Occupational asthma is the most frequently reported work-related respiratory disease in many countries. It is defined as asthma that is caused by a specific workplace exposure to certain substances and not to factors outside the workplace. In a recent review the population attributable risk for adult onset asthma being caused by occupational exposures was 17.6%. Occupational asthma can lead to decreased quality of life, sickness absence and increased costs for the patient, the employer and society. Early removal from exposure has been reported to be important in the prognosis of occupational asthma in a number of papers and reviews, but is not universally accepted as an important part of management.
Twenty-one articles were included in this review, reporting on 29 studies of three different interventions with 1447 participants. Fifteen studies compared workers that were removed from exposure to those who continued to be exposed. In another six studies, reduction of exposure was compared to continued exposure and in again another eight studies workers who were removed from exposure were compared to those for whom exposure was reduced. Outcomes were asthma symptoms and lung function at follow up. The overall quality of the studies was very low. Both removal from and reduction of exposure reduced asthma symptoms significantly but removal did better. Lung function improved significantly after removal but not after reduction of exposure. However, removal from exposure came at the cost of a much higher risk of unemployment and a greater decrease of income. Therefore, it remains uncertain how much better removal of exposure is compared to reduction of exposure and the benefit of symptom improvement should be balanced against the much higher risk of job loss and income decrease.
Further randomised controlled trials are needed to find out which interventions most effectively reduce the impact of occupational asthma.
There is very low-quality evidence that removal from exposure improves asthma symptoms and lung function compared with continued exposure.
Reducing exposure also improves symptoms, but seems not as effective as complete removal.
However, removal from exposure is associated with an increased risk of unemployment, whereas reduction of exposure is not. The clinical benefit of removal from exposure or exposure reduction should be balanced against the increased risk of unemployment. We need better studies to identify which interventions intended to reduce exposure give most benefit.
The impact of workplace interventions on the outcome of occupational asthma is not well-understood.
To evaluate the effectiveness of workplace interventions on the outcome of occupational asthma.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; NIOSHTIC-2; CISDOC and HSELINE up to February 2011.
Randomised controlled trials, controlled before and after studies and interrupted time series of workplace interventions for occupational asthma.
Two authors independently assessed study eligibility and trial quality, and extracted data.
We included 21 controlled before and after studies with 1447 participants that reported on 29 comparisons.
In 15 studies, removal from exposure was compared with continued exposure. Removal increased the likelihood of reporting absence of symptoms (risk ratio (RR) 21.42, 95% confidence interval (CI) 7.20 to 63.77), improved forced expiratory volume (FEV1 %) (mean difference (MD) 5.52 percentage points, 95% CI 2.99 to 8.06) and decreased non-specific bronchial hyper-reactivity (standardised mean difference (SMD) 0.67, 95% CI 0.13 to 1.21).
In six studies, reduction of exposure was compared with continued exposure. Reduction increased the likelihood of reporting absence of symptoms (RR 5.35, 95% CI 1.40 to 20.48) but did not affect FEV1 % (MD 1.18 percentage points, 95% CI -2.96 to 5.32).
In eight studies, removal from exposure was compared with reduction of exposure. Removal increased the likelihood of reporting absence of symptoms (RR 39.16, 95% CI 7.21 to 212.83) but did not affect FEV1 % (MD 1.16 percentage points, 95% CI -7.51 to 9.84).
Two studies reported that the risk of unemployment after removal from exposure was increased compared with reduction of exposure (RR 14.3, 95% CI 2.06 to 99.16). Three studies reported loss of income of about 25% after removal from exposure.
Overall the quality of the evidence was very low.