ABSTRACT
Viral respiratory tract infections are the major cause of asthma exacerbations in children and adults. Up to 85% of asthma exacerbations in children1 and 44% in adults2 are associated with viral upper respiratory tract infections. These observations suggest that respiratory viruses are a major factor in provoking existing asthma and may accomplish this by enhancing existing airway inflammation. Furthermore, there is evidence that respiratory tract infections cause frequent episodes of wheezing in infants and may even be a factor in causing expression of asthma. Thus, respiratory infections can have two major effects on asthma: (1) a ‘possible’ etiological role in initiating asthma in infants and (2) the major cause of asthma exacerbations in patients who already have the disease. The evidence for a role of bacterial respiratory infection in either the initiation or promotion of asthma is not as well understood or established as in the case of viral respiratory infections. In this chapter, we will focus mainly on the role and contribution of viral respiratory infections
asthma, the interactions between respiratory viruses and other risk factors for asthma, and the possible mechanisms of virus-induced asthma exacerbations.
