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 the outcome of occupational asthma.
Search strategy: We searched the Cochrane Central Register of Controlled Trials (CENTRAL); MEDLINE; EMBASE; NIOSHTIC-2; CISDOC and HSELINE up to February 2011.
Selection criteria: Randomised 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 trial quality, and extracted data.
Main results: 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.
Authors' conclusions: 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.