Early Life Exposure to Farm Animals and Symptoms of Asthma, Rhinoconjunctivitis and Eczema

An ISAAC Phase Three Study

Bert Brunekreef; Erika Von Mutius; Gary K Wong; Joseph A Odhiambo; Tadd O Clayton


Int J Epidemiol. 2012;41(3):753-761. 

In This Article


Data from 6- to 7-year-old children from 69 centres in 28 countries are included in the analyses of farm animal exposures. The analysis of exposure to farm animals in the first year includes 194 794 children and the analysis of maternal exposure to farm animals during pregnancy includes 194 598 children. Table 1 shows the range of reported percentages of farm animal exposure by area of the world. The highest farm animal exposure was found in the one participating centre from Africa; the lowest in North America. The average percentage of children in all centres whose mothers had been exposed to farm animals in pregnancy (10%) and of children exposed to farm animals in the first year of life (11.5%) shows that these exposures were relatively uncommon in the ISAAC Phase Three populations.

Table 2 shows the associations between farm animal exposure in the first year of life and symptoms. There was a positive association with most symptoms (especially severe symptoms of asthma and eczema) after adjustment for all covariates. Similar findings were obtained in the analysis of farm animal exposure during pregnancy of the mothers of the index children ( Table 3 ). Additional adjustment for cat and dog exposure in the first year of life made virtually no difference to these associations (results not shown). As these tables show, the largest differences in ORs were generally found when centres were excluded that had insufficient data on covariates.

When the analyses were stratified by country affluence, it became clear that most of the associations were much stronger in the non-affluent than in the affluent countries ( Table 4 ). In fact, most ORs in the affluent countries became close to unity, indicating no effect. Results were generally similar for boys and girls (results not shown).

Table 5 shows the results of an analysis in which children with farm animal exposure in pregnancy only, during the first year of life only, and during both periods are compared with children without farm animal exposure in either period. The frequencies of exposure mentioned in the footnote to Table 5 show that exposure during pregnancy and in the first year was most frequent (5.5% in affluent countries, 6.3% in non-affluent countries), but considerable frequencies were also found in categories of exposure during pregnancy only or during the first year only (4.6% affluent, 7.0% non-affluent). The strongest positive associations were found in children in non-affluent countries with exposure to farm animals during both periods. In affluent countries, symptoms of rhinoconjunctivitis and eczema were positively associated with exposure in pregnancy only, which was reported for only 1.4% of the children in this group of countries. The strongest associations were found in the non-affluent countries. Adjustment for cat and dog exposure in the first year of life again did not change the findings (results not shown).


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