Asthma affects about 7.5% of the adult population.[1,2] Work-related asthma, one of the most common conditions encountered in occupational disease,[3-5] comes in various forms and occurs when workplace exposures cause or aggravate respiratory conditions. 

Work-related asthma can be categorized as either occupational asthma or work-aggravated asthma (sometimes referred to as work-exacerbated asthma), and accounts for 5% to 20% of new adult-onset asthma.[1,3-5] Occupational asthma can be due to sensitization to one or more agents or irritants in the workplace. Asthma related to sensitization to a chemical in the workplace is referred to as sensitizer-induced occupational asthma. Through repeated exposure to potential sensitizers (often for months or years), workers can develop sensitization, and upon re-exposure, may experience asthma symptoms. Workers often report typical symptoms of asthma at the workplace, with improvement away from the workplace.

Exposure to an irritant, in the absence of sensitization, can also induce a form of asthma termed irritant-induced asthma or reactive airways dysfunction syndrome (RADS). The classic criteria for RADS include: 

• A history of new-onset asthma. 
• Symptom-onset related to a single high-level exposure.
• Onset of symptoms within 24 hours of exposure.
• Exposure to a high concentration of gas, fumes, or a spray-known irritant.
• Airway hyper-responsiveness or reversible airflow obstruction. 

Recovery can be prolonged (more than 3 months) or can lead to persistent asthma.[5] 

Work-aggravated asthma is pre-existing asthma aggravated or exacerbated by work exposure to irritants. 

More than 300 substances have been identified as being causally associated with asthma, the majority being sensitizers.[1,2,4] Common sensitizers seen in BC include plicatic acid (Western Red Cedar) seen in sawmill workers and diisocyanates seen in spray painters, chemical manufacturing, foundry, and other industries. For a list of agents associated with occupational asthma by occupation, visit www.csst.qc.ca/en/prevention/reptox/occupational-asthma/Pages/occupational-asthma.aspx.

Diagnosis

Asthma is a heterogeneous clinical syndrome primarily affecting the lower respiratory tract characterized by episodic or persistent symptoms of wheezing, dyspnea, and cough. The diagnosis of asthma requires these symptoms and demonstration of reversible airway obstruction using spirometry and/or methacholine challenge testing. A negative spirometry result does not necessarily exclude the diagnosis of asthma, and if clinical suspicion remains high, either repeat spirometry or methacholine challenge may be indicated.[1,2]

After a diagnosis of asthma has been made, the next step is to determine if it is work-related. Of note, spirometry testing may be negative away from the workplace/exposure. As a result, peak flow metres or spirometry testing may need to be completed in relation to the workplace to confirm the work relationship. Further testing to confirm sensitization may sometimes be required and may be carried out by specialists in occupational medicine. If you would like your patient to be seen by a consultant specialist from WorkSafeBC Occupational Disease Services, please indicate this on your Form 8/11 and an occupational disease medical advisor will be in touch with you.

A claim for asthma requires objective evidence such as that confirmed through pre- and post-bronchodilator spirometry, pulmonary function testing, and/or methacholine challenge testing. In the case of work-aggravated or irritant-induced asthma, with appropriate medical treatment and appropriate mitigation of work triggers, many workers can continue in their job. However, if occupational asthma is strongly suspected, particularly sensitization-related occupational asthma, removal from the workplace is the recommended course of action. If a worker is unable to continue working at their present place of employment due to work-related asthma and the claim is accepted, vocational rehabilitation is the next course of action. While fit-tested respirators may mitigate symptoms from irritants, even exposure to a small dose of a sensitizer, once sensitized, may produce symptoms and respirators may not be of benefit.

For more information or assistance

If you would like to speak with an occupational diseases medical advisor, or you have further questions regarding an asthma claim, please contact a medical advisor in your nearest WorkSafeBC office.
—Brian E. Ng, MD, MPH, CCFP
WorkSafeBC Medical Advisor

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This article is the opinion of WorkSafeBC and has not been peer reviewed by the BCMJ Editorial Board.

References

1.    McCracken JL, Veeranki SP, Ameredes BT, Calhoun WJ. Diagnosis and management of asthma in adults A review. JAMA 2017;318:279-290. 

2.    BC Guidelines. Asthma in adults – recognition, diagnosis and management (2015). Accessed 4 December 2018. www2.gov.bc.ca/gov/content/health/practitioner-professional-resources/bc-guidelines/asthma-adults. 

3.    Dykewicz MS. Occupational asthma: Current concepts in pathogenesis, diagnosis, and management. J Allergy Clin Immunol 2009;123:519-528; quiz 529-530.

4.    Rosenman KD, Beckett WS. Web based listing of agents associated with new onset work-related asthma. Respir Med 2015;109:625-631.

5.    Tarlo SM, Lemiere C. Occupational asthma. N Engl J Med 2014;370:640-649.