The Benefits of Broader Exposure
By Carol A. Kemper, MD, FACP, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases. Dr. Kemper does research for Abbott Laboratories and Merck. This article originally appeared in the April issue of Infectious Disease Alert. At that time it was peer reviewed by Timothy Jenkins, MD, Assistant Professor of Medicine, University of Colorado, Denver Health Medical Center. Dr. Jenkins reports no financial relationship to this field of study.
Source: Ege MJ, et al. Exposure to environmental microorganisms and childhood asthma. N Engl J Med 2011;364:701-709.
It has been speculated that children growing up in an overly clean, suburban environment may experience greater atopy and asthma than children growing up in the inner city or on a farm. These investigators report on the results obtained from two large-scale cross-sectional studies, performed in Europe, comparing the prevalence of atopy and asthma in children. The first study focused on 6963 children of farmers and school-aged children (ages 6-13 years) growing up in largely rural areas of central Europe; 52% lived on a farm; and 8% had a diagnosis of asthma. Dust from the children's mattresses were collected and DNA extractions were performed. The second study focused on a stratified random sample of 3668 school-aged children (ages 6-12 years) living in central Europe. Only 16% of these children lived on farms and 11% of these children had a diagnosis of asthma. Airborne dust samples were collected from the children's bedrooms for 2 weeks.
Both studies revealed that the risk of asthma was inversely related to the diversity of microbial exposure in the children's bedroom environment, independent of whether they lived on a farm. In addition, the presence of a more circumscribed range of exposure to a few organisms was also inversely related to an increased risk of asthma. Attempts to create a statistically relevant diversity score, either by a factor analysis or by summing the total exposure, demonstrated that diversity of flora, however it was measured, was significantly less in children with asthma (but not atopy).
Several "zones" identified in the factor analysis suggested that exposure to groups of bacteria and fungi were associated with a protective effect, although no single organism could be identified as protective. In addition, exposure to fungal taxon eurotium and penicillium seemed to have a protective effect.