Workplace interventions to deal with occupational asthma

Clinicians and researchers have proposed several changes in workplaces to improve the status of workers who have occupational asthma, which is asthma whose onset is caused by occupational exposures. These workplace changes are also called interventions, and for occupational asthma include early removal from exposure and reduction of exposure. However, the actual benefits of these interventions are still unclear.

What is the aim of this review?

To determine the effectiveness of workplace interventions for the treatment of occupational asthma.

Key messages

We conducted a systematic review of workplace interventions for treating occupational asthma. Asthma symptoms and lung function may improve when persons with occupational asthma are removed from exposure, usually by ending their job, compared to continued exposure on the same job. Asthma symptoms but not lung function may improve after reducing exposure, for example by training and education, compared to continued exposure. Removal from exposure may improve symptoms and lung function more than exposure reduction among workers exposed to low molecular weight agents, but removal from exposure may also increase the risk of unemployment. All evidence was of very low quality and therefore there is a need for better studies to investigate the effectiveness of workplace interventions for occupational asthma.

What was studied in the review?

The review is based on 26 studies that included 1,695 participants with occupational asthma. Sensitizers caused nearly all cases. We focused 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.

What are the main results of the review?

Both removal from exposure and reduction of exposure may improve asthma symptoms when compared to continued exposure. Removal from exposure, but not reduction of exposure, may improve lung function when compared to continued exposure. Removal from exposure may improve symptoms and lung function more than reduction of exposure among patients exposed to low molecular weight agents, but removal may also increase the risk of unemployment. Consequently, the benefit of a better improvement has to be weighed against the potential for a higher risk of job loss.

Further research is needed to determine the effectiveness of interventions at reducing the impact of occupational asthma.

How up-to-date is this review?

We searched for studies that had been published through 31July 2019.

Authors' conclusions: 

Both removal from exposure and reduction of exposure may improve asthma symptoms compared with continued exposure. Removal from exposure, but not reduction of exposure, may improve lung function compared to continued exposure. When we compared removal from exposure directly to reduction of exposure, the former may improve symptoms and lung function more among patients exposed to low molecular weight agents. Removal from exposure may also increase the risk of unemployment. Care providers should balance the potential clinical benefits of removal from exposure or reduction of exposure with potential detrimental effects of unemployment. Additional high-quality studies are needed to evaluate the effectiveness of workplace interventions for occupational asthma.

Read the full abstract...
Background: 

The impact of workplace interventions on the outcome of occupational asthma is not well understood.

Objectives: 

To evaluate the effectiveness of workplace interventions on occupational asthma.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE (PubMed); EMBASE(Ovid); NIOSHTIC-2; and CISILO (CCOHS) up to July 31, 2019.

Selection criteria: 

We included all eligible randomized controlled trials, controlled before and after studies and interrupted time-series of workplace interventions for occupational asthma.

Data collection and analysis: 

Two authors independently assessed study eligibility and risk of bias, and extracted data.

Main results: 

We included 26 non-randomized controlled before and after studies with 1,695 participants that reported on three comparisons: complete removal from exposure and reduced exposure compared to continued exposure, and complete removal from exposure compared to 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. For continued exposure, 56 per 1000 workers reported absence of symptoms at follow-up, the decrease in forced expiratory volume in one second as a percentage of a reference value (FEV1 %) was 5.4% during follow-up, and the standardized change in non-specific bronchial hyperreactivity (NSBH) was -0.18.

In 18 studies, authors compared removal from exposure to continued exposure. Removal may increase the likelihood of reporting absence of asthma symptoms, with risk ratio (RR) 4.80 (95% confidence interval (CI) 1.67 to 13.86), and it may improve asthma symptoms, with RR 2.47 (95% CI 1.26 to 4.84), compared to continued exposure. Change in FEV1 % may be better with removal from exposure, with a mean difference (MD) of 4.23 % (95% CI 1.14 to 7.31) compared to continued exposure. NSBH may improve with removal from exposure, with standardized mean difference (SMD) 0.43 (95% CI 0.03 to 0.82).

In seven studies, authors compared reduction of exposure to continued exposure. Reduction of exposure may increase the likelihood of reporting absence of symptoms, with RR 2.65 (95% CI 1.24 to 5.68). There may be no considerable difference in FEV1 % between reduction and continued exposure, with MD 2.76 % (95% CI -1.53 to 7.04) . No studies reported or enabled calculation of change in NSBH.

In ten studies, authors compared removal from exposure to reduction of exposure. Following removal from exposure there may be no increase in the likelihood of reporting absence of symptoms, with RR 6.05 (95% CI 0.86 to 42.34), and improvement in symptoms, with RR 1.11 (95% CI 0.84 to 1.47), as well as no considerable change in FEV1 %, with MD 2.58 % (95% CI −3.02 to 8.17). However, with all three outcomes, there may be improved results for removal from exposure in the subset of patients exposed to low molecular weight agents. No studies reported or enabled calculation of change in NSBH.

In two studies, authors reported that the risk of unemployment after removal from exposure may increase compared with reduction of exposure, with RR 14.28 (95% CI 2.06 to 99.16). Four studies reported a decrease in income of 20% to 50% after removal from exposure.

The quality of the evidence is very low for all outcomes.

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