The role of air pollution in the relationship between a heat stress index and human mortality in Toronto.
In this study we considered confounding from air pollutants and chronological variables in the relation between humidex, a summer temperature and humidity index, and nonaccidental mortality, from 1980-1996 in Toronto, Canada. Changes in the risk of death by age group, gender, and combined cardiac-respiratory cause of death were estimated for both 1 degree C and 50-95th percentile increases in humidex using a generalized additive linear model. With air pollution terms in the models, relative risk (RR) point estimates narrowly exceeded 1.0 for all groups. Humidex effects were most apparent for females (RR=1.006, 95% CI=1.004-1.008 per 1 degree C humidex and RR=1.089, 95% CI=1.058-1.121 for 50th to 95th percentile humidex). When air pollution was omitted from the model, RR in the 50-95th percentile analysis increased less than 1.71% for all groups except females, for which RR decreased 1.42%. Differences in RR per 1 degree C humidex were all less than 0.12%. Confidence intervals narrowed slightly for all groups investigated. Heat stress has a statistically significant, yet minimal impact on Toronto populations, and air pollution does appear to have a small, but consistent confounding effect on humidex effect estimates.
Rainham
Daniel G C
DG
McLaughlin Centre for Population Health Risk Assessment, University of Ottawa, Ottawa, Ontario, Canada.
Smoyer-Tomic
Karen E
KE
D000367:Age Factors; D000368:Aged; D000393:Air Pollutants / Q000009:adverse effects*; D002248:Carbon Monoxide / Q000009:adverse effects; D005260:Female; D018882:Heat Stress Disorders / Q000401:mortality*; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D006813:Humidity / Q000009:adverse effects*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009585:Nitrogen Dioxide / Q000009:adverse effects; D009864:Ontario; D010126:Ozone / Q000009:adverse effects; D012189:Retrospective Studies; D012621:Seasons; D012737:Sex Factors; D013458:Sulfur Dioxide / Q000009:adverse effects; D014505:Urban Population
D000393:Air Pollutants; D013458:Sulfur Dioxide; D010126:Ozone; D002248:Carbon Monoxide; D009585:Nitrogen Dioxide