Inverse association between farm animal contact and respiratory allergies in adulthood: protection, underreporting or selection?

Authors

  • K. Radon,

    1. Unit for Occupational and Environmental Epidemiology and Net Teaching, Institute for Occupational and Environmental Medicine, Ludwig-Maximilians-University, Munich, Germany
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  • A. Schulze,

    1. Unit for Occupational and Environmental Epidemiology and Net Teaching, Institute for Occupational and Environmental Medicine, Ludwig-Maximilians-University, Munich, Germany
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  • D. Nowak

    1. Unit for Occupational and Environmental Epidemiology and Net Teaching, Institute for Occupational and Environmental Medicine, Ludwig-Maximilians-University, Munich, Germany
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Katja Radon
Unit for Occupational and Environmental Epidemiology and Net Teaching
Institute for Occupational and Environmental Medicine
Ziemssenstr. 1
80336 Munich
Germany

Abstract

Background:  It has been argued that the inverse association between exposure to farm animals and nasal allergies observed in children and adults might be because of self-selection.

Aims:  We aimed to assess the health-based selection out of farming in adults.

Material and methods:  A cross-sectional study was carried out in a rural region. Overall, 4053 inhabitants (63%) aged 18–44 years responded to a questionnaire on respiratory diseases, life-time exposure to farming environments and potential confounders. For 2678 of these, specific immunoglobulin E to common allergens was available. The outcome was: (i) sensitization and symptoms of nasal allergies (symptomatic sensitization); (ii) sensitization without symptoms of nasal allergies (asymptomatic sensitization).

Results:  Farm animal contact in childhood was associated with a decreased risk of symptomatic and asymptomatic sensitization. Continued exposure to farm animals in adulthood further decreased the odds ratio of symptomatic (odds ratio 0.2; 95% confidence interval 0.1, 0.4) but not asymptomatic sensitization (0.7; 0.4, 1.1). Starting farm animal contact in adulthood even increased the odds ratio of asymptomatic sensitization (2.4; 1.1, 5.2).

Conclusions:  The preventive effect of childhood contact to farm animals against sensitization continues into adulthood. However, in adulthood self-selection based on symptoms and underreporting of symptoms might also play a role.

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