Occupational asthma that is caused by workplace exposures, and work-exacerbated asthma that is preexisting or concurrent asthma that is worsened by workplace exposures or conditions are called together work-related asthma. A review of relevant literature concluded that 16.3% of adult-onset asthma cases are attributable to occupation. This is likely an underestimate of the true frequency. For example, it appears that many physicians take inadequate occupational histories from their asthma patients and do not refer suspected cases to occupational medicine or pulmonary physicians for additional evaluation. Occupational asthma agents include both sensitizers and irritants and can have a distinct immunologic response.

Workplace interventions to improve the status of workers who have occupational asthma either include early removal from exposure or reduction of exposure. Removal from exposure includes substitution of causal agents or complete removal from exposure. Reduction of exposure includes changing the work process; relocation of the affected worker to another work area with less exposure; implementation of educational programs designed to prevent or reduce exposure, and adaptions in personal protective equipment. However, the actual benefits of these interventions are still unclear. We identified an update of a relevant Cochrane review of 2011 that aimed to determine the effectiveness of workplace interventions for the treatment of occupational asthma (Henneberger et al 2019). In this review extensive searches were performed in several databases up to July 31, 2019.

The Cochrane review by Henneberger et al (2019)¹ is based on 26 non-randomized controlled before and after studies including 1,695 participants with occupational asthma. Sensitizers caused nearly all cases. The review focuses on the interventions of removal from exposure and reduction of exposure, which were compared with continued exposure. Outcomes were changes in asthma symptoms, lung function, and non-specific bronchial hyperreactivity between baseline and follow-up.

The studies reported on complete removal from exposure and reduced exposure. Reduction of exposure was achieved by limiting use of the agent, improving ventilation, or using protective equipment in the same job, by changing to another job with intermittent exposure, or by implementing education programs. The quality of the evidence is very low for all outcomes due to the lack of randomization. It is likely that the patients with worse symptoms were more often removed from exposure.

If nothing was done, and exposure continued, only 5.6% of the workers were without symptoms at follow-up. They had a further decrease in FEV1 % (forced expiratory volume in one second as a percentage of a reference value) of 5.4% during follow-up, and they had a further increase in non-specific bronchial hyperreactivity (NSBH) (standardized mean difference (SMD) = -0.18).

Care providers should balance the potential clinical benefits of removal from exposure or reduction of exposure with potential detrimental effects of unemployment.

Your patient is a 55 year old furniture factory worker who will certainly benefit from occupational health measures. It is best to follow the hierarchy of controls approach here.

First check if exposure can be eliminated and isocyanate can be eliminated from the production process. If that is not possible propose to have the worker transferred to another department without the exposure. If this is not possible, he will probably lose his employment, given his age and education with a subsequent decrease in income. Therefore, as a last resort, he might benefit from education and personal protective equipment as the review shows that there is still considerable improvement possible with these measures. Based on shared decision-making, he could be offered a one year trial period of improving his work environment, better use of PPE and education about preventing exposure while his symptoms and lung function is closely monitored. If the outcome is that these measures are not sufficient we have to decide that this worker cannot be replaced in this factory, despite the consequences for his income.

Prevention by good work environment, education and personal protective equipment could have prevented this situation.