Occupational Asthma

by Dr. Noel Kerin - May 23, 2014

Occupational asthma (OA) is a serious and sometimes fatal illness; it is a growing problem in many Canadian workplaces. A very wide range of chemicals, and agents of biological origin, has been described as causes of OA. The costs to the worker and the employer are significant but preventable. Advances in effective management of asthma bring new hope to the employer when attempting to handle this chronic disease effects on their workers and the workplace. About 10% (5-15%) of asthma cases are occupationally caused. The proportion of asthma cases attributable to workplace factors may be as great as 28% (US National Institute for Occupational Health and Safety, 1996).

Half of all asthma cases are said to be not controlled properly.

What is Occupational Asthma?
Occupational asthma is a breathing (respiratory) disease caused by exposure to a trigger in the workplace. It is a chronic (long-term, ongoing) inflammation of the breathing passages (bronchi) of the lungs and often also involves the nasal passages. The inflammation irritates the airway, causing breathing problems.

• Most people with asthma have sudden attacks or periods of bothersome or severe symptoms separated by periods of mild symptoms or no symptoms at all.
• Asthma is an inflammatory reaction that is triggered by external factors or specific situations.
• When a person with asthma is exposed to one of his or her triggers, the inflammation worsens and symptoms ensue.

Occupational Asthma Facts
OA has become the most prevalent occupational lung disease in developed countries. Asthma, both occupational and non-occupational kills approximately 500 people in Canada each year (Health Canada) and according to the Workers Safety and Insurance Board of Ontario (WSIB) OA causes approximately two cases of lost time claims per working day in Ontario (400 per year). These are likely but the tip of the iceberg of actual OA cases.

OA is a common disorder that may be caused by several hundred agents (250+ and counting). The key to diagnosis is a high index of suspicion for the condition. Several readily available tests can be used to confirm the diagnosis. Many patients suffer from continued asthma despite cessation of exposure; early diagnosis and early removal from exposure are the most important factors for improving the long-term outcome.

OA can be either induced (caused by agents in the workplace or aggravated by agents in the workplace). Level of exposure is an important risk factor, and reduction of exposure is the only certain method of prevention. Atopy (hay fever, allergies) and smoking are further risk factors.

Asthma, whether it be caused by the workplace or not, is the same condition and causes a group of symptoms, which range from stuffy nose and cough to full-blown, life-threatening shortness of breath. Some people are ‘born with asthma’, and this is described as a genetic tendency to asthma. Studies now show that people born with asthma or who developed asthma in childhood, are more likely to develop allergic type asthmatic symptoms when exposed to asthmogenic agents in the workplace.

How is Occupationally-Induced Asthma caused?
Researchers have shown that a specific type of white cell (T-lymphocyte) becomes sensitized to a foreign agent, so that when this agent is again introduced to the person, a reaction occurs in the nasal passages and bronchial tree, which we understand to be asthma. This hyper-sensitivity reaction is, at present, a chronic disease with no cure. There are, however, very successful management systems for this condition.

Agents that cause asthma in the workplace do so in one of two ways:

1. Direct irritation of the respiratory tract tissues which is called reactive airways dysfunction syndrome (RADS) or irritant asthma, e.g. Chlorine gas, from mixing janitorial agents incorrectly or releases in the pulp and paper industry; and
2. Through an allergic pathway. This is the commonest type of occupationally-induced asthma. The asthma agents vary from very small molecules (Isocyanates), to very large molecules (red western cedar dust), as well as all sorts of various chemical agents in between. More recently researchers, including Dr. Susan Tarlo and her group in Toronto, recognized that some of the smaller molecules, such as Isocyanates, may actually sensitize a worker through the skin. This could explain why some workers develop an asthma response when coming in contact with chemicals while wearing appropriate respiratory protection.

Economic Burden of Occupational Asthma
The economic cost of asthma is very significant. Because it can be a life-threatening illness, parents become extremely concerned when a child has an asthmatic attack. This affects the workplace as both a problem with presenteeism (at work but not producing the usual amount and/or quality of work) and unavoidable parental absenteeism. When a child is admitted to hospital the average length of stay is five days, removing the child from school for at least one week at a time. This can have long-lasting effects as children who have chronic illnesses are known to perform less-well academically than those who are not afflicted with a chronic illness, such as asthma.

The cost of OA, likewise, has very serious implications. Firstly, for the life and health of the worker; as OA too, can be fatal. When a worker cannot breathe freely, their productivity suffers and, from various studies we know that approximately half of all asthmatics are poorly controlled. This, in turn, creates a significant presenteeism effect. When the disease becomes more difficult to manage, the employee loses time from work, creating further economic loss for both employee and employer. A quick calculation for the cost of absenteeism is: base pay x 2-5 times x days lost due to lost production/replacement costs. Presenteeism is not easily measured but in the USA it is commonly assigned a value of 2 times absenteeism!

How does an Employer Suspect an Employee is Suffering from Occupational Asthma?
A high index of suspicion is required to monitor for the development of OA in a worker. In the employee, frequent bouts of sneezing, stuffy nose, coughing, wheezing or shortness of breath when exposed to the workplace may be symptoms of an asthma problem developing. Conversely, workers may in fact develop early morning (e.g. 3-4 am) symptoms of asthma, making the connection between an asthma agent exposure in the workplace and the asthma condition difficult to connect. In other workers there may be a definite week-to-weekend variation in symptoms, so that a person may feel completely free of symptoms of nasal stuffiness, wheezing and coughing towards the end of a weekend and, in particular, a long weekend, than they do after being exposed day-by-day during the working week. Approximately half of all OA cases present first as an allergic rhinitis or hay-fever (recurrent sinus infection, nasal stuffiness and sneezing).

Finally, some workers will explain how they can reduce or withdraw all asthmatic medications when on an extended leave from the workplace, such as annual vacations.

All of these presentations of asthma in the workplace require careful consideration, vis-à-vis placement of the worker and various accommodation requirements under law. When faced with these difficult decisions, employers are well advised to seek counsel from an occupational health practitioner familiar with their work-type practices and the management of OA. In spite of the enormous amount of research that has gone into understanding asthma, including OA, much remains to be learned.

Specific Causes of Occupational Asthma
No job is immune from OA. We cannot mention all the causes here but we can highlight some of the commonest. In Ontario Isocyanate exposure from the automotive parts manufacturing and painting industries are the most common cause. In British Columbia western red cedar dust is a major problem, while the East Coast struggles with ‘crab asthma’ from working with crabs and other similar fish. Baker’s asthma is a problem wherever there is exposure to flour dust. Welders’ smoke and metal cutting fluids, colophony fume, from soldering especially in the electronics industry, cause frequent cases of the illness. Laboratory workers who handle animals and health care workers who use latex gloves are at risk of developing allergic asthma.

Indoor air quality is a growing issue when dealing with OA. Indoor air quality is influenced by poor air exchanges/unit of time (stale air), house mite droppings and other dust; by off-gassing of volatile organic chemicals (VOCs) from carpets, furniture, fragrances, perfumes and mould growth. Mould is a form of fungal growth that gives off a ‘perfume’ or toxin (mycotxin) when growing. Some toxins are known to cause allergic reactions in humans including asthma, e.g. Stachybotrys Chartarum, Penicillium Marneffei and Aspergillus Fumigatus. Mould needs three conditions to grow: moisture, warmth and food, e.g. cellulose such as found in ceiling tiles, paper and wood. Workplace floods, roof leaks, toilets and damp basements are typical breeding grounds for this type of mould problem.

How Can Employers Manage Asthma in the Workplace?
There have been several excellent management models developed by the Asthma Society of Canada, which show a very sound return on investment by an employer, of between three and seven times the invested dollar. In manufacturing, every effort at engineering out asthmogenic agents from the workplace has been shown to be beneficial. Where not possible, then strict engineering and administrative controls have been shown to effectively reduce the attack rate of asthma in the workforce.

In manufacturing plants where chemicals, such as chlorine and sulphur oxide products are used or manufactured, careful attention should be given to personal protective equipment (PPE) so that sudden high-dose exposure to these chemicals does not occur.

Today’s work environment is a challenge to both the worker and employer. We have new chemicals coming on stream that have not been tested for human safety. What about nanoparticles’ lung effects and how they carry other chemicals? What about combined effects of low dose chemical exposures which individually register under legislative chemical exposure guidelines in the workplace? What about the long term lung effects of OA. At this time, OA has been studied for about 30 years. It may take longer yet to see an evolving pattern of permanent lung damage.

Occupational Asthma Management
The most effective means of control is to prevent exposure altogether, either by not doing the task in question or by substituting the sensitizer agent for a less harmful material, although this is not always feasible. For example if a di-isocyanate based paint or varnish is being used, one should question whether a much less hazardous paint which simply dries out without curing can be applied instead.

Early removal from exposure increases the likelihood of recovery.
Continuous exposure in affected workers is associated with worsening of asthma.

Unfortunately, well-established asthma in many patients progresses in the absence of known further exposure, or perhaps does so because of increased sensitivity (reactivity) to undetected low-level exposure to the causative agent. Low level exposures at the workplace still may not allow affected employees to return to work because people with occupational asthma tend to react to extremely low concentrations of an agent.

The duration of symptoms before removal from exposure is a prognostic indicator irrespective of the agent.

Pulmonary function testing is a cornerstone in diagnosing occupational asthma. In cases where there is early or poorly defined symptoms a Methacholine ChallangeTest may help better define, if in fact, a workers’ lungs have become sensitized to a chemical. At this time there is no reliable blood test for OA. For the worker who in being investigated for OA or who is being reintroduced (accommodated) into the workplace, serial peak flow meter reading can help in emonstrating success or recurrence of the asthmatic condition.

As a large number of asthma suffers, including occupational asthma, achieve, at best, fair control of their condition, education is now considered to be an essential component of a successful management program. Also, newer understanding of the underlying mechanisms of causation and more effective medications has brightened the outlook for those who are unfortunate enough to have contracted asthma.