Abstract and Introduction
Background Associations between early life exposure to farm animals and respiratory symptoms and allergy in children have been reported in developed countries, but little is known about such associations in developing countries.
Objective To study the association between early life exposure to farm animals and symptoms of asthma, rhinoconjunctivitis and eczema in a worldwide study.
Methods Phase Three of the International Study of Asthma and Allergies in Childhood (ISAAC) was carried out in 6- to 7-year-old children in urban populations across the world. Questions about early life exposure to farm animals (at least once/week) were included in an additional questionnaire. The association between such exposures and symptoms of asthma, rhinoconjunctivitis and eczema was investigated with logistic regression. Adjustments were made for gender, region of the world, language, gross national income and 10 other subject-specific covariates.
Results A positive association was found between early exposure to farm animals and the prevalence of symptoms of asthma, rhinoconjunctivitis and eczema, especially in non-affluent countries. In these countries, odds ratios (ORs) for 'current wheeze', 'farm animal exposure in the first year of life' and 'farm animal exposure in pregnancy' were 1.27 [95% confidence interval (CI) 1.12–1.44] and 1.38 (95% CI 1.21–1.58), respectively. The corresponding ORs for affluent countries were 0.96 (95% CI 0.86–1.08) and 0.95 (95% CI 0.84–1.08), respectively.
Conclusion Exposure to farm animals during pregnancy and in the first year of life was associated with increased symptoms of asthma, rhinoconjunctivitis and eczema in 6- to 7-year-old children living in non-affluent but not in affluent countries.
Studies in farming communities have shown that children in these communities have less allergic disease; several factors could explain this protective effect, including exposure to farm animals during pregnancy of the mother and/or in early life as discussed in a recent review based on studies which were mostly conducted in Europe and North America.
The large majority of studies on farm animal exposure have been conducted in affluent countries, and it is not clear to what extent the findings can be extrapolated to child populations living in other parts of the world. A small number of studies have addressed the relationship between farm animal exposure and childhood allergic symptoms in non-Western populations, and, interestingly, these have in some cases found positive relationships between various measures of farm animal exposure (including exposure to farm animals in pregnancy) and childhood symptoms. As an example, one of the International Study of Asthma and Allergies in Childhood (ISAAC) Phase Three centres in Mexico reported a positive association between cumulative asthma in 6- to 7-year-old children and exposure of the mother to farm animals in pregnancy in boys [odds ratio (OR) 1.86, 95% confidence interval (CI) 1.14–3.03] as well as girls (OR 1.73, 95% CI 0.92–3.26).
In this article, we present findings on farm animal exposure from Phase Three of ISAAC, which was a questionnaire-based assessment conducted in a total of 1 187 495 children from 238 centres located in 98 countries in all parts of the world. The analyses in this article are restricted to 194 794 6- to 7-year-old children for whom data on exposure to farm animals were collected.
Int J Epidemiol. 2012;41(3):753-761. © 2012 Oxford University Press
Copyright 2007 International Epidemiological Association. Published by Oxford University Press. All rights reserved.