Occupational Asthma Reference

Smit LAM, Heederik D, Doekes G, Blom C, van Zweden I, Wouters IM, Exposure–response analysis of allergy and respiratory symptoms in endotoxin-exposed adults, Eur Respir J, 2008;31:1241-1248,
(Plain text: Smit LAM, Heederik D, Doekes G, Blom C, van Zweden I, Wouters IM, Exposure-response analysis of allergy and respiratory symptoms in endotoxin-exposed adults, Eur Respir J)

Keywords: farmer, onion, seed merchant,bulb grower, endotoxin, hay fever, wheeze, air measurements, epidemiology, cross section, Holland

Known Authors

Dick Heederik, Institute of Risk Assessment Sciences, Utrecht Dick Heederik

Lidwien Smit, Utrecht University Lidwien Smit

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The objective of the present study was to investigate exposure–response relationships between current endotoxin exposure and allergic and respiratory symptoms in adults, taking into account farming exposures during childhood.

A cross-sectional study was conducted among 877 Dutch farmers and agricultural industry workers in 2006. Based on 249 full-shift personal airborne endotoxin samples, a job-exposure matrix was constructed to assign endotoxin exposure levels to all participants. Associations between endotoxin exposure and questionnaire data on symptoms were studied by multiple logistic regression.

Adjusted odds ratios (OR) for an interquartile range increase in endotoxin level were elevated for respiratory symptoms such as wheezing (OR 1.41 (95% confidence interval 1.16–1.72)), wheezing with shortness of breath (1.50 (1.18–1.90)) and daily cough (1.29 (1.03–1.62)). In contrast, endotoxin was strongly associated with a decreased prevalence of hay fever (0.62 (0.49–0.78)). Workers who had grown up on a farm had a lower prevalence of hay fever, but no evidence was found of effect modification by farm childhood.

In conclusion, occupational endotoxin exposure in adulthood is associated with an increased risk of asthma-like symptoms but a reduced prevalence of hay fever.

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The study found that current occupational exposure to endotoxin was associated with a reduced prevalence of hay fever in adults, regardless of childhood exposure. However, in the same population, a positive dose-dependent association between endotoxin exposure and adverse respiratory effects, such as wheezing, shortness of breath and cough, was found.

The possible confounding effects of biocides was eliminated by confining the farming population to organic farmers and controlling for childhood farm exposure.

The pro-inflammatory properties of endotoxin can explain the increased risk of airway symptoms such as wheezing and cough. Conversely, endotoxin is thought to reduce the risk of allergic sensitisation by inducing a shift from allergic T-helper cell (Th) type 2 responses to Th1-dominated responses, through stimulation of the innate immune system and regulatory T-cells. The results of the present study suggest that inhaled endotoxin may exert such immune-modulating effects beyond childhood, and similar conclusions were previously derived from a longitudinal study showing that young adult dairy farmers may lose allergic sensitisation over
time, especially to grass pollen.

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