In modern society, occupational asthma is the most frequently occurring work-related respiratory disease. Occupational asthma is defined as a form of asthma that is generally caused by immunological sensitisation to a (specific) agent inhaled at work. A large – and growing – number of causative agents have been identified. These occupational ‘asthmogens’ may be macromolecules of biological origin, metallic agents or synthetic chemicals. Examples are listed in chapter 7. Inhaled irritants can also cause asthma without specific sensitisation, either after a single acute inhalation accident (RADS) or through repeated or chronic exposure to excessive levels, for example during cleaning work. In the latter case, the presentation of occupational asthma may resemble that of allergen-induced occupational asthma because the worker may have been able to work for some time without experiencing respiratory symptoms (i.e. there has been a symptom-free latency period). ‘Asthma-like’ disorders without evidence of sensitisation are also found in workers exposed to (endotoxin-contaminated) vegetable dusts (e.g. byssinosis in cotton workers, asthma-like syndrome in swine confinement workers).
In addition to asthma that is caused, more or less clearly, by work, many asthmatics also experience a worsening of their asthma caused by their working circumstances – so-called ‘work-aggravated asthma’. It has been estimated that one in seven severe asthma exacerbations is associated with work-related exposures.
Occupational asthma often has a poor prognosis, even when exposure has ceased, and it leads to considerable socioeconomic consequences, even in countries that have adequate provision for compensating workers with occupational diseases.
The population-attributable risk of work-related exposure has been estimated to be approximately 17% of all adult asthma cases, equivalent to an incidence of new-onset occupational asthma of 250–300 cases per 1 million people per year. According to occupational disease registries and voluntary reporting schemes in various European countries, the annual incidence of occupational asthma has been estimated to be 2–5 cases per 100 000 working individuals. Thus, occupational factors play an important role not only in causing specific occupational asthma but also in favouring the development of asthma in adults. Given the high frequency of asthma in the population, occupation represents a potentially important area of prevention. The costs of occupational asthma to society are high, and in most countries the economic burden falls on the state and the individual, not, or hardly ever, on the employer. The incentive for preventive action by employers is therefore weak.