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.

Results

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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Table 1. Frequency of reported farm animal contact in pregnancy and during first year of life in the various regions of the world where 6- to 7-year-old children were studied as part of the ISAAC Phase Three study
	Number of countries	Number of centres	N	Farm animal contact first year (%)	Farm animal contact pregnancy (%)
All centres	28	69	194 794	11.5	10.0
Africa	1	1	2304	25.6	23.5
Asia-Pacific	5	8	26 923	11.4	10.3
Eastern Mediterranean	3	5	15 012	15.5	14.9
Indian Sub-Continent	1	14	42 523	11.3	8.9
Latin America	6	16	43 388	11.1	9.8
North America	2	2	3921	8.6	7.7
Northern and Eastern Europe	5	6	15 115	12.0	12.4
Oceania	1	4	10 753	11.2	8.9
Western Europe	4	13	34 855	9.6	7.8

Table 2. Association between exposure to farm animals in the first year of life and symptoms of asthma, rhinoconjunctivitis and eczema in 6- to 7-year-old children
	OR (95% CI)
Outcome	Model 1^a (all children)	Model 2^b	Model 3^c
Current wheeze	1.27 (1.20–1.35)	1.14 (1.05–1.24)	1.09 (1.00–1.18)
Current symptoms of severe asthma	1.39 (1.29–1.50)	1.33 (1.19–1.49)	1.22 (1.09–1.37)
Asthma ever	1.14 (1.07–1.21)	1.01 (0.93–1.10)	0.98 (0.90–1.07)
Current symptoms of rhinoconjunctivitis	1.31 (1.24–1.40)	1.22 (1.12–1.34)	1.18 (1.08–1.30)
Current symptoms of severe rhinoconjunctivitis	1.43 (1.19–1.72)	1.42 (1.06–1.91)	1.21 (0.89–1.63)
Hay fever ever	1.18 (1.11–1.26)	1.12 (1.02–1.22)	1.10 (1.00–1.20)
Current symptoms of eczema	1.33 (1.25–1.41)	1.19 (1.10–1.30)	1.16 (1.07–1.27)
Current symptoms of severe eczema	1.89 (1.65–2.16)	1.48 (1.19–1.83)	1.31 (1.05–1.63)
Eczema ever	1.10 (1.04–1.17)	0.98 (0.91–1.06)	1.02 (0.94–1.10)

^aAdjusted for sex, region of the world, language and GNI per capita.
^bAdjusted for sex, region of the world, language and GNI. Including only centres with at least 70% data available for all covariates. All children who had a missing value for any of the covariates have been removed.
^cMultivariate analysis including centres with at least 70% data available for all covariates. All children who had a missing value for any of the covariates have been removed. Adjusted for sex, region of the world, language, GNI, cooking fuel, maternal education, current maternal and paternal smoking, exercise, television viewing, consumption of fast food, current paracetamol use, older and younger siblings and truck traffic in street of residence.

Table 3. Association between maternal exposure to farm animals during pregnancy and symptoms of asthma, rhinoconjunctivitis and eczema in 6- to 7-year-old children
	OR (95% CI)
Outcome	Model 1^a (all children)	Model 2^b	Model 3^c
Current wheeze	1.36 (1.28–1.44)	1.19 (1.09–1.30)	1.13 (1.03–1.24)
Current symptoms of severe asthma	1.47 (1.36–1.59)	1.36 (1.20–1.54)	1.23 (1.09–1.40)
Asthma ever	1.15 (1.08–1.22)	1.01 (0.92–1.10)	0.97 (0.88–1.06)
Current symptoms of rhinoconjunctivitis	1.33 (1.25–1.42)	1.29 (1.17–1.43)	1.24 (1.12–1.37)
Current symptoms of severe rhinoconjunctivitis	1.57 (1.30–1.90)	1.76 (1.30–2.37)	1.50 (1.11–2.03)
Hay fever ever	1.22 (1.14–1.30)	1.19 (1.08–1.31)	1.17 (1.06–1.29)
Current symptoms of eczema	1.30 (1.22–1.39)	1.21 (1.10–1.32)	1.17 (1.07–1.29)
Current symptoms of severe eczema	1.86 (1.61–2.16)	1.46 (1.15–1.85)	1.28 (1.00–1.62)
Eczema ever	1.06 (1.00–1.13)	0.98 (0.90–1.07)	1.01 (0.93–1.10)

Table 4. Associations between farm animal contact and current symptoms of asthma, rhinoconjunctivitis and eczema in 6-to-7-year-old children in affluent and non-affluent countries ^a
Region	Number of countries	Number of centres	n	OR^b (95% CI) asthma (wheeze)	OR^b (95% CI) rhinoconjunctivitis	OR^b (95% CI) eczema
Farm animal exposure in the first year of life
Affluent	6	19	41 782	0.96 (0.86–1.08)	1.06 (0.93–1.20)	0.95 (0.84–1.08)
Non-affluent	14	24	53 534	1.27 (1.12–1.44)	1.35 (1.18–1.55)	1.38 (1.23–1.55)
Farm animal exposure during pregnancy
Affluent	6	19	41 877	0.95 (0.84–1.08)	1.12 (0.98–1.29)	0.96 (0.84–1.11)
Non-affluent	14	24	53 558	1.38 (1.21–1.58)	1.38 (1.20–1.60)	1.37 (1.21–1.56)

Multiple regression analyses in children with complete covariate data.
^aWorld Bank classification for 2001.
^bMultivariate analysis including centres with at least 70% data available for all covariates. All children who had a missing value for any of the covariates have been removed. Adjusted for sex, region of the world, language, GNI per capita, cooking fuel, maternal education, current maternal and paternal smoking, exercise, television viewing, consumption of fast food, current paracetamol use, older and younger siblings and truck traffic in street of residence.

Table 5. Association between maternal and first-year exposure to farm animals and current symptoms of asthma, rhinoconjunctivitis and eczema in 6- to 7-year-old children in affluent and non-affluent countriesa
Outcome
	Pregnancy only OR^b (95% CI)			First year only OR^b (95% CI)			Pregnancy and first year OR^b (95% CI)
	Asthma (wheeze)	Rhinoconjunctivitis	Eczema	Asthma (wheeze)	Rhinoconjunctivitis	Eczema	Asthma (wheeze)	Rhinoconjunctivitis	Eczema
Affluent^c	1.14 (0.88–1.48)	1.44 (1.10–1.89)	1.37 (1.05–1.78)	1.08 (0.91–1.29)	1.10 (0.90–1.34)	1.11 (0.91–1.35)	0.91 (0.79–1.05)	1.05 (0.90–1.23)	0.87 (0.74–1.03)
Non-affluent^c	1.30 (1.04–1.62)	1.26 (0.98–1.61)	1.18 (0.96–1.47)	1.10 (0.90–1.33)	1.21 (0.98–1.50)	1.24 (1.05–1.48)	1.44 (1.23–1.68)	1.46 (1.23–1.73)	1.51 (1.31–1.76)

Multiple regression analyses in children with complete covariate data. The reference category for the ORs is no exposure to animals in pregnancy and in the first year at either time.
^aWorld Bank classification for 2001.
^bMultivariate analysis including centres with at least 70% data available for all covariates. All children who had a missing value for any of the covariates have been removed. Adjusted for sex, region of the world, language, gross national income per capita, cooking fuel, maternal education, current maternal and paternal smoking, exercise, television viewing, consumption of fast food, current paracetamol use, older and younger siblings and truck traffic in street of residence.
^cFrequency of exposure: pregnancy only 1.4% (affluent), 2.7% (non-affluent); first year only 3.2% (affluent), 4.3% (non-affluent); pregnancy and first year 5.5% (affluent), 6.3% (non-affluent).

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

An ISAAC Phase Three Study

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