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The Similarities and Differences of Epidemic Cycles of Chronic Obstructive Pulmonary Disease and Asthma Exacerbations

¹ Firestone Institute for Respiratory Health, Hamilton, Ontario, Canada

Correspondence and requests for reprints should be addressed to Neil W. Johnston, M.Sc., St. Joseph's Healthcare, 50 Charlton Avenue, East Hamilton, ON, Canada L8N 4A6. E-mail: njohnsto{at}sympatico.ca

ABSTRACT

The majority of chronic obstructive pulmonary disease (COPD) and asthma exacerbations in both children and adults are associated with respiratory viral infections and are cyclic in nature. Some variation in these cycles is associated with the timing of the appearance of respiratory viruses, particularly influenza and respiratory syncytial virus. Much more, however, is associated with signal events that are of either fixed or predictable timing. In children, asthma exacerbations reach epidemic levels following school return after the summer vacation and these are predominantly associated with rhinovirus infections. Although younger adults experience a rise in asthma exacerbations at this time, these are secondary to the epidemic in children. Older adults with either COPD or asthma experience only a slightly elevated risk of exacerbations after school return, and hospital presentations for pneumonia in any age group show only marginal increases at that time. Exacerbations of both COPD and adult asthma, with increasing risk with age, are at their highest average annual levels during the Christmas period. This effect appears to be independent of the timing of above average levels of influenza, RSV, parainfluenza, or adenovirus detections; however, hospitalization for respiratory tract infections in all age groups reaches high levels at the same time. Both the post–summer vacation asthma epidemic and the Christmas epidemic of COPD, asthma, and pneumonia are synchronous with the timing of signal events, the day of school return for the former and Christmas Day for the latter, and have been for several years. The agents responsible for the Christmas epidemic of respiratory diseases have not yet been identified. The differences between age and disease exacerbation patterns after school return and at Christmas suggest that either different agents are involved or that the response to a common agent is different between the two signal events.

Key Words: COPD • asthma • exacerbations • epidemiology