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Occup Environ Med. 2013 Sep;70(9):603-10. doi: 10.1136/oemed-2013-101362. Epub 2013 Jun 12.

Work related asthma. A causal analysis controlling the healthy worker effect.

Author information

1
Inserm, Center for research in Epidemiology and Population Heatlh (CESP), U1018, Respiratory and Environmental Epidemiology team, F-94807, Villejuif, France. orianne.dumas@inserm.fr

Abstract

OBJECTIVES:

The healthy worker effect usually leads to underestimation of the association between occupational exposure and asthma. The role of irritants in work-related asthma is disputed. We estimated the effect of occupational exposure on asthma expression in a longitudinal study, using marginal structural modelling to control for the healthy worker effect.

METHODS:

Analyses included 1284 participants (17-79 years, 48% men) from the follow-up (2003-2007) of the French Epidemiological study on the Genetics and Environment of Asthma (case-control study). Age at asthma onset, periods with/without attacks over lifetime and occupational history were recorded retrospectively. Exposures to known asthmagens, irritants or low level of chemicals/allergens were evaluated through a job-exposure matrix. The job history was reconstructed into 5-year intervals.

RESULTS:

Thirty-one per cent of subjects had ever been exposed to occupational asthmagens. Among the 38% of subjects who had asthma (ever), presence of attacks was reported in 52% of all time periods. Using standard analyses, no association was observed between exposure to known asthmagens (OR (95% CI): 0.99 (0.72 to 1.36)) or to irritants/low level of chemicals/allergens (0.82 (0.56 to 1.20)) and asthma attacks. Using a marginal structural model, all associations increased with suggestive evidence for known asthmagens (1.26 (0.90 to 1.76)), and reaching statistical significance for irritants/low level of chemicals/allergens (1.56 (1.02 to 2.40)).

CONCLUSIONS:

The healthy worker effect has an important impact in risk assessment in work-related asthma studies. Marginal structural models are useful to eliminate imbalances in exposure due to disease-driven selection. Results support the role of irritants in work-related asthma.

PMID:
23759534
DOI:
10.1136/oemed-2013-101362
[Indexed for MEDLINE]
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