Parental farming protects children against atopy: longitudinal evidence involving skin prick tests.

Abstract

There is growing evidence that the development of allergic sensitization can be influenced by environmental co-factors. Studies showed that growing up on a farm can protect children against allergic sensitization. However, little is known whether this 'farming effect' can only be observed in early lifetime or whether it also plays a role in later childhood. The aim of our study was to test whether a farming environment is negatively associated with a new occurrence of skin prick test (SPT) positivity in school children. As a secondary outcome we investigated whether children living on a farm lose their allergic sensitization more frequently than other children. In a longitudinal design, 1150 elementary school children (mean age 7.8 years, SD 0.7) were recruited from nine different areas of Austria in 1994. A questionnaire and an SPT involving seven common aero-allergens were performed at study entry and at follow-up 3 years later. A total of 844 children, who underwent two SPTs, were included in the analyses; 15.1% of their families reported working on a farm. Adjusting for potential confounders (parental education, number of siblings, sex, family history of allergy), parental farming was inversely related to the prevalence and new occurrence of SPT positivity [no farming 12.2%, part-time farming 6%, full-time farming 2.2% incidence; odds ratio (OR) farming vs. non-farming 0.34, 95% confidence interval (CI) 0.12-0.98]. Furthermore, children living in a farming environment were more likely to lose their SPT positivity during follow-up (no farming 14.6%, part-time farming 50%, full-time farming 60% loss of sensitization; OR farming vs. non-farming 8.06; 95% CI 2.05-31.75). No difference in the pattern of sensitization to specific allergens could be observed between farming and non-farming children. A farming environment has a strong negative effect on the development of allergic sensitization. Furthermore, the study provides evidence that atopic children living on a farm lose their SPT positivity more frequently than children from non-farming environments.