Characterizing the Effect of Summer Temperature on Heatstroke-Related Emergency Ambulance Dispatches in the Kanto Area of Japan
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Int J Biometeorol (2014) 58:941–948 DOI 10.1007/s00484-013-0677-4 ORIGINAL PAPER Characterizing the effect of summer temperature on heatstroke-related emergency ambulance dispatches in the Kanto area of Japan Chris Fook Sheng Ng & Kayo Ueda & Masaji Ono & Hiroshi Nitta & Akinori Takami Received: 25 March 2013 /Revised: 26 April 2013 /Accepted: 26 April 2013 /Published online: 23 May 2013 # ISB 2013 Abstract Despite rising concern on the impact of heat on with a combined relative risk (RR) of 1.22 (95 % confidence human health, the risk of high summer temperature on interval, 1.03–1.44), increasing to 1.49 (1.42–1.57) at peak heatstroke-related emergency dispatches is not well under- AT. When linear exposure was assumed, combined RR was stood in Japan. A time-series study was conducted to examine 1.43 (1.37–1.50) per degree Celsius increment. Overall asso- the association between apparent temperature and daily ciation was significant the first few times when median AT heatstroke-related ambulance dispatches (HSAD) within the was initially exceeded in a particular warm season. More than Kanto area of Japan. A total of 12,907 HSAD occurring from two-thirds of these initial hot days were in June, implying the 2000 to 2009 in five major cities—Saitama, Chiba, Tokyo, harmful effect of initial warming as the season changed. Risk Kawasaki, and Yokohama—were analyzed. Generalized ad- increase that began early at the fairly mild perceived temper- ditive models and zero-inflated Poisson regressions were used ature implies the need for early precaution. to estimate the effects of daily maximum three-hour apparent temperature (AT) on dispatch frequency from May to Keywords Apparent temperature . Heat . Heatstroke . September, with adjustment for seasonality, long-term trend, Emergency ambulance dispatch . Time-series . Japan weekends, and public holidays. Linear and non-linear expo- sure effects were considered. Effects on days when AT first exceeded its summer median were also investigated. City- Introduction specific estimates were combined using random effects meta-analyses. Exposure-response relationship was found to Hot weather is an environmental hazard with well-documented be fairly linear. Significant risk increase began from 21 °C impact on human health. Rising temperature that leads to more hot days (Intergovernmental Panel on Climate Change 2007; World Meteorological Organization 2012)isexpectedtoex- Electronic supplementary material The online version of this article acerbate future heat-related mortality and morbidity (Cheng et (doi:10.1007/s00484-013-0677-4) contains supplementary material, which is available to authorized users. al. 2008; Doyon et al. 2008;Goslingetal.2009; Knowlton et al. 2007; Martin et al. 2012). The causal association between * : : C. F. S. Ng ( ) K. Ueda H. Nitta high ambient temperature and premature mortality has been Environmental Epidemiology Section, Center for Environmental Health Sciences, National Institute for Environmental Studies, widely established (Armstrong et al. 2011; Anderson and Bell 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan 2011;Goldbergetal.2011; Kim et al. 2006). Heat exposure e-mail: [email protected] has also been linked to increases in cardiovascular and respi- ratory hospital admissions (Lin et al. 2009; Michelozzi et al. M. Ono Center for Environmental Health Sciences, National Institute for 2009;Wichmannetal.2011), emergency ambulance trans- Environmental Studies, Tsukuba, Ibaraki, Japan ports (Alessandrini et al. 2011; Bassil et al. 2011;Dolneyand Sheridan 2006;Goldenetal.2008;Schafferetal.2012), and A. Takami climate-sensitive diseases (Alexander 2013; Bambrick et al. Regional Atmospheric Environment Section, Center for Regional Environmental Research, National Institute for Environmental 2008;Brayetal.2011; Hashizume et al. 2007). These heat- Studies, Tsukuba, Ibaraki, Japan related health consequences constitute considerable burden in 942 Int J Biometeorol (2014) 58:941–948 terms of reduced quality of life, higher cost of healthcare including surveillance and prevention, and loss of productivity in the economic sense (Bambrick et al. 2008). Managing these ’ heat-related health risks remains a challenge even in today s Saitama highly developed nations. In Japan, average summer temperature from June to Tokyo August has been trending upwards since tracking first began Chiba in 1898. An all-time high was documented in the summer of Kawasaki Yokohama 2010, with average temperature higher than the 1971– 2000 historical average by 1.64 °C (Japan Meteorological Association 2010). This particular episode of heat spell was thought to be responsible for the record high heatstroke- related deaths (Tokyo Metropolitan Government 2012)and emergency transports in many cities (National Institute for Environmental Studies 2012). More recently, Japan recorded a surge in the number of heatstroke-related ambulance dispatches (HSAD) in July 2012 at an increase of 17 % country-wide over the same period in the previous year Fig. 1 Study areas (shaded regions) and monitoring stations (stars). Dark outline denotes inland prefecture boundary, while lighter outline (Fire and Disaster Management Agency 2012). The growing denotes city boundary incidence of heat-related disorders is garnering public concerns and at the same time brings increasing attention to period from 2000 to 2009. In Japan, life support ambulances the current prevention strategies (Hoshi and Inaba 2007). are organized by the fire departments. For monitoring of Short-term effect of summer heat on mortality has been ambulance response system, ambulance staffs follow up with previously established in Japan in a multi-region study covering the emergency physicians to keep a record of diagnosis for all Tokyo (Chung et al. 2009). However, the impact of summer transported patients (Abe et al. 2009). Determination of heat- temperature on HSAD has not been assessed in the epidemio- stroke diagnosis was according to the emergency physicians logical context. The pattern and magnitude of this association based on the first presentation of patients at the emergency remain unexplored in Japan. In addition, because HSAD cor- departments. respond to a more responsive indicator of heat effect in a Hourly data for ambient and dew point temperature mea- population due to the stronger association with high tempera- sured at the monitoring stations in each city (Fig. 1) were ture in comparison to mortality (Alessandrini et al. 2011), there acquired from the Japan Meteorological Agency. For Saitama is an interest to understand the time course of the effect of high city, the monitoring station in the northwest was selected ambient temperature on HSAD, particularly when such associ- instead of the one in Tokyo to capture the slightly different ation becomes significant. This information can be helpful climate due to the mountainous feature in the northwest region. when evaluating the relevance of existing prevention guide- Kawasaki and Yokohama shared the same monitoring station lines. Given these motivations, we conducted a population- given the close distance. To measure temperature exposure, we based multi-city time-series study using a 10-year monitoring opted for apparent temperature, an index of perceived temper- data to evaluate the association between ambient temperature ature which incorporates the effect of humidity. This tempera- and HSAD in the Kanto metropolitan area of Japan. ture index can better capture response on health, and has been commonly used to investigate the health impact of weather and air pollutants (Basu 2009; Chung et al. 2009; Kovats and Hajat Material and methods 2008;O’Neill et al. 2005). Hourly apparent temperature was calculated using the formula: apparent temperature=−2.653 + Study region and data (0.994 × temperature) + (0.0153 × dew point temperature2) (Kalkstein and Valimont 1986; Steadman 1979). We computed The five study sites are located in the densely populated Kanto the maximum 3-hour average of apparent temperature as the major metropolitan area. They include the Tokyo metropolis and daily measure of temperature exposure (hereinafter referred to four surrounding designated cities—Saitama, Chiba, Kawasaki, as AT) (Wichmann et al. 2011). and Yokohama—covering approximately 3,257 km2 (1,258 square miles) in area and 19.6 million in population as of 2005 Statistical analysis (Fig. 1). Daily case series of HSAD from May to September were We first examined the lag distribution of AT in association collected from the fire departments in each city over a 10-year with the daily HSAD in each city to determine a suitable Int J Biometeorol (2014) 58:941–948 943 length of temperature exposure. Delayed effect of exposure, temperaturecutoffsrangingfrom21°Cto31°Cwereattempted if any, was included as an average in the regression model. separately for Tokyo to understand the risk of dispatches at lower Assuming daily dispatch counts followed an overdispersed temperature threshold. Poisson distribution (Alessandrini et al. 2011; Basu et al. Analyses were performed in R 2.14.2 (R Foundation for 2005), a semi-parametric generalized additive model Statistical Computing, Vienna, Austria) and Stata 11.2 (StataCorp (GAM) was used to explore the exposure–response relation- LP, College Station, TX, USA) at 5 % statistical significance level. ship based on a pooled dataset (Hastie and Tibshirani 1990; Peng et al. 2006). To investigate possible non-linear associ- ation, AT was smoothed using thin plate regression spline Results