Intracerebral hemorrhage associated with hourly concentration of ambient particulate matter: case- crossover analysis

Shin Yamazaki ^1*, Hiroshi Nitta ², Masaji Ono ³, Joseph Green ⁴ and Shunichi Fukuhara ¹

¹ Graduate School of Public Health, Kyoto University, Japan
² Epidemiology and Exposure Assessment Section, National Institute for Environmental Studies, Japan
³ Environmental Health Sciences Division, National Institute for Environmental Studies, Japan
⁴ Graduate School of Medicine, The University of Tokyo, Japan

^* To whom correspondence should be addressed. E-mail: yamazaki.shin{at}nies.go.jp.

Accepted 29 June 2006

Abstract

Aims: We examined the association of hourly time-lagged concentration of ambient particulate matter and death due to stroke.

Methods: Mortality data for 5 years (January 1990 through December 1994) were obtained from the Ministry of Health, Labour, and Welfare of Japan. Data were used only if the deceased was 65 years old or older at the time of death, if death was attributed to intracerebral hemorrhage or ischemic stroke, and if the deceased lived in one of 13 major urban areas. Hourly mean concentrations of PM7, NO₂, and photochemical oxidants were measured at monitoring stations in the 13 areas. Time-stratified case-crossover analysis was used to examine the data for evidence of triggering stroke mortality.

Results: The 1-hour mean concentration of PM7 measured about 2 hours before death was associated with the risk of death due to intracerebral hemorrhage from April through September (odds ratio=2.40, 95%CI: 1.48-3.89, for exposure to PM7 of more than 200 µg/m³ (threshold)). The higher risk was independent of the 24- hour mean concentration of PM7. PM7 was not associated with death due to ischemic stroke.

Conclusions: Transiently high concentrations of PM7 are associated with death due to intracerebral hemorrhage. Air quality standards or guidelines for particulate matter should be based not only on 24-hour mean concentrations, but also on hourly data.

Keywords: air pollution, cerebral hemorrhage, mortality

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