The higher air temperature was closely associated with higher ambulance transports due to heat stroke in elderly Japanese

doi:10.4236/ojepi.2011.11001

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Open Journal of Epidemiology, 2011, 1, 1-4

doi:10.4236/ojepi.2011.11001 Published Online November 2011 (http://www.SciRP.org/journal/ojepi/

OJEpi

Published Online November 2011 in SciRes. http://www.scirp.org/journal/OJEpi

The higher air temperature was closely associated with higher

ambulance transports due to heat stroke in elderly Japanese

Nobuyuki Miyatake*, Noriko Sakano, Shoko Murakami

Department of Hygiene, Faculty of Medicine, Kagawa University, Miki, Japan.

Email: *[email protected]

Received 7 October 2011; revised 12 November 2011; accepted 20 November 2011.

ABSTRACT

To investigate the link between higher air tempera-

ture and ambulance transports due to heat stroke,

especially in elderly subjects, using daily data in Sai-

tama prefecture in August, 2010, Japan. We obtained

daily data of air temperature in Saitama prefecture

in August, 2010, Japan from Japan Meteorological

Agency. Number of ambulance transports due to heat

stroke was also used by Saitama prefecture official

website. The effect of high air temperature on ambu-

lance transports due to heat stroke was evaluated. A

total of 1688 ambulance transports due to heat stroke

was observed in Saitama prefecture in August, 2010,

Japan. Seven hundred and twenty one subjects

(42.7%) were over the age of 65. Mean air tempera-

ture, the highest air tempera ture and day light hours

were significantly associated with ambulance trans-

ports due to heat stroke in total subjects (mean air

temperature: r = 0.749, p < 0.0001) and the over the

age of 7. In addition, by separate analysis as classified

by age groups, the correlation coefficient between

ambulance transports due to heat stroke and mean

air temperature was the highest in subjects with over

65. However, the lowest air temperature was not cor-

related with ambulance transports due to heat stroke.

Higher air temperature was closely associated with

higher ambulance tran spo rts due to heat stroke usi ng

daily data in Saitama prefecture in August, 2010, Ja-

pan, especially in elderly subjects.

Keywords: Air Temperature; Ambulance Transports;

Heat Stroke; Saitama Prefecture; Japan

1. INTRODUCTION

Heat stroke in summer in Japan has become public

health challenge in Japan. We have previously showed

that positive changes in air temperature in some areas in

Japan [1,2]. Higher air temperature was closely associ-

ated with higher ambulance transports by monthly data

in Takamatsu [3] and Okayama [4] areas, Japan. By us-

ing daily data, significant relationship between high air

temperature and high ambulance transports was noted in

Osaka area in August, 2009, Japan [5]. In addition, we

explored, by ecological study, the link between high air

temperatures and ambulance transports due to heat

stroke in 47 prefectures, Japan [6]. However, the relation

between high air temperature and ambulance transports

by heat stroke by using daily data still remain to be in-

vestigated. In addition, separate analysis classified by

age groups in the link between high air temperature and

heat stroke is urgently required.

Therefore, in this study, we evaluated the link between

air temperature and ambulance transports due to heat

stroke using daily data, especially in elderly subjects, in

Saitama prefecture in August 2010, Japan.

2. METHODS

Study area. Saitama prefecture is an inland prefecture

situated on the northern border of Japan’s capital. As

large-scale industrial parks were built in former Omiya

(presently Saitama City), Fukaya, Kawagoe, Sayama,

and other cities, Saitama evolved from an agricultural

prefecture into one whose economic activity is based on

industry. Saitama's population surpassed the 7-million

mark in 2002, more than 3 times the 1950 of 2.14 mil-

lion [7].

Ambulance data. Daily incidence data of ambulance

transports due to heat stroke in Saitama prefecture, Japan

was obtained from Saitama Prefecture Official Web page

from August 1 to 31, 2010 [8]. These data are consisted

of number of transfers and the particular reason for heat

stroke.

Meteorological parameters. Daily meteorological pa-

rameters in Saitama prefecture, Japan for the required

periods were obtained from Japan Meteorological Agen-

cy [9]. The observation spots (Saitama city) were located

at the central and the biggest city in the area. Daily me-

N. Miyatake et al. / Open Journal of Epidemiology 1 (2011) 1-4

teorological parameters i.e. mean air temperature (˚C),

the highest air temperature (˚C), the lowest air tempera-

ture (˚C), and daylight hours (hours) were used for

analysis.

Statistical analysis. Simple correlation analysis was

used to test the significance of the linear relationship

among continuous variables. In addition, x2 test was

performed: p < 0.05 was considered to be statistically

significant.

3. RESULTS

Clinical parameters are summarized in Ta bl e 1. A total

of 1688 ambulance transports due to heat stroke was

observed through August, 2010 in Saitama prefecture.

Seven hundred and twenty one subjects (42.7%) were

over the age of 65 and 771 subjects (45.7%) were aged

18 - 65 years, 189 subjects (11.2%) were aged 7 years -

18 years and 7 subjects (0.4%) were under the age of 7.

Mean air temperature was 29.4˚C ± 1.2˚C among obser-

vation period.

We evaluated the relationship between ambulance

transports due to heat stroke and air temperatures and

daylight hours (Table 2). In total subjects, ambulance

transports due to heat stroke was significantly correlated

with mean air temperature (r = 0.749, p < 0.0001) (Figure

1), the highest air temperature and daylight hours. How-

ever, the relationship between ambulance transports due to

heat stroke and the lowest air temperature was not noted.

We further analyzed separate analysis by classified by

age groups. Except under the age of 7, ambulance trans-

ports due to heat stroke were significantly correlated

with mean air temperature, the highest air temperature

and daylight hours. The correlation coefficient between

ambulance transports due to heat stroke and mean air

temperature was the highest over 65 among variables

(Ta ble 2 , Figure 2). Finally, we evaluated the relation-

ship between mean air temperature and number of persons

transported per day as classified by age group using x2

Table 1. Clinical characteristics in Saitama prefecture in August, 2010, Japan.

Mean ± SD minimum maximum

Number of days 31

Ambulance transports due to heat stroke

Average number of persons transported per day 54.5 ± 36.9 8 170

<7 (years old) 0.2 ± 0.4 0 1

7≤ <18 6.1 ± 4.9 0 21

18≤ <65 24.9 ± 19.5 3 93

65≤ 23.3 ± 14.4 3 62

Mean air temperature (˚C) 29.4 ± 1.2 26.3 31.4

The highest air temperature (˚C) 34.5 ± 2.2 29.4 37.9

The lowest air temperature (˚C) 25.5 ± 1.1 23.6 27.3

Daylight hour (hour) 7.4 ± 4.0 0.1 12.3

Ta bl e 2 . Simple correlation analysis between ambulans transports due to stroke and temperature in Saitama prefecture in August,

2010, Japan.

All subjects 7≤ <18 18≤ <65 65≤

r p r p r p r p

Mean air temperature (˚C) 0.749 <0.0001 0.636 0.0001 0.703 <0.0001 0.746 <0.0001

The highest air temperature (˚C) 0.699 <0.0001 0.606 0.0003 0.632 0.0001 0.726 <0.0001

The lowest air temperature (˚C) 0.293 0.1091 0.141 0.4489 0.308 0.0916 0.284 0.1222

Daylight hour (hour) 0.464 0.0085 0.491 0.0051 0.405 0.0239 0.473 0.0072

N. Miyatake et al. / Open Journal of Epidemiology 1 (2011) 1-4

Figure 1. Simple correlation analysis between ambulance trans-

ports due to heat stroke and mean air temperature in Saitama

prefecture in August, 2010, Japan (All subjects).

Figure 2. Simple correlation analysis between ambulance trans-

ports due to heat stroke and mean air temperature in Saitama

prefecture in August, 2010, Japan (Over 65).

Table 3. Relationship between mean air temperature and number of persons transported per day as classified by age group.

Age

<65 65≤ p

<30˚C 327 274

Mean air temperature

30˚C≤ 640 447

0.0759

test (Table 3). Under 30˚C in mean air temperature, eld-

erly subjects over 65 was more transported due to heat

stroke compare to under 65, but not at a significant level

(p = 0.0759).

4. DISCUSSION

The main finding of this study was that we explored the

mean air temperature was closely associated with ambu-

lance transports due to heat stroke using daily data in Japan,

especially in elderly subjects.

By using monthly data in our previous reports [3,4],

mean temperature of maximum air temperatures in a

month was closely associated ambulance transports in

Takamatsu area (r = 0.738, p = 0.0017) [3] and also in

Okayama area, Japan (r = 0.722, p = 0.0024) [4]. By

using daily data, the highest air temperature was signifi-

cantly correlated with total ambulance transports in

Osaka area (r = 0.347, p = 0.0007) [5]. We also found,

by ecological study, that the correlation coefficient be-

tween mean of the highest air temperature and ambu-

lance transports due to heat stroke in 47 prefectures in

August, 2009 was the highest [6]. Our results in this

study were almost similar to our previous reports and the

higher air temperature was critically involved in higher

ambulance transports due to heat stroke. In addition, 721

subjects (42.7%) were over the age of 65 and the corre-

lation coefficient between mean air temperature and

ambulance transports due to heat stroke was the highest.

In addition, under 30˚C in mean air temperature, elderly

subjects over 65 was more transported due to heat stroke

compare to under 65, but not at a significant level. Taken

together, unexpectedly high air temperatures may be

particularly difficult for the elderly.

It is well known that the relation between higher air

temperature and heat-related disease or death. Qiu et al.

reported that an unusually hot spell in 1999 was fol-

lowed by a high mortality rate in Hokkaido, Japan [10].

Bai et al. also showed that the number of unusual deaths

in the summer of 1994 in Osaka, Japan was more com-

pared to those of previous years [11]. Nakai et al. inves-

tigated heat-related deaths in Japan from 1968 through

1994 and heat-related deaths were most prone to occur

on days with a peak daily temperature above 38 degrees

C [12]. They reported that incidence of heat-related

deaths showed and exponential dependence on the num-

ber of hot days [12]. Global average temperatures are

predicted to increase between 1.4˚C and 5.8˚C by the

end of this century [13]. Taken together, we think rea-

sonable to suggest that simply dealing with high air

temperatures in summer in Japan i.e. innovation of the

thermal energy metabolism in cities and individual cop-

ing with high air temperatures might result in the ame-

lioration of ambulance transports and heat stroke in Ja-

pan.

Potential limitations still remain in this study. First,

the link between ambulance transports due to heat stroke

N. Miyatake et al. / Open Journal of Epidemiology 1 (2011) 1-4

and air temperatures, which was noted in this study, may

not apply for the link among individuals. Second, we

could not directly evaluate heat-related diseases or deaths.

Further studies are required to prove such link.

5. CONFLICT OF INTEREST

There is no conflict of interest.

6. ACKNOWLEDGEMENTS

This research was supported in part by research grants from fukutake

science & culture foundation, Japan.

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