Occupational Asthma Reference

de Groene GJ, Pal TM, Beach J, Tarlo SM, Spreeuwers D, Frings-Dresen MH, Mattioli S, Verbeek JH, Workplace interventions for treatment of occupational asthma, Cochrane Database of Systematic Reviews, 2011;5:1-93,

Keywords: Cochrane, evidence-based review, prognosis, exposure reduction, unemployment

Known Authors

Jeremy Beach, University of Alberta Jeremy Beach

Susan Tarlo, Toronto Susan Tarlo

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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 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.

Cochrane Database of Systematic Reviews 2011, Issue 5. Art. No.: CD006308. DOI: 10.1002/14651858.CD006308.pub3

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Comments

The authors grade the quality of evidence as very low using Cochrane methodology, and make the following recomendations for future research into outcomes of occupational asthma including randomisation of workers into removal from exposure or exposure reductionable. It would need a very special employment situation to be able to do this.
" Future studies should include greater numbers of participants and collect better information on exposure,duration of symptoms before diagnosis, duration of symptoms before the intervention and report more fully on asthma
symptoms, FEV1 and NSBH before, during and after the intervention. Studies are needed to fully evaluate the effect of reduction of exposure, through either personal protective equipment or education of workers after exposure is minimised, as far as reasonably achievable. Given the uncertainty of the effect of reduction of exposure and the beneficial effects of continued employment on health, these studies should randomise participants to reduction of exposure or removal from exposure"

Using the Bradford Hill Criteria for casation from epidemiological studies the data stacks up strongly. The strength of the asssociation between exposure removal and reduction is high, it is biologically plausable, repeated in many different populations, has "dose-response" (earlier removal better and exposure reduction worse). It has temporal plausability.
7/1/2012

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