Objective To test the hypotheses that current endotoxin exposure is inversely associated with allergic sensitisation and positively associated with non-allergic respiratory diseases in four occupationally exposed populations using a standardised analytical approach.
Methods Data were pooled from four epidemiological studies including 3883 Dutch and Danish employees in veterinary medicine, agriculture and power plants using biofuel. Endotoxin exposure was estimated by quantitative job-exposure matrices specific for the study populations. Dose–response relationships between exposure, IgE-mediated sensitisation to common allergens and self-reported health symptoms were assessed using logistic regression and generalised additive modelling. Adjustments were made for study, age, sex, atopic predisposition, smoking habit and farm childhood. Heterogeneity was assessed by analysis stratified by study.
Results Current endotoxin exposure was dose-dependently associated with a reduced prevalence of allergic sensitisation (ORs of 0.92, 0.81 and 0.66 for low mediate, high mediate and high exposure) and hay fever (ORs of 1.16, 0.81 and 0.58). Endotoxin exposure was a risk factor for organic dust toxic syndrome, and levels above 100 EU/m3 significantly increased the risk of chronic bronchitis (p<0.0001). Stratification by farm childhood showed no effect modification except for allergic sensitisation. Only among workers without a farm childhood, endotoxin exposure was inversely associated with allergic sensitisation. Heterogeneity was primarily present for biofuel workers.
Conclusions Occupational endotoxin exposure has a protective effect on allergic sensitisation and hay fever but increases the risk for organic dust toxic syndrome and chronic bronchitis. Endotoxin's protective effects are most clearly observed among agricultural workers.
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Funding The GABRIEL project (http://www.gabriel-fp6.org) is funded by a contract from the European Commission (018996) and grants from the French Ministry of Research, the Wellcome Trust (WT084703MA) and Asthma UK. The SUS study has received contributions from The Danish Agency for Science Technology and Innovation, The Danish Medical Research Council, The Danish Agricultural Research Council, Helsefonden, and the PC Petersen Foundation, whereas its ongoing part is funded by the Danish Working Environment Research Fund, The Danish Research Council Aarhus University and The Danish Lung Association. The Danish biofuel workers study was funded by the PSO-ELTRA (grant numbers 4774 and 4785) Energitilsynet, Nyropsgade 30, 1780 Copenhagen V. The Dutch study on farmers and agricultural workers was funded by the Netherlands Asthma Foundation (Grant No. 3.2.03.70) and The Veterinarians Health study by Utrecht University.
Competing interests None.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the Ethics Committee for Aarhus County and the institutional ethics committee of the University of Utrecht (University Medical Center Utrecht, The Netherlands) for the participating Danish and Dutch studies, respectively.
Provenance and peer review Not commissioned; externally peer reviewed.
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