Association between tree pollen counts and asthma ED visits in a high-density urban center

Background. Asthma exacerbation patterns are cyclic in nature and often correlate with air particle concentrations. Objective. To examine the relationship between asthma-related emergency department (ED) visits and outdoor air quality for pediatric and adult patients in a high asthma prevalence area, the New York City borough of the Bronx. Methods. Numbers of daily asthma-related adult and pediatric ED visits during one complete year (1999) were obtained from the seven major Bronx hospitals. Daily values of nitrogen oxides (NO _x), ozone (O3), sulfur dioxide (SO₂), and pollen counts were acquired. Results. Asthma-related ED visit numbers were highest in December-January and lowest in July. There were three distinct peaks of increased asthma ED visits: winter (December-January), spring (late April-May), and fall (October). The spring peak was the most striking and coincided with high tree pollen counts (tree pollen: r = 0.90, p = .03). We observed a positive correlation between asthma ED visits in the winter and SO₂ and NO_x levels. Winter peaks of SO₂ and NO_x in early December appeared to precede the winter asthma peak. Conclusions. The spring asthma peak is closely associated with increased tree pollen counts, and the asthma increase at this time is likely due to allergic reactions to pollen. No significant associations could be established with the fall peak. The winter peak correlates with elevated SO₂ and NO_x levels.