Of the chronic diseases affecting grade school children, asthma is the most common and accounts for the greatest number of school days missed. Moreover, it can influence family dynamics and function in other ways and, unfortunately, it may also be associated with mortality, particularly in the inner city environments of the United States. Thus, understanding factors that lead to its development in early life is essential in developing strategies aimed at primary prevention. Two risk factors that have been identified by a number of investigators include first, the development of allergic sensitization and second, wheezing respiratory tract illnesses caused by viruses and bacteria, either alone or in combination. Both of these factors appear to exert their influences within the first few years of life such that asthma becomes established prior to the child entering grade school at age 5 to 6 years. Since both allergic sensitization and viral and bacterial illnesses can occur in children who do not develop asthma, it is therefore paramount to identify genetic and environmental factors that activate, interact, and/or direct the immune system and components of the respiratory tract along pathways that allow asthma to become established and expressed clinically.
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