The consequences of the heat wave 2003 were probably underestimated in many countries, at least those based on the first estimates. This excess mortality affects vulnerable groups, particularly those who are old or ill. Identification of risk factors is a priority if the necessary prevention actions are to be implemented. The next few decades will be marked by the convergence of three events that will transform the exceptional circumstances of 2003 into a recurrent risk that must be considered as a priority in the EU health policies.
These three events are population trends, air pollution and global warming.
- Population trends: as life expectancy increases, there will be increasing numbers of highly vulnerable people aged 80 years and over. Human population is aging worldwide and that the proportion of those aged over 60 will double in the next 30 years.
This aging trend is most marked in industrialised countries, particularly in Europe.
- Air pollution played an undeniable role in 2003.
The respective roles of temperature and ozone in the excess mortality are difficult to assess. The relationship between ozone pollution and excess mortality was estimated to be between 3% and 85% in nine French towns. The reason for this high heterogeneity between towns remains unclear, and demands further study.
- Analysis of long term meteorological trends carried out in recent years underlines that global warming is a reality, and that more heat waves are highly likely to occur in the future.
It will no longer be possible to express surprise at these climatic events and their consequences. We must reinforce policies for forecast, alert and prevention.
Which was the mortality impact of the 2003 heat wave?
The cumulated excess mortality during summer 2003 has been assessed by the project Etude de l'impact de la canicule d'août 2003 sur la population européenne, coordinated by the INSERM, Montpellier, France, at the request of the European Commission. The study covers sixteen countries. The numbers of deaths are available for each day by gender, age and region (NUTS 2), since January 1st 1998, i.e. 19 098 574 non-empty cells for the daily number of deaths.
To be able to compare the years and European countries with very different population sizes, the daily death frequency in relation to the yearly total number of deaths was calculated. The Project defined standard boundaries. An analysis of the reference period - 1998-2002 - shows that the day only explains between 2% and 3% of the variance in deaths observed during the summer period, whereas the year of observation and the country each explain between 5% and 6%.
Three main mortality peaks are apparent during summer 2003: the peak on 13 June, the double peak on 16-21 July and lastly the peak on 12-13 August which seems exceptionally pronounced. A persistent excess mortality at the end of June and during September was observed. Out of a total of 1 952 summer days corresponding to the sixteen countries studied, 147 exceed the boundaries marking the high extreme values, i.e. 7.5% of the total. Fifty days exceed the boundaries marking the exceptional values. In total, more than 80 000 additional deaths were recorded in 2003 in the twelve countries concerned by excess mortality compared to the 1998-2002 period. Whereas 70 000 of these additional deaths occurred during the summer, still over 7 000 occurred afterwards. Nearly 45 000 additional deaths were recorded in August alone, as well as more than 11 000 in June, more than 10 000 in July and nearly 5 000 in September. The mortality crisis of early August extended over the two weeks between 3 and 6 August; 15 000 additional deaths were recorded in the first week and nearly 24 000 in the second. The excess mortality in this second week reached the exceptional value of 96.5% in France and over 40% in Portugal, Italy, Spain, and Luxembourg. Excess mortality exceeded 20% in Germany, Switzerland, and Belgium and 10% in all the other countries. European regional maps (NUTS 2) outline the early August mortality crisis breaking national frontiers. The crisis caused major distortions in the gender and age structure of death. On August 12th in France the proportion of deaths of the over-95s reached 8.9% of the total, an increase of 46% compared with the expected figure.
These observations suggest that in addition to the exceptional mortality crisis, which occurred at the beginning of August 2003 and which was so large that none could ignore it, there may have been a sequence of minor crises, which passed almost unnoticed. Yet, the cumulative result over the whole summer period can globally be just as significant. In France and Italy the cumulated excess mortality from 1 June to 30 September, 2003 (+19 490 and +20 089 deaths, respectively) have different accumulating profiles. These results suggest that centralising daily deaths on sufficiently large scale, including grouping regions or countries with small populations, should improve the monitoring of summer excess mortality potentially due to global warming.
Source: European Union Project Etude de l'impact de la canicule d'août 2003 sur la population européenne
The regions most affected lie in a south-west north-east axis, from the Algarve in Southern Portugal to Westphalia in Germany. A secondary axis starts in Southern England and continues towards Latium in Central Italy and towards Croatia. The most significant mortality focal spots are in France (Île-de-France and the neighbouring region of Centre), where mortality recorded between 3 and 16 August is double that expected. Six regions—two in Southern Portugal (Algarve and Alentejo) and four in France to the west and east of the Île-de-France and Centre (Pays-de-la-Loire, Poitou-Charentes, Burgundy and Franche-Comté)—recorded a very high excess mortality during these two weeks (between 65% and 125%). The south-eastern boundaries of the mortality crisis are poorly defined as it was not possible to obtain the necessary data in Bosnia-Herzegovina or other countries of the former Yugoslavia.
Source: European Union Project Etude de l'impact de la canicule d'août 2003 sur la population européenne
According to most of the previous studies, the potential mortality impact of heat waves is most likely data and method-driven. Those national studies suggest that the number and magnitude of excess deaths is highly sensitive to the reference period, the time of studied, the choice of age groups and geographical variations. In short, a comparison of the various national studies of the magnitude of 2003, excess mortality across countries becomes extremely difficult due to five major reasons: (1) no universal definitions of a heat wave and different durations of heat waves; (2) different methods used to estimate the magnitude of excess mortality; (3) different period of time studied; (4) different age selections; and (5) different geographic description. No standardized estimates across European countries have been made for the 2003 heat wave event (Kovats and Ebi 2006). To make comparisons of excess mortality in 2003 summer period possible, the foremost pathway is to have the same period of time studies for estimating the excess mortality to the dataset. Second, an appropriate method of estimation shall be used and standardized. Third, when compared to different age groups of excess mortality, the truncation of age groups shall be consistent. Last, a single uniform breakdown of geographic units shall be used for a comparison of excess mortality, not with a city to a country, vice versa.
The EU publication Eurosurveillance has provided a special study about updates and additional context. According to the report in early 2004, an estimated 22 080 excess deaths occurs in England and Wales, France, Italy and Portugal during and immediately after the heat waves of the summer of 2003. To these should be added 6 595-8 648 excess deaths in Spain, of which approximately 54% occurred in August, and 1 400-2 200 in the Netherlands, of which an estimated 500 occurred during the heat wave of 31 July-13 August.
Data for Italy, provided here for the cities of Bologna, Milan, Rome, and Turin, are compatible with the earlier estimate that 3 134 excess deaths occurred in the 21 Italian regional capitals during the period 1 June-15 August; the Italian National Institute of Statistics however, reported an excess of 19 780 deaths country-wide during June-September 2003 as compared to 2002.
Reports elsewhere indicate that approximately 1 250 heat-related deaths occurred in Belgium during the summer of 2003, that there were 975 excess deaths during June-August in Switzerland and 1 410 during the period August 1-24 in Baden-Württemberg, Germany. At this point, it seems reasonable to speculate that with evidence of heat wave-associated deaths beyond England and Wales, France, Italy, and Portugal, the previously published estimate of 22 080 early August excess deaths should be revised upward by at least 50% for all of western Europe, and by 100% or more if heat events that occurred during June and July 2003 are also taken into account.
Experts employed a variety of methods to estimate the number of excess deaths during and just after the 2003 heat episodes and to relate daily death counts to weather, to concentrations of air pollutants, and to demographic and social characteristics. Indeed, the varying emphases and methods demonstrated by the six national contributors provide complementary evidence of what happened in 2003, and to whom. While the absence of uniform methods does limit between-country comparisons of the health impact of the 2003 heat waves, these reports taken together suggest that weather alone does not explain the varying tolls of excess death within and between countries.
All reports demonstrate that the mortality impact of the 2003 heat wave was greatest on the very old: for example, excess mortality in France was estimated at 20% for those aged 45-74 years, at 70% for the 75-94 year age group, and at 120% for people over 94 years. There was no evidence of excess mortality in infants and children in any of the six reports. Among the elderly in France, Portugal and Italy, the three countries which stratified deaths by sex, rates were higher in females.
Investigators in Rome and Turin calculated rates of excess death as a function of socioeconomic level. They report that the greatest excess was in people living in areas of the lowest socioeconomic level, and suggest that finding may be upwardly biased, due in part to the phenomenon that those who have the means to do so leave Italian cities in summer, leading to an overestimate of the denominator for economically advantaged elderly people resident in the city in summer.
It has been observed that few deaths during heat waves are declared to be due to hyperthermia, heatstroke and other classic heat-related illnesses. Reports from both France and Portugal observe that in 2003, deaths certified as caused by ambient heat constituted an important proportion of the death excess; in France, 2 852 of 11 891 (24%) excess deaths among people over 74 years were medically certified as directly heat-related.
Between-city comparisons offer insight into the influence on deaths during heat waves of air pollution, population adaptation, and community preparedness. In Portugal, August forest fires led to a reported 18 accidental casualties: presumably the attendant air pollution may also have had an impact on short-term mortality. Coincident to the high temperatures, elevated concentrations of ground-level ozone and PM10 were recorded in London and the south east of England, those areas of England and Wales where excess mortality was most in evidence. In France, varying concentrations of ground-level ozone in cities subject to differing meteorological circumstances has allowed investigators to assess the joint effects of ozone and heat: these appear to be additive; while the apportionment of deaths to heat versus ozone differed markedly between cities, it appears that for France overall, during the period 3-17 August 2003, heat had the preponderant impact on mortality.
Are those who die during heat waves already near death, with extreme heat advancing the date of their demise by only a few days to weeks, and thus creating a compensatory deficit in expected deaths during the days following the heat event? US investigators have suggested so, and the very high rates of excess death in Europe during 2003 among the very old tend to support that concept. However, while deaths for all ages in England and Wales declined by 4% between 24-29 August when compared with expected numbers, there was no evidence of mortality displacement in France or Spain, neither during late August, nor during September, October, and November.
From the European Union Canicule Project:
• See Report on excess mortality in Europe during summer 2003 - EU Canicule Project - 2007
• See Summary of Data Collection - EU Canicule Project - 2007
From the European Union/WHO EuroHeat Project:
• See Heat waves and public health in Europe - 2006
From the Eurosurveillance report:
• See What lessons can be learnt from the exceptionally long and severe heat wave experienced in Europe in 2003? from Gilles Brücker, Director, Institut de Veille Sanitaire, France
• See The 2003 European heat waves from Tom Kosatsky, Direction de santé publique, Montréal
• See Summary of the mortality impact assessment of the 2003 heat wave in France
• See Mortality in Spain during the heat waves of summer 2003
• See The impact of the summer 2003 heat waves on mortality in four Italian cities
• See The effect of the summer 2003 heat wave on mortality in the Netherlands
• See The impact of the 2003 heat wave on daily mortality in England and Wales and the use of rapid weekly mortality estimates
• See Mortality in Portugal associated with the heat wave of August 2003: Early estimation of effect, using a rapid method
From other sources:
• See The impact of the 2003 heat wave on mortality and hospital admissions in England
• See Mortalidade em Portugal no Verão de 2003: influência das ondas de calor
• See Heat wave 2003 and mortality in Switzerland
• See Die Auswirkungen der Hitzewelle 2003 auf die Gesundheit
• See Impacts of summer 2003 heat wave in Europe
• See The heat wave in France in august 2003: consequences on the level of mortality and on the evolution of the system of production of mortality data
• See Santé: rapport public sur la canicule de l'été 2003
• See Étude des facteurs individuels et des comportements ayant pu influencer la santé des personnes âgées pendant la vague de chaleur de 2003
• See Mortality and displaced mortality during heat waves in the Czech Republic
• See Vpliv vro?inskih valov na umrljivost Vro?inski val avgusta 2003 v Sloveniji - Institute of Public Health of the Republic of Slovenia (in Slovenian only)
• See Effects of the 2003 European heat wave on the Central Mediterranean Sea: surface fluxes and the dynamical response
• See Mortality in southern England during the 2003 heat wave by place of death