Lierl MB, Hornung RW. Ann Allergy Asthma Immunol. 2003;90:28–33
Purpose of the Study.
To determine the relationship of outdoor air quality parameters to asthma exacerbations among children.
Pediatric patients who had experienced an emergency department visit or an inpatient hospitalization at Cincinnati Children’s Hospital for treatment of acute asthma were studied.
The number of emergency department visits and hospitalizations for treatment of asthma were determined by review of emergency department logs and a hospital computer database. Air quality data were obtained from a centrally located monitoring station. Ozone concentrations were continuously monitored, and data were recorded as daily averages and the highest 1-hour average concentration for each day. Concentrations of airborne particulates <10 μm in diameter were obtained by using a volumetric air sampler with a size-selective inlet, and 24-hour average values were calculated. Pollen and fungal counts were obtained by using a Rotorod sampler (Multidata, Inc, Plymouth Meeting, PA). Multiple-regression models were developed to examine all potential exposure measures as predictors of the number of daily asthma visits. Poisson regression analysis was used to model the daily number of asthma visits as a function of air quality data and temporal variables. In the data analyses, air quality measures from 0 to 5 days before the asthma visit date were used, to account for delayed effects.
A series of Poisson regression models was used to identify predictors of changes in the number of asthma visits. Initially, the logarithm of pollen counts and the month of the year (April to October) were significant predictors of the number of asthma visits. The number of asthma visits per day was associated with pollen counts reported for the same day (P = .014). The effect was increasingly strong, however, for pollen counts recorded 1, 2, and 3 days before the visit. The logarithm of the pollen counts lagged 3 days was the most significant predictor of asthma visits (P < .001). This effect was very strong during the summer and spring months; however, in the autumn, when pollen counts and asthma visits were both high, daily variations in pollen counts did not account for the variations in daily asthma visits as they did during other seasons. The analyses also showed a synergistic effect between pollen and particulate levels, in that the exposure-response to pollen counts was moderately high on days when particulate matter levels were low but was significantly higher on days when particulate matter levels were >33 μg/m3. Fungal spore counts and average ozone concentrations were not significant predictors of asthma visits.
Ambient concentrations of pollens and small particles were strongly associated with emergency visits for treatment of pediatric asthma in Cincinnati, Ohio. Concentrations of ozone did not appear to be associated with pediatric asthma exacerbations.
Several studies have demonstrated associations between particulate matter levels and emergency department visits, and several have shown correlations between pollen counts and asthma symptoms. This study shows the added effects of both on asthma symptoms. It would be interesting to evaluate particulate matter levels and pollen counts in various urban, suburban, and rural settings, to assess their influence. In addition, examination of particulate matter levels inside and outside households, schools, and offices might give us a better understanding of the conditions that influence asthma. The fact that pollen counts influenced asthma admissions in the spring and summer but not the autumn might be secondary to other factors that dominate during that season (eg, cold weather and respiratory infections).