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Exposure to barnyard microbes lowered asthma, atopy risk in children

Ege MJ. N Engl Med. 2011;364:701-709.

Gern JE. N Engl J Med 2011; 364:769-770.

Children who are raised in farming environments are less likely to develop asthma and atopy, researchers have found.

Using two large cross-sectional studies to identify risk factors for childhood asthma and allergies, researchers compared the prevalence of asthma and atopy in children who lived on farms in rural areas of central Europe with children in a reference group. In the Prevention of Allergy Risk Factors for Sensitization in Children Related to Farming and Anthroposophic Lifestyle study (PARSIFAL; n=6,843) and the Multidisciplinary Study to Identify the Genetic and Environmental Causes of Asthma in the European Community (GABRIELA; n=9,668), mattress and house dust samples were evaluated for environmental bacteria not detectable by culture techniques and bacterial and fungal taxa.

Markus J. Ege, MD, and colleagues found that in both studies, children who lived on farms had lower incidence rates of asthma and atopy and were exposed to a larger variety of environmental microorganisms than those in the reference group. Researchers also found that diversity of microbial exposure was inversely related to the risk for asthma (PARSIFAL: OR=0.62; 95% CI, 0.44-0.89; GABRIELA: OR=0.86; 95% CI, 0.75-0.99). There was also an inverse relationship between incidence rates of asthma and circumscribed exposure to species in the fungal taxon eurotium (adjusted OR=0.37; 95% CI, 0.18-0.76) and to a variety of bacterial species, including Listeria monocytogenes, Bacillus, Corynebacterium and others (adjusted OR=0.57; 95% CI, 0.38-0.86).

“Identification of the association between exposure to an environment rich in nonpathogenic microbes and reduced risk of asthma offers hope that this and other new conceptual breakthroughs will lead to novel preventive strategies. These findings also raise additional questions about the possible mechanisms through which the nature and range of microbial exposure may alter the developmental biology of the lung and immune system,” James E. Gern, MD, of the departments of pediatrics and medicine at the University of Wisconsin School of Medicine and Public Health, wrote in an editorial accompanying the published study.

Disclosures: Drs. Ege and Gern report no relevant financial disclosures.

Ege et al present an intriguing argument for how childhood microbial exposure (through living on a farm) is associated with protection from developing asthma in Western European children. This study takes aim at the hygiene hypothesis and allergic disease development. The hygiene hypothesis proposes that exposure to microbes and infectious organisms in childhood primes the immune system in a Th1 direction which protects from allergy/atopy development, as opposed to a Th2 (allergy) direction. The concept has been a hot topic of debate for many years. This study, however, shows a fairly convincing association between farm living and high microbial exposure, and a lower rate of asthma. Furthermore, they were able to identify groupings of specific types of microorganisms associated with these findings in the study population, and noted that the diversity of the species recognition was inversely related to the development of asthma. These findings were consistent across two large, cross sectional groups taken at different time periods. Though exceptionally interesting, caution is warranted in interpreting these findings-asthma was defined as "physician diagnosed" on at least one occasion or wheezy bronchitis on more than one occasion, and may not represent the most robust criteria for diagnosing such a key outcome. With stricter and more objective criteria, their findings could have been vastly different. As well, it is unknown if these findings are specific for the particular geographic location where the studies were performed, or if these findings are particular to the European children used in both cross-sectional groups and would not generalize to children of other nationalities with similar farm exposures. However, in our clean modern-day society, where we protect our children from infection through methods ranging from an aggressive vaccination program to a seemingly omnipresent availability of instant hand sanitizer, one must wonder if our rising rates of allergy and atopic disorders parallel our efforts to reduce microbial exposure. Further study of this very interesting topic is certainly indicated. Hopefully such study will be able to provide further answers to the question about the balance of the immune system, and how factors like microbial organism exposure may influence this.

– Matthew J. Greenhawt, MD. MBA
Infectious Diseases in Children Editorial Board member

Disclosures: Dr. Greeenhawt reports no relevant financial disclosures.

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