Occupational Diseases

Occupational diseases are disorders of health resulting from conditions related to the workplace. They are distinguished from occupational injuries, which are disorders resulting from trauma such as strains or sprains, lacerations, burns or soft-tissue injuries such as bruises.

Occupational Diseases

Occupational diseases are disorders of health resulting from conditions related to the workplace. They are distinguished from occupational injuries, which are disorders resulting from trauma such as strains or sprains, lacerations, burns or soft-tissue injuries such as bruises. In general, occupational diseases are related to exposures to physical, chemical or, controversially, psychological hazards; they usually develop over a period of time and often resemble or duplicate diseases occurring in other settings. By comparison, occupational injuries are mostly the immediate result of mechanical factors such as lifting or bending, or failures in safety measures resulting in accidents or fires. In practice, the dividing line is rather arbitrary (eg, established because of administrative convenience): certain types of injury, such as tendonitis resulting from repetitive movements, are counted as "diseases," and certain types of what would normally be considered a disease, such as acute poisoning by chemicals discovered immediately, are counted as "injuries."

Occupational diseases often develop over many months or years, depending on the intensity and circumstances of exposure. Cancer resulting from inhalation of ASBESTOS fibres, for example, generally takes at least 20 years to develop, and when it does develop it is difficult or impossible to identify the exact cause in the individual patient. Occupational diseases often resemble other medical conditions; for example, LEAD poisoning duplicates the symptoms of several illnesses, and asthma resulting from sensitization to chemicals in the workplace is often falsely attributed to exposures at home. For these reasons, most occupational diseases are often overlooked or misdiagnosed and are undercounted in statistical reports. They are more common than is generally realized.

Significance of Detection

The importance of recognizing a disease as occupational in origin is 3-fold: to limit its effect on the patient; to prevent its occurrence in others; and to compensate those disabled by it. Toxic effects can often be limited if exposure ceases and treatment is started early. When a worker is recognized as having an occupational disease, others exposed to the possible cause can be protected before they, too, develop the illness. Compensation is the role of the WORKERS' COMPENSATION systems in all provinces and among employees of the federal government.

Mandatory Insurance Systems

Workers' Compensation is a system of no-fault mandatory insurance against injury to employees required of all employers in business and industry above a certain size. It was set up in order to avoid the necessity of frequent lawsuits between workers and employers and to promote fair compensation to injured workers. Occupational diseases present difficult problems for workers' compensation boards compared to the relative ease by which injuries are handled. As noted, recognition of an occupational disease is often delayed and uncertain, and may be disputed in a given case, requiring the opinion of expert consultants. Provincial boards vary in their acceptance of certain types of claims. Proving a case generally means demonstrating that the patient has the disease, was exposed on the job to a substance or to conditions known to cause it, and had no other likely cause.

Virtually every board in Canada would accept any of the 29 groups of occupational diseases recognized by the International Labour Organization as being work-related, but acceptance of less well-established conditions, such as suspected but not proven causes of cancer, would vary among the boards. Few, if any, would accept highly speculative or unproven work-related causes of illness as the basis for a judgement. On the other hand, many boards have found it so difficult to sort out cancer due to cigarette smoking from that due to occupational exposure that they routinely disregard smoking as the most likely cause in cancer patients known to have been exposed to cancer-causing chemicals in the workplace.

Breadth of Occupational Diseases

Certain occupational diseases occur exclusively in certain industries or occupations; these are often given fanciful names such as welder's flash (an inflammation of the eye caused by ultraviolet light from welding) or farmer's lung (an inflammatory lung disease caused by inhalation of mold spores). Others occur in almost every industry, such as low back pain (more properly considered an injury) and noise-induced hearing loss. About half of all occupational diseases are skin disorders, followed in order by eye disorders, lung disorders, poisonings involving the body as a whole (as by lead, MERCURY or pesticides), and other conditions including disorders of the nervous system, heart and musculoskeletal system. Psychiatric and stress-related disorders are very controversial because a clear relationship to work is very difficult to prove.


The history of occupational diseases is as old as organized economic activity. Back pain resulting from strain at work is described in an Egyptian papyrus dating to at least 1600 BC. Other occupational disorders were prominently mentioned by Hippocrates in 460 BC and by Roman authors. In the Middle Ages and early Renaissance, several medical treatises were written on the hazards of mining and smelting.

The Modern Era

The modern era of occupational medicine dates from the early 1700s, when the great Italian physician Bernadino Ramazzini wrote the first comprehensive textbook in the field. Charles Thackrah wrote the first such book in English in 1831, during which time unprecedented and extensive legislation was being enacted in Britain to protect the health of workers, to control CHILD LABOUR, and to protect the public health at a time of rampant pollution and adulteration of food. These laws formed the basis for Canadian legislation before Confederation, and occupational health and workers' compensation are provincial responsibilities under the terms of the Constitution.

In 1914, workers' compensation, patterned after the German system, was introduced into Canada in Ontario. In the 1920s, Dr J. Grant Cunningham founded the Industrial Health Branch in the federal government and through research, education and demonstration promoted the concepts of prevention and early recognition of occupational diseases to industry and to provincial governments. His pioneering work led to many changes and to the training of a generation of occupational health professionals who influenced the practices of Canadian industry and provincial governments. Best known of these was Dr Ernest Mastromatteo of Toronto, who has been prominent for many years in national and international affairs related to the prevention of occupational diseases.

Leadership by Canadian Physicians

Canada has long been a leader in research on occupational diseases, particularly occupational lung diseases. Sir William OSLER, considered by many to be the greatest and most influential physician Canada has yet produced, wrote extensively on various occupational diseases; in 1876, he wrote a paper on coal workers' pneumoconiosis (often called "black lung") that first brought him to the attention of colleagues in Montréal. Cunningham was particularly interested in silicosis among miners in Ontario. Dr Frederick BANTING, better known as one of the discoverers of insulin, made many contributions to research on silicosis and to aviation medicine.

Interest in occupational diseases in major centres of research tends to be stimulated by economically important problems in local industries. Because of its importance to Québec, studies of asbestos and its health effects have been the principal focus of research at institutions in that province. In Ontario investigators have had particular interests in the mining industry. In BC, occupational causes of asthma and disorders of the flow of air in the lungs have been a major emphasis because of an unusual and common pattern of asthmatic reaction typical of responses to western red cedar, an economically important wood.

All physicians treating adults should have some concern for occupational diseases, whether in treatment or diagnosis or for the implications of certain exposures on the health of their patients. This is because occupational disorders may affect any organ system, may be the cause of unrecognized disease after retirement and occasionally affect other members of the family if chemical exposures are brought home inadvertently or through associated reproductive toxicity. In Canada, physicians may qualify by special training and examination to be specialists in the field of occupational medicine and to be so certified, either by the Royal College of Physicians and Surgeons of Canada if they complete a formal fellowship training program, or by the Canadian Board of Occupational Medicine if their preparation is otherwise. The national organization of occupational physicians is the Occupational and Environmental Medical Association of Canada.

A Shared Field

Although physicians play an important role in the diagnosis, treatment and certification for compensation due to occupational diseases, this role is shared by occupational health nurses (a specialized nursing field). The critical role of prevention is even more of a team effort, shared by physicians, nurses, safety officers, occupational hygienists (an engineering field of specialization) and several other professionals. All occupational diseases - without exception - are preventable. The obstacles to prevention are usually cost, lack of education and lack of motivation to change practices. The technical means to solve a problem are almost always available. Success in prevention ultimately rests on acceptance by the employer of one's responsibility, co-operation by the workers, teamwork by occupational health professionals, government regulation and education of the public.

Further Reading

  • Tee L. Guidotti, John W.F. Cowell and Geoffrey G. Jamieson, Occupational Health Services: A Practical Approach (1989); Barry S. Levy and David H. Wegman, eds, Occupational Health: Recognising and Preventing Work-Related Disease, 3rd ed (1995); William N. Rom, ed, Environmental and Occupational Medicine, 3rd ed (1998).

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