A new study confirms the pattern of fall/winter worsening of asthma symptoms and related medical visits and summer improvement. Surprisingly, seasonal variation in environmental allergens is not the source of this difference. A more likely cause could be increased viral respiratory infections during fall and winter months, according to Peter J. Gergen, M.D., M.P.H., formerly of the Agency for Healthcare Research and Quality and now with the National Institute on Allergy and Infectious Diseases. Dr. Gergen and his colleagues tracked children ages 4 to 12 who were participating in the National Cooperative Inner-City Asthma Study (NCICAS) for about 4 years after allergen skin testing and determination of exposure to environmental tobacco smoke. They also obtained air pollution data from EPA monitoring sites in the NCICAS cities.
Analysis of the data on 1,641 children revealed that all three measures of asthma-related illness (wheeze, unscheduled medical visits, and hospitalizations) started to peak in September and reached their highest levels in winter. These same measures reached their lowest levels in the summer months of June through August. Seasonal patterns were similar among children with no allergen skin test reactivity; those reactive only to indoor allergens such as dust mites, cockroaches, and animal dander; and those who were reactive to outdoor allergens such as trees or ragweed.
The mean days of wheeze averaged over the full time period were similar for the three groups: no skin test reactivity, 6.9 days/month; indoor reactors, 7.3 days/month; and outdoor reactors, 7.1 days/month. Environmental tobacco smoke was not related to observed seasonal patterns. Among four air pollutants evaluated (sulphur dioxide, nitrogen dioxide, particulates, and ozone), only sulfur dioxide coincided with worsening of asthma symptoms, but its impact on those symptoms was questionable. The increase of indoor allergen exposure in fall and winter may not be enough to influence the activity of the disease, suggest the researchers. The yearly cycle of asthma attacks may be driven primarily by viral infections. Future vaccines against these infections may reduce these seasonal fluctuations.
See "Understanding the seasonal pattern of childhood asthma: Results from the National Cooperative Inner-City Asthma Study (NCICAS)," by Dr. Gergen, Herman Mitchell, Ph.D., and Henry Lynn, Ph.D., in the November 2002 Journal of Pediatrics 141, pp. 631-636.
Reprints (AHRQ Publication No. 03-R017) are available from the AHRQ Publications Clearinghouse.
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