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Lucas M. Neas,^1,2,3 Joel Schwartz,^1,3 and Douglas Dockery^1,3

¹Environmental Epidemiology Program, Department of Environmental Health; and ²Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA
³Channing Laboratory, Department of Medicine, Brigham and Womens Hospital, Harvard Medical School, Boston, Massachusetts, USA

Abstract

This study reassessed Schwartz and Dockery's analysis of daily mortality from nonexternal causes among residents of Philadelphia, Pennsylvania, over 8 years, from 1973 to 1980 [American Review of Respiratory Disease 145:600-604 (1992) ]. A Poisson regression analysis using the same model found that a 100-µg/m³ increment in the 48-hr mean concentration of total suspended particulates (TSP) was associated with increased all-cause mortality [rate ratio = 1.069 ; 95% confidence interval (CI) , 1.043-1.096) after adjustment for quadratic trend, season, year, previous day's mean temperature, dew point, winter temperature, and indicators of hot (temperature > 80°F) and humid days (dew point > 66°F) . Critics suggested that time-varying factors such as season and day of week were not sufficiently controlled in this analysis and subsequent studies in other locations. We used a conditional logistic regression analysis with a case-crossover design to reanalyze the data, with air pollution in the prior and subsequent weeks to the day of death serving as referent periods. The case-crossover approach controls for season and day of week by design rather than modeling. We found that a 100-µg/m³ increment in the 48-hr mean level of TSP was associated with increased all-cause mortality [odds ratio (OR) = 1.056 ; CI, 1.027-1.086) after adjustment for the same weather variables as above. Similar associations were observed for deaths in individuals over 65 years of age (OR = 1.074 ; CI, 1.037-1.111) and for deaths due to cardiovascular disease (OR = 1.063 ; CI, 1.021-1.107) . The current case-crossover analysis confirms the general conclusion of the previous Poisson regression analysis of an association of TSP with daily mortality in Philadelphia, Pennsylvania. Key words: air pollutants, case-crossover, mortality. Environ Health Perspect 107:629-631 (1999) . [Online 24 June 1999]

http://ehpnet1.niehs.nih.gov/docs/1999/107p629-631neas/ abstract.html

Address correspondence to J. Schwartz, Department of Environmental Health, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115 USA. Telephone: (617) 432-1245. Fax: (617) 277-2382) . E-mail: joel@sparc6b.harvard.edu

L.N. was supported in part by U.S. Environmental Protection Agency cooperative agreement CR-821762. J.S. and D.D. are supported in part by NIEHS grant ES 0002, and J.S. is supported in part by NIEHS grant ES 07410.

Received 11 January 1999 ; accepted 23 March 1999.