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.
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 2
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
C opyright © 2011 SciRes. OJEpi

3 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 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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