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Warren T. Piver,¹ Mitsuru Ando,² Frank Ye,¹ and Christopher J. Portier¹

¹National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
²National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan

Abstract

Heat stroke is associated with prolonged exposures to high air temperatures that usually occur in the summer months of July and August in Tokyo, Japan. Also during July and August, residents of Tokyo are often exposed simultaneously to high concentrations of air pollutants. To assess the impacts of these combined exposures, daily numbers of heat stroke emergency transport cases/million residents for Tokyo were stratified by gender and three groups: 0-14, 15-64, and > 65 years of age, for the months of July and August in 1980-1995. A regression model was constructed using daily maximum temperature (T_max) and daily average concentrations of NO₂ and O₃ as model covariates. Classification indices were added to make it possible to compare the expected number of heat stroke cases by age and gender. Lag times of 1-4 days in T_max and air quality covariates and terms to account for interactions between pairs of model covariates were also included as additional risk factors. Generalized linear models (GLMs) , assuming a Poisson error structure for heat stroke emergency transport cases, were used to determine which covariates were significant risk factors for heat stroke for the three age groups of males and females. Same-day T_max and concentrations of NO₂ were the most significant risk factors for heat stroke in all age groups of males and females. The number of heat stroke emergency transport cases/million residents was greater in males than in females in the same age groups. The smallest number of heat stroke emergency transport cases/million residents occurred for females 0-14 years of age and the greatest number of heat stroke emergency transport cases/million residents occurred for males > 65 years of age. Key words: air pollutants, generalized linear regression models, heat stroke, maximum daily temperatures. Environ Health Perspect 107:911-916 (1999) . [Online 15 October 1999]

http://ehpnet1.niehs.nih.gov/docs/1999/107p911-916piver/ abstract.html

Address correspondence to W.T. Piver, National Institute of Environmental Health Sciences, MD EC-14, PO Box 12233, Research Triangle Park, NC 27709 USA. Telephone: (919) 541-3471. Fax: (919) 541-2242. E-mail: piver@niehs.nih.gov

We thank the Tokyo Emergency Office and the Japan Environment Agency for supplying data. In addition, we thank Y. Matsumoto and K. Tamura for assistance with compiling and analyzing heat stroke, climate, and air pollution data.

Financial and travel assistance for W.P. were provided by a Science and Technology Agency Fellowship from the Japan Research and Development Corporation and a Japan Environment Agency Eco-Frontier Fellowship from the Association of International Research Initiatives for Environmental Studies.

Received 15 January 1999 ; accepted 6 July 1999.