Two Types of Occupational Asthma

Immunologic asthma develops after a variable period of time during which "sensitization" to an agent present in the workplace takes place. Irritant-induced asthma occurs without a latency period after an intense exposure to an irritating dust, mist, vapor, or fume. The pathophysiologic mechanism underlying irritant-induced asthma is not well understood, and it is not known why the asthmatic response persists in certain individuals.¹

Two Types of Immunologic OA

The Haz-Map database focuses on immunologic asthma and the predictable and preventable occupational settings in which exposures occur. Immunologic asthma can be classified into that caused by high-molecular or low-molecular weight compounds. The high-molecular-weight compounds are animal and plant derived proteins or polysaccharides such as wheat flour and animal dander that cause an Ig-E-dependent  immune response. The low-molecular-weight compounds are chemicals that can also initiate an immune response after repeated inhalation. The nature of the immune response is more complex for the low-molecular-weight chemicals than it is for the high-molecular-weight agents. "An IgE- or IgG-dependent mechanism has not been consistently seen with low-molecular-weight agents (isocyanates, for example). These agents can cause sensitization through a hapten-mediated effect. The role of lymphocytes or other immunologic mechanisms remain unclear."²

The Haz-Map database contains over 180 biological agents and chemicals that can cause immunologic OA based on a previously published table. (Chan-Yeung & Malo and Appendix B in Harber) In the two tables that follow, the high-molecular-weight compounds and wood dusts are listed as "Biological Agents," while the low-molecular-weight compounds are listed in the "Chemicals" table. Wood dusts are biological agents or products, but sensitization may occur through a low-molecular-weight chemical, as has been proven for the case of Western red cedar.

Incidence and Prevalence of OA

In a study done in the West Midlands Region of the United Kingdom, the average annual incidence of occupational asthma was found to be 43 cases per million workers, with a range of 1833 per million for spray painters to eight per million for clerks.³

^{The prevalence of occupational asthma in adults with asthma is estimated to be between 3% and 20%.}

Prevention of Occupational Asthma

The diagnosis of occupational asthma is a sentinel event--an alert that engineering controls or protective equipment could prevent asthma from developing in workers in the same workplace or industry.

References:

1. Balmes JR. Occupational Lung Diseases. p. 315 in LaDou
2. Malo JL, Cartier A. Occupational Asthma, p. 424 in Harber
3. Gannon PF, Burge PS. The SHIELD scheme in the West Midlands Region, United Kingdom. Br J Ind Med 1993 Sep;50(9):791-6. Read Shield reports at the website of the Oasys research group.
4. PubMed Abstracts
5. See Table 2 from page 6 in Asthma in the Workplace.
6. Diagnosis and management of work-related asthma: American College Of Chest Physicians Consensus Statement