THE RELATIONSHIP OF URGENT HOSPITAL ADMISSIONS FOR RESPIRATORY ILLNESSES TO PHOTOCHEMICAL AIR-POLLUTION LEVELS IN MONTREAL

The relationship between the number of daily urgent hospital admission s for respiratory illnesses (31 hospitals) and ambient air pollution i n Montreal, Canada, was investigated for warm periods between 1984 and 1988. Air pollutants included I-hr and 8-hr maximum ozone, estimated particulate matter less than or equal to 10 mu m in aerometric diamete r (PM(10)), and estimated sulfate (SO42-) fraction of PM(10). Regressi on analyses controlled for seasonal and day-of-week trends, autocorrel ation, temperature, and relative humidity. For July and August periods , there was a statistically significant (P < 0.01) univariate relation ship of all respiratory admissions to 8-hr maximum ozone, which became nonsignificant when coregressed with temperature. Levels of ozone whi ch never exceeded the U.S. National Ambient Air Quality Standard (NAAQ S) of 120 ppb and high intercorrelations between ozone, particulates, and temperature may explain this finding. Asthma admissions in the May -October periods increased by 2.7% over mean levels for each 12 mu g/m (3) increase in PM(10) levels 3 days prior to the admission day (95% c onfidence interval, 0.7 to 4.8%). In the July and August periods, hosp ital admissions for respiratory illnesses excluding asthma were 9.6% h igher (95% confidence interval, 0.5 to 18.7%) when estimated SO42- had exceeded 8.1 mu g/m(3) 4 days prior to the admission day compared to days when SO42- was at or below this level. There were no significant (P < 0.05) associations of a reference group of nonrespiratory admissi ons to air pollution after controlling for weather. The above results were found despite levels of PM(10) which never exceeded the NAAQS of 150 mu g/m3. The associations found are relevant to public health, sin ce hospital admissions are expected to be accompanied by considerably more frequent occurrences of less serious outcomes. The present findin gs suggest that particulate air pollution during photochemically activ e periods is related to respiratory morbidity in Montreal. (C) 1994 Ac ademic Press,Inc.