Epidemiology and Diagnosis of Virus-Induced Asthma Exacerbations
Attacks of asthma are a major cause of respiratory morbidity and mortality worldwide. Most asthma attacks do not ﬁt the characteristic features of inhaled allergen response: rapid onset within 30 min of exposure to an allergen, and a biphasic response, recovering within 24 h. Upper respiratory signs, particularly nasal symptoms, precede many attacks with a latency of 24-48 h, and many asthma attacks involve symptoms lasting several days to a week, and deterioration in lung function that may last 2 weeks (1-3). Whereas day-to-day asthma symptoms precipitated by allergens, exercise, or cold air are brought readily under control with inhaled steroids, asthma attacks are often not as easily prevented (4). These observations of common clinical experience indicate that there are reasons for asthma attacks other than allergen exposure or dehydration of the airway epithelium secondary to exercise or dry air inhalation.