Published Online: June 4, 2014
Half of children experience wheezing illnesses by the age of three, and in children who develop early allergic sensitization, or other signs of atopy during the preschool years, recurrent wheezing is a risk factor for asthma. The indoor environment of poor urban neighborhoods often exposes children to adverse conditions—including indoor pollutants and perennial allergens such as cockroaches and mice—which promote allergic sensitization and recurrent wheezing. Conversely, farm-related microbial exposures in early life have been linked to protection against allergic diseases. Notably, the effect of exposure to allergens and microbes on the risk of recurrent wheeze and allergic disease outcomes in urban settings is unknown.
In an article recently published in The Journal of Allergy and Clinical Immunology (JACI), Lynch and colleagues examined the relationship between exposure to specific allergens and microbes in the first year of life and recurrent wheeze and allergic sensitization at age three. They used data collected in the Urban Environment and Childhood Asthma study, a birth cohort study that is part of the Inner City Asthma Consortium sponsored by the National Institute of Allergy and Infectious Disease.
As expected, the authors found that cumulative allergen exposure over the first three years of life was associated with allergic sensitization, and that allergic sensitization was associated with recurrent wheeze. However, the major finding from the birth cohort study was that inner city children who were exposed in their first year of life to high levels of cockroach, mouse, or cat allergen in house dust were less likely to have a recurrent wheeze at age three. In addition, children with increased bacterial richness in their households, or who had increased exposure to certain specific bacteria, were less likely to develop atopy, with or without wheezing. Finally, combined analysis of exposure to both allergens and bacteria revealed that the group of children with neither wheeze nor atopy had the highest first year exposure to the specific allergens and the potentially protective bacteria.
The authors conclude that concomitant exposure to high levels of certain allergens and certain bacteria in early life may be beneficial, and that this information might be useful in identifying new preventive strategies for wheezing and allergic diseases.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.