PM10, ozone, and hospital admissions for the elderly in Minneapolis-St. Paul, Minnesota

Several recent studies have reported associations between airborne particles and/or ozone and hospital admissions for respiratory disease. PM10 has rarely been used as the particle exposure measure, however. This study examined whether such an association could be seen in Minneapolis-St. Paul, Minnesota, which has daily monitoring data for PM10. Data on hospital admissions in persons aged 65 y and older were obtained from Medicare records for the years 1986 through 1989. Daily counts of admissions, by admit date, were computed for pneumonia (ICD9 480-487) and chronic obstructive pulmonary disease (COPD) (ICD9 490-496). Classification was by discharge diagnosis. Daily air pollution data from all monitoring stations for ozone and PM10 in Minneapolis-St. Paul were obtained, and the daily average for each pollutant was computed. An average of approximately six pneumonia admissions and two admissions for chronic obstructive pulmonary disease occurred each day. Poisson regression analysis was used to control for time trends, seasonal fluctuations, and weather. PM10 was a risk factor for pneumonia admissions (relative risk [RR] = 1.17, 95% confidence interval [CI] = 1.33-1.02) and COPD admissions (RR = 1.57, 95% CI = 2.06-1.20). Ozone was also associated with pneumonia admissions (RR = 1.15, 95% CI = 1.36-0.97). The relative risks are for an increase of 100 micrograms/m3 in daily PM10 and 50 ppb in daily ozone concentration. Several alternative methods for controlling for seasonal patterns and weather were used, including nonparametric regression techniques. The results were not sensitive to the methods. When days exceeding the National Ambient Air Quality Standard for either pollutant were excluded, the association remained for both pneumonia (RR = 1.18, 95% CI = 1.34-1.03 for PM10, and RR = 1.18, 95% CI = 1.41-0.99 for ozone) and COPD (RR = 1.54, 95% CI = 2.06-1.16 for PM10).