The association between elevated temperatures and mortality has
been reported since the early 20th century [1,2]. The actual magnitude
of heat-related mortality may be greater than reported, since heat-related
deaths are not well defined and heat is usually not listed on death certificates
as causing or contributing to death [3,4,5]. heat waves, because of their
magnitude and duration, offer unique opportunities to study this association.
Much of the excess mortality from heat waves is related to cardiovascular
and other chronic diseases [6,7] and is concentrated in the elderly [1,2,8].
The impact of heat waves on mortality seems also to be higher in urban
areas, due to the ‘urban heat island effect’ [9,10,11]. Some
studies suggest that this effect could be due to interaction between
temperatures and air pollution .
In 1991 and 1995 Spain experienced two heat waves, both associated with
excess mortality [13-17]. However, heat-related mortality was not considered
to be a public health priority in Spain, and specific warning and/or
surveillance systems were not implemented .
During the summer of 2003 Europe experienced a heat wave that was remarkable
both in the magnitude and the duration of the high temperatures recorded.
Thousands of deaths were associated with this meteorological phenomenon,
highlighting the current inabiligy to deal with this kind of health threat.
This paper presents a summary of the results of the study to describe
mortality and detect any excess mortality experienced in summer 2003
in Spain that was carried out by the Instituto de Salud Carlos III.
The heat wave of 2003 in Spain
Summer temperatures in Spain are usually high. The mean daily temperature
during the period 1971-2000 for June, July and August for 48 out of the
50 provincial capitals was 21.8ºC. Mean maximum and minimum temperatures
for the same period were 28ºC and 15.7ºC respectively (Instituto
Nacional de Meteorología).
However, Spain experienced an increase in temperatures during the summer
2003. Mean daily temperatures for the period June-August, in the same
group of cities, were 12.9% (2.7ºC) higher than the observed mean
of the period 1971-2000. Mean maximum and minimum temperatures for the
same period were 11.2% (3ºC) and 16.2% (2.3ºC) higher respectively
compared with the series 1971-2000.
Increased mean and mean minimum temperatures during this period were
registered in all 48 provincial capitals (range: 3.7% to 33.1% for mean
temperatures and range: 2.7% to 24.8% for minimum temperatures) and all
but one registered increased mean maximum temperatures (range: -0.6%
to 23.7%) during the period June-August 2003.
Mean daily temperatures of 33ºC and over were recorded for at least
half of the days (46/92 days) of the period in 15 out of 48 cities. In
8 of these 15 cities temperatures over 33ºC were registered for
more than 60 of the 92 days in the period.
In order to estimate any possible excess in mortality in Spain
in summer 2003, we compared observed mortality during the period July-August
2003 with expected mortality in the provincial capitals of the 50 provinces
Through a query made to the database at the Ministerio de Justicia (Ministry
of Justice), observed mortality was obtained for 27 computerised death
registers . The remaining 23 death registers were not computerised, and
teams of two people travelled to the provincial offices to obtain the
desired data, which was then inserted into the study database. We collected
information on date of birth and death, place of death, and place of
residence at death for every death certificate entered in the death register
between 1 June and 20 August 2003.
To estimate the expected mortality, the Instituto Nacional de Estadística
(National Statistics Institute, INE) provided time series of deaths from
1980 to 2002 (2002 data were provisional) for the 50 cities included
in the study. For the prediction of deaths in 2003 we have fitted Poisson
regression models for different time periods including the year of death
as a continuous variable. Age in five year groups (with the oldest group
being ‘85 years and over’) and month of death were also included
in the model to adjust predictions for variations in age structure of
the population and seasonality. Models better fitting observed mortality
in the first 5 months of 2003 were based on the 1996-2002 and 1990-2002
time periods. We used models using both time series for each one of the
50 cities included in the study and for each one of the following age
groups: 64 years and under, 65 to 74 years, 75 to 84 years, 85 years
Observed number of deaths were compared with expected and the percent
variation was calculated for every city ([O-E/E]*100). An overall weighted
mean percent variation, using expected number of deaths for each city
as weighting variable, was also calculated.
The 50 cities included in the study represent 35% of the total
population and all climate spectra in Spain. Median population per city
is 152 690 inhabitants with a range between 31 506 and 3 016 788 inhabitants.
Of all deaths registered in Spain in the period 1980-2002, 48.7% were
registered in this group of cities. In the year 2002 this percentage
There is great variability in the daily number of deaths registered
in Spain. However, time series show a marked seasonality with peaks in
winter months. Smaller peaks are observed in summer months. The increasing
trend observed since 1980, probably due to the aging of the population,
and to a lesser degree to population growth, seems to have stabilised
in recent years [FIGURE 1]. The year of mortality trend stabilisation
varies from one city to another.
During June-August 2003 a total of 43 212 deaths were registered in
the 50 provincial capitals under study. Of these, 14 236 (33%) occurred
in June, 13 895 (32%) in July and 15 081 (35%) in August. For 141 deaths,
the date of birth was not available. For the 43 071 deaths for which
age could be calculated, 13 039 (30%) were of people aged 85 years or
older, 13 831 (32%) were of people aged 75 to 84 years, 7888 (18%) were
of people aged 65 to 74 years, and 8312 (19%) were of people aged 64
years and under.
Figure 2 shows daily deaths, a 5 day moving average of daily deaths,
and mean daily temperatures in the 50 cities under study during summer
2003. In this figure we observe a peak in daily deaths during the second
week of August. Two smaller peaks, in mid-June and during the second
week of July are also observed. The three peaks observed in daily deaths
coincide with the three waves of high temperatures suffered along the
summer. Although there is an important variability in daily deaths and
temperatures registered among the provincial capitals included in the
study, the pattern observed in figure 2 is applicable to most of them.
Tables 1 and 2 show the total expected and observed deaths and estimated
excess mortality percent for the 50 provincial capitals and for the two
time periods better predicting expected deaths (1996-2002 and 1990-2002).
Excess deaths in summer 2003 compared with expected is 10.6% (4151 deaths)
higher than expected using as predictor the model based on the1996-2002
time series and 7.9% (3166 deaths) using as a predictor the model based
on the 1990-2002 time series.
Assuming that 48% of deaths were registered in the provincial capitals
(data for 2002) we can estimate between 6595 and 8648 excess deaths in
Spain from 1 June to 20 August 2003, using the 1990-2002 or 1996-2002
time series respectively for our model.
Although results using both models, based on the 1990-2002 and 1996-2002
time series, do not differ very much, we consider that the later time
series (1996-2002) better estimates expected deaths because of the stabilisation
of the mortality trend in the last few years. The following results refer
only to the comparison with the model based on the 996-2002 time series.
The excess deaths were higher in August (17% more than expected), but
observed deaths were more than expected for the three months under study
(9% in June and 5% in July) [TABLE 3]. Only the elderly were affected
and important decreases in mortality were registered in people under
65 years throughout the entire period, while we observed 29% excess deaths
among people 85 years and over [TABLE 3].
Table 4 shows expected and observed deaths and estimated mortality difference
percent for the period January- August 2003. Deaths registered in January
and February, and to a lesser extent in March, were fewer than expected.
However, the excess detected in the summer period overcompensated for
this difference and for the first 8 months of 2003 we detected 1964 (1.7%)
more deaths than expected.
Observed deaths in June, July and August 2003 in Spain were
between 7.9% and 10.6% higher than expected. Although excess mortality
was more important in August, excess deaths were observed from June.
Significant excess mortality was observed only in the elderly (75 years
and older), while among those 64 years and younger, mortality decreased
during this period. Access to air conditioning at work and use of swimming
pools and other practices that lower body temperature among younger
people could account for part of this reduction. Further studies of
mortality in people aged 74 years and under are needed to explain these
The objective of this study was to estimate any excess mortality experienced
in Spain during summer 2003. An association between mortality and temperatures
or other variables such as ozone and other pollutants has not been tested.
However, the known association between high temperatures and mortality,
the fact that the three heat waves experienced in Spain in the summer
of 2003 occurred near in time to the three periods of high mortality
registered and the distribution of this high mortality throughout the
country reinforce the hypothesis of this association.
Based on these results, estimated excess deaths in Spain could be between
6595 and 8648. However, this study included data from provincial capitals
and therefore, although they cover a wide range of city sizes, the urban
heat island effect [9,10,11] described in the literature could account
for part of this excess mortality, and results would not be representative
of mortality in Spain, because it may differ in rural areas.
A second study of mortality carried out by the Instituto de Salud Carlos
III in a random sample of 107 out of 7458 rural villages with fewer than
10 000 inhabitants, representing a total of 140 807 people, estimated
a 40% increased mortality compared with the mean mortality observed in
the three previous years (2000-2002) . This study strengthens the
magnitude of the results presented in this article.
Mortality experienced in Spain during the winter of 2002-2003 was marginally
less than mortality observed during the previous winter. It could be
argued that people who unexpectedly did not die during the preceding
winter were the people who died during the summer. Data from a newly
established mortality surveillance system (not presented in this article)
show an excess mortality in the months following the summer, probably
associated to an early appearance of the 2003-2004 influenza season.
These results would not support the ‘harvesting’ theory.
Population groups at high risk, such as people 85 years and older, as
identified in this study and possibly because of the mechanisms explained
by Kenney et al  and Foster et al , can be identified and specific
preventive measures aiming exposure reduction can be implemented if good
coordination between surveillance and alert systems and social and health
services is achieved.
Results of several studies showing the association between high temperatures
and mortality during heat waves in several cities in Spain were published
during the 1990s. However, the magnitude and media coverage, and therefore
the social impact of the heat wave experience in summer 2003 transferred
the debate from academia to the community and political arena.
This debate has altered decision makers’ perception of heat-related
health problems and the control of heat-related mortality has become
a priority. For summer 2004 the Spanish government launched the Plan
de acciones preventivas contra los efectos del exceso de temperaturas
sobre la salud (Prevention plan against adverse effects on health of
high temperatures) , improved for the summer 2005 and created an
interministerial steering commission for this initiative. This plan included:
- A temperature-based alert system using as alert threshold the 95th
centile of observed daily maximum temperatures during the last 25 years.
- Awareness campaigns addressed to high risk groups, the general population
and healthcare and social services professionals.
- A voluntary register of people at high risk who could benefit from
support activities delivered by the Red Cross and other social organisations.
- Development of conduct protocols during heat waves for healthcare and
social services professionals.
- A daily mortality surveillance system.