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Asthma is one of the most common chronic diseases among school-aged children in the United States. Environmental respiratory irritants exacerbate asthma among children. Understanding the impact of a variety of known and biologically plausible environmental irritants and triggers among children in New Jersey - ozone, PM2.5, tree pollen, weed pollen, grass pollen and ragweed- will allow informed public health interventions.
METHODS:
Time-stratified case-crossover design was used to study the transient impact of ozone, PM2.5 and pollen on the acute onset of pediatric asthma. Daily asthma visits were obtained for children aged 3-17 years with a primary diagnosis of asthma during the warm season (April through September), for 2004-2007. Bi-directional control sampling was used to select two control periods for each case visit day for a total of 65,562 inclusion days. Since the period of exposure prior to emergency department visit is most clinically relevant, lag exposures will be investigated (lag0, 1, 2, 3, 4, and 5 as well as 3-day and 5-day moving averages). Multivariable conditional logistic regression controlling for holiday, day of week, school-in-session indicator, and 3-day moving average for temperature and relative humidity was used to examine the associations. Risk ratios are based on interquartile range (IQR) increases or 10 unit increases when IQR ranges were narrow. Single-pollutant models for each exposure as well as multipollutant models were examined. Stratification on gender, race, ethnicity and socioeconomic status was explored.
RESULTS:
The association with ozone and PM2.5 were strongest on the day of the emergency department visit (RRIQR=1.05, 95% CI 1.04-1.06) and (RRIQR=1.03, 95% CI 1.02-1.04), respectively, with a decreasing effect across lags. The largest effect size due to tree pollen came from using the 5-day moving average (RRIQR=1.23, 95% CI 1.21-1.25). Weed pollen also showed the highest effect with the 5-day moving average (RR10=1.13, 95% CI 1.12-1.14). Grass pollen was only minimally associated with the outcome while ragweed had a negative association.
CONCLUSIONS:
Ambient air pollutants ozone and PM2.5 are associated with increases in pediatric emergency department asthma visits during the warm weather season. The different pollen types showed different associations with the outcome. High levels of tree and weed pollen appear to be important risk factors in asthma exacerbations.