EFFECTS OF LOW AMBIENT LEVELS OF OZONE AND SULFATES ON THE FREQUENCY OF RESPIRATORY ADMISSIONS TO ONTARIO HOSPITALS

To investigate the acute respiratory health effects of ambient air pol lution, the number of emergency or urgent daily respiratory admissions to 168 acute care hospitals in Ontario were related to estimates of e xposure to ozone and sulfates in the vicinity of each hospital. Ozone levels were obtained from 22 monitoring stations maintained by the Ont ario Ministry of the Environment for the period January 1, 1983 to Dec ember 31, 1988. Daily levels of sulfates were recorded at nine monitor ing stations representing three different networks operated by the Ont ario Ministry of the Environment and Environment Canada, Positive and statistically significant associations were found between hospital adm issions and both ozone and sulfates recorded on the day of admission a nd up to 3 days prior to the date of admission. Five percent of daily respiratory admissions in the months of May to August were associated with ozone, with sulfates accounting for an additional 1% of these adm issions. Ozone was a stronger predictor of admissions than sulfates. P ositive and statistically significant (P < 0.05) associations were obs erved between the ozone-sulfate pollution mix and admissions for asthm a, chronic obstructive pulmonary disease, and infections. Positive ass ociations were also found in all age groups, with the largest impact o n infants (15% of admissions associated with the ozone-sulfate polluti on mix) and the least effects on the elderly (4%). Temperature had no effect on the air pollution-admission relationship. Ozone (lagged 1 da y) and sulfates (lagged 1 day) displayed a positive association with r espiratory admissions for 91 and 100% of the 168 acute care hospitals, respectively. Air pollution was not related to a class of nonrespirat ory admissions, which served as a negative control, nor was it related to admissions in the winter-months of December to March, when ozone a nd sulfate levels are low and when people spend a considerable amount of time indoors. (C) 1994 Academic Press, Inc.