Occupational endotoxin exposure dose-dependently protects against atopy and hay fever: Results of a longitudinal study

Background: Cross-sectional studies have shown a protective effect of farming and endotoxin exposure on allergic responses. As yet, longitudinal evidence of a protective exposure-response relationship is limited.Objective: To study dose response relationships between occupational endotoxin exposure and changes in respiratory health and atopic sensitization in adults.Methods: Health data were available for 234 farmers and agricultural workers both at baseline and 5 years later. Endotoxin exposure was modelled using a job exposure matrix. Respiratory symptoms were assessed by questionnaire, specific and total serum IgE levels by ELISA and lung function by spirometry. Associations between exposure and changes in health outcomes during follow-up were determined by logistic regression.Results: A twofold increase in personal endotoxin exposure was associated with increased loss of hay fever symptoms (OR 2.19 95%CI [0.96-4.99]), less persistent hay fever (OR 0.68 [0.54-0.87]), and a non-significant tendency for less new-onset of hay fever (OR 0.87 [0.65-1.17]). Similar patterns were observed for grass IgE positivity and atopic sensitization (ORs loss: 1.24 and 1.03; p>0.2, ORs persistent: 0.81[0.68 -0.97] and 0.89 [0.77-1.03], ORs new-onset: 0.83 [0.61-1.12] and 0.75 [0.55-1.02], respectively). Results are indicative of a consistent protective pattern, irrespective of farm childhood. Endotoxin exposure was not associated with changes in lung function.Conclusions: We showed a longitudinal protective effect of occupational endotoxin exposure for hay fever, atopy and grass IgE positivity.