Air pollution and hospital admissions for the elderly in Birmingham, Alabama.

Several studies have reported associations between airborne particles and/or ozone and hospital admissions for respiratory disease. This study examined whether such an association could be seen in Birmingham, Alabama, one of the few cities in the United States with daily monitoring of inhalable particles. Daily counts of hospital admissions were computed by date of admission from Medicare records for pneumonia and chronic obstructive pulmonary disease for the years 1986-1989. Classification was by discharge diagnosis. The daily average of ozone and particulate matter with an aerodiameter of < or = 10 microns (PM10) from all monitoring stations in Birmingham was computed. Approximately six admissions for pneumonia and two for chronic obstructive pulmonary disease were observed each day. In Poisson regression analysis controlling for time trends, seasonal fluctuations, and weather, inhalable particles were a risk factor for admission for pneumonia (for an increase of 100 micrograms/m3 in daily concentration, relative risk (RR) = 1.19, 95% confidence interval (CI) 1.07-1.32) and chronic obstructive pulmonary disease (RR = 1.27, 95% CI 1.08-1.50). The results were not sensitive to alternative methods for controlling for seasonal patterns and weather, nor to the exclusion of very hot or cold days. Ozone was more weakly associated with admissions for pneumonia, with a 2-day lag (RR = 1.14, 95% CI 0.94-1.38), and for chronic obstructive pulmonary disease, with a 1-day lag (RR = 1.17, 95% CI 0.86-1.60). The risks are for an increase in ozone exposure of 50 parts per billion. Tests for nonlinearity in the relation between inhalable particles and admissions were not significant, and nonparametric smoothing found no evidence of a threshold in the relation.