Viral Infections and Associated Factors That Promote Acute Exacerbations of Asthma

Kim, Chang-Keun; Callaway, Zak; Gern, James E.

Asthma exacerbation is defined as an acute or subacute worsening of symptoms and lung function as compared to the patient's usual health status or, occasionally, the initial presentation of asthma. 6 Exacerbations often represent essentially an exaggerated lower airway response to an environmental exposure, with airway inflammation being a key component that promotes airflow obstruction and increased airway hyperresponsiveness. 7 Early treatment of asthma exacerbation is con-sidered the best strategy for management, 8 and increases in eosinophilic inflammatory markers have been shown to be good predictors of asthma exacerbations. 9 Utilizing this idea, tailoring patient treatment based on the direct and objective measurement of the eosinophil, a key component of airway inflammation in asthma, has proven more efficacious (e.g., less frequent and severe asthma exacerbations) than treatment based on clinical symptoms and lung function. 10 Exacerbations usually occur in response to a variety of external agents (e.g., respiratory pathogens, allergens, air pollutants, smoke, and cold or dry air); however, it is estimated that up to 85% of asthma exacerbations in children 11 and a considerable proportion in adults (76%-80%) 12 are linked to viral infections. The severity of the situation is compounded by the lack of specific antiviral strategies. Virus-induced asthma exacerbations are most often associated with detection of RV, 5 RSV, 13 human parainfluenza virus (HPIV), 14 human influenza virus (HIFV), 15 and human adenovirus (HAdV). 16 More recently, human bocavirus (HBoV), HMPV, 17 certain strains of human coronavirus (HCoV) (e.g., HCoV-NL63, HCoV-OC43, and HCoV-229E), 18 and EV-D68 19 have been associated with asthma exacerbation.