Children who grow up in environments that afford them a wide range of microbial exposures,
such as traditional farms, are protected from childhood asthma and atopy. In previous
studies, markers of microbial exposure have been inversely related to these conditions.
In two cross-sectional studies, we compared children living on farms with those in
a reference group with respect to the prevalence of asthma and atopy and to the diversity
of microbial exposure. In one study--PARSIFAL (Prevention of Allergy-Risk Factors
for Sensitization in Children Related to Farming and Anthroposophic Lifestyle)--samples
of mattress dust were screened for bacterial DNA with the use of single-strand conformation
polymorphism (SSCP) analyses to detect environmental bacteria that cannot be measured
by means of culture techniques. In the other study--GABRIELA (Multidisciplinary Study
to Identify the Genetic and Environmental Causes of Asthma in the European Community
[GABRIEL] Advanced Study)--samples of settled dust from children's rooms were evaluated
for bacterial and fungal taxa with the use of culture techniques.
In both studies, children who lived on farms had lower prevalences of asthma and atopy
and were exposed to a greater variety of environmental microorganisms than the children
in the reference group. In turn, diversity of microbial exposure was inversely related
to the risk of asthma (odds ratio for PARSIFAL, 0.62; 95% confidence interval [CI],
0.44 to 0.89; odds ratio for GABRIELA, 0.86; 95% CI, 0.75 to 0.99). In addition, the
presence of certain more circumscribed exposures was also inversely related to the
risk of asthma; this included exposure to species in the fungal taxon eurotium (adjusted
odds ratio, 0.37; 95% CI, 0.18 to 0.76) and to a variety of bacterial species, including
Listeria monocytogenes, bacillus species, corynebacterium species, and others (adjusted
odds ratio, 0.57; 95% CI, 0.38 to 0.86).
Children living on farms were exposed to a wider range of microbes than were children
in the reference group, and this exposure explains a substantial fraction of the inverse
relation between asthma and growing up on a farm. (Funded by the Deutsche Forschungsgemeinschaft
and the European Commission.).