International Journal of Biometeorology

, Volume 58, Issue 5, pp 941–948 | Cite as

Characterizing the effect of summer temperature on heatstroke-related emergency ambulance dispatches in the Kanto area of Japan

  • Chris Fook Sheng NgEmail author
  • Kayo Ueda
  • Masaji Ono
  • Hiroshi Nitta
  • Akinori Takami
Original Paper


Despite rising concern on the impact of heat on human health, the risk of high summer temperature on heatstroke-related emergency dispatches is not well understood in Japan. A time-series study was conducted to examine the association between apparent temperature and daily heatstroke-related ambulance dispatches (HSAD) within the Kanto area of Japan. A total of 12,907 HSAD occurring from 2000 to 2009 in five major cities—Saitama, Chiba, Tokyo, Kawasaki, and Yokohama—were analyzed. Generalized additive models and zero-inflated Poisson regressions were used to estimate the effects of daily maximum three-hour apparent temperature (AT) on dispatch frequency from May to September, with adjustment for seasonality, long-term trend, weekends, and public holidays. Linear and non-linear exposure effects were considered. Effects on days when AT first exceeded its summer median were also investigated. City-specific estimates were combined using random effects meta-analyses. Exposure-response relationship was found to be fairly linear. Significant risk increase began from 21 °C with a combined relative risk (RR) of 1.22 (95 % confidence interval, 1.03–1.44), increasing to 1.49 (1.42–1.57) at peak AT. When linear exposure was assumed, combined RR was 1.43 (1.37–1.50) per degree Celsius increment. Overall association was significant the first few times when median AT was initially exceeded in a particular warm season. More than two-thirds of these initial hot days were in June, implying the harmful effect of initial warming as the season changed. Risk increase that began early at the fairly mild perceived temperature implies the need for early precaution.


Apparent temperature Heat Heatstroke Emergency ambulance dispatch Time-series Japan 



This work was a part of the Development of Seamless Chemical Assimilation System and its Application for Atmospheric Environmental Materials (SALSA) supported by a grant-in-aid for the Research Program on Climate Change Adaptation (RECCA) by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the Ministry of the Environment (MOE) in Japan. The views expressed in this article are those of the authors and do not necessarily represent the views and policies of the aforementioned organizations.

Supplementary material

484_2013_677_MOESM1_ESM.pdf (120 kb)
ESM 1 (PDF 120 kb)


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Copyright information

© ISB 2013

Authors and Affiliations

  • Chris Fook Sheng Ng
    • 1
    Email author
  • Kayo Ueda
    • 1
  • Masaji Ono
    • 2
  • Hiroshi Nitta
    • 1
  • Akinori Takami
    • 3
  1. 1.Environmental Epidemiology Section, Center for Environmental Health SciencesNational Institute for Environmental StudiesTsukubaJapan
  2. 2.Center for Environmental Health SciencesNational Institute for Environmental StudiesTsukubaJapan
  3. 3.Regional Atmospheric Environment Section, Center for Regional Environmental ResearchNational Institute for Environmental StudiesTsukubaJapan

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