OA is a disease characterized by variable obstruction of airflow and/or airway hyperresponsiveness attributable to factors associated with the workplace rather than to stimuli found outside that environment. (Nicholson, 2002)
This requires a period of time for sensitization to the causative agent to develop, and therefore, there is a latent period between exposure and the appearance of symptoms. The following subtypes are distinguished according to the substances responsible for causing the disease: - Immunologic OA caused by high molecular weight substances. This usually occurs via an immunologic mechanism involving immunoglobulin (Ig) E. - Immunologic OA caused by low molecular weight substances. In this case, there is generally no clear involvement of IgE. (Anees, 2004)
This type of OA occurs as a result of irritation or toxicity. Two subtypes can be distinguished: - Reactive airways dysfunction syndrome (RADS). This is caused by single or multiple exposures to high doses of an irritant. Its onset, however, is linked to a single exposure. It is also known as OA without a latent period, since the symptoms appear within 24 hours of exposure. - OA caused by low doses of irritants. This occurs after repeated contact with low doses of the causative agent. ...
It is a condition of particular current relevance but that is still under discussion.
3. Other variants of OA.
This category includes OA with special or distinctive characteristics: - Asthma-like disorders. These are due to exposure to plant-derived dust (grain, cotton, and other textile fibers) and also to dust from confined animals. - Potroom asthma. This occurs in workers involved in the production of aluminium.
Prevalence and Incidence
Notable discrepancies are found in the data on prevalence and incidence currently available in the medical literature. Differences in the design of epidemiologic studies, the definition of OA, the study population, and the country in which the study was performed account for some of the discrepancies and the consequent difficulty in making comparisons. Some of the data can be found in a recent review article. It has been reported that 4% to 58% of all cases of asthma may be occupational in origin. A recent review of the literature estimated a mean value of 15%. Immunologic OA caused by high molecular weight substances is the most common form. (Anees, 2004)
The prevalence of the disease varies depending on the causative agent and it has been shown to occur in 4% to 12% of animal laboratory workers, 79% of bakers, and 1% to 7% of health care workers exposed to latex. The prevalence of OA caused by sensitization to low molecular weight substances is less clear, although some authors estimate it at around 40% of all cases of OA. The agents most frequently implicated in the disease in industrialized countries have generally been the isocyanates, which cause asthma in 2% to 10% of workers. (Nicholson, 2002)
In British Colombia, Canada, where the wood industry is very extensive, another agent, cedar wood, is more common and is