being able to supplement this by collection of biological samples. For the firefighters we collected urine samples immediately after deployment, using urinary 1-hydroxypyrene as a marker of exposure to polycyclic aromatic hydrocarbons, together with inflammatory markers in plasma. In this study we were also able to estimate the concentration of particulate exposure from monitoring stations and satellite imagery. For health care workers we were able to use blood samples to confirm infection with the SARS-CoV-2 virus and their response to vaccination. The collection and preservation of environmental and biological samples for later analysis may be key to understanding the relationship between exposures and health effects caused by the disaster, and ways to do this must be considered and implemented as early as possible.
Understanding of changes in health due to the disaster can be greatly helped by access to medical records both before and after the event. This may only be possible in societies with universal access to health care and with central records, but this allowed us to demonstrate increased medical consultations for asthma in firefighters and for mental distress in health care workers. Access to spirometry from routine firefighter medicals before and after the Fort McMurray fire was also helpful in demonstrating effects of exposure. A particular challenge arises when a new condition, such as Gulf Wat syndrome or Long Covid is associated with a disaster. In the absence of a clearly defined health outcome, a convincing demonstration of dose-response may be difficult.

Conclusions
Occupational health practitioners and epidemiologists have an obligation to study the effects of natural or man-made disasters on the workforce, either as leaders or collaborators. While we cannot necessarily prevent repetitions it behooves us to learn what we can from the chaos and distress implicit in the disaster. This will help prepare for the next calamitous event that may appear in different disguise but requires an immediate, appropriate, and thoughtful response, ideally with a team of experienced epidemiologists on standby, with seed funding and collaborations in place. There may be lessons to be learnt also for the improvement of working conditions during the more normal daily round. Mental health supports found to be effective in mitigating distress in healthcare workers during a pandemic may be of value in later times for healthcare workers struggling with manpower shortages. Data on the lack of access to respiratory protection for firefighters during a disaster may open the door to a change of culture going forward. Occupational health epidemiology in the face of disaster has many challenges, but special circumstances can bring about change, if the evidence is there.