Eurosurveillance - Volume 10, Issue 7, 01 July 2005

What lessons can be learnt from the exceptionally long and severe heatwave experienced in Europe in 2003? First, that these heatwaves can be responsible for a dramatic excess mortality: certainly more than 50 000 excess deaths for Europe in August 2003. The consequences of the heatwave 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 current issue of Eurosurveillance updates and provides additional context to the report in early 2004 of an estimated 22 080 excess deaths in England and Wales, France, Italy and Portugal during and immediately after the heat waves of the summer of 2003 [1]. While estimates for England and Wales [2], France [3], and Portugal [4], are largely unchanged from those reported earlier, to these should be added 6595-8648 excess deaths in Spain [5], of which approximately 54% or 3574-4687 occurred in August, and 1400-2200 in the Netherlands [6], 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 3134 excess deaths occurred in the 21 Italian regional capitals during the period 1 June-15 August [1,7]; the Italian National Institute of Statistics however, reported an excess of 19 780 deaths country-wide during June-September 2003 as compared to 2002 [8]. Reports elsewhere indicate that approximately 1250 heat-related deaths occurred in Belgium during the summer of 2003 [9], that there were 975 excess deaths during June-August in Switzerland [10] and 1410 during the period August 1-24 in Baden-Württemberg, Germany [11]. 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.

During the first two weeks of August 2003, Portugal was affected by a severe heat wave. Following the identification in Portugal of the influence of heat waves on mortality in 1981 and 1991 (estimated excess of about 1900 and 1000 deaths respectively), the Observatório Nacional de Saúde (ONSA) - Instituto Nacional de Saúde Dr. Ricardo Jorge, together with the Vigilância Previsão e Informação - Instituto de Meteorologia, created a surveillance system called ÍCARO, which has been in operation since 1999. ÍCARO identifies heat waves with potential influence on mortality [1]. Before the end of the 2003 heat wave, ONSA had produced a preliminary estimate of its effect on mortality. The results based on daily number of deaths from 1 June to 12 August 2003 were presented within 4 working days. Data was gathered from 31 National Civil registrars, covering the district capitals of all 18 districts of mainland Portugal, and representing approximately 40% of the mainland’s mortality. The number of deaths registered in the period 30 July to 12 August was compared with the ones registered during 3 comparison periods: (in July): 1-14 July, 1-28 July, and 15-28 July). 15-28 July, the period best resembling the heat wave in time and characteristics, produced an estimation of 37.7% higher mortality rate then the value expected under normal temperature conditions. From this value, an estimate of 1316 death excess was obtained for mainland Portugal. The main purpose of this article is to present the method used to identify and assess the occurrence of an effect (excess mortality) during the heat wave of summer 2003.

France experienced a record-breaking heat wave between 2 and 15 August 2003. All the French regions were affected by this heat wave, which resulted in an excess of 14 800 deaths between 1 and 20 August. The increase in the number of excess deaths followed the same pattern as the increase in temperatures. No deviance from the normal death rate was observed in the month of August during the last third of the month, nor during the following three months. There was a clear discrepancy in the impact of the heat wave from city to city. If the effect of duration of consecutive days with high minimal temperatures and deviance with the seasonal normal temperature was patent, this could not explain all of the observed variability of the death incidence. The victims were mainly elderly women older than 75 years. In terms of relative risk and contribution to the global toll, deaths linked to heat were the most important. Based on these results, the French government developed a Heat Health Watch Warning System and set up a preventive action plan for each region in 2004.

The effect of the elevated temperatures on mortality experienced in Europe during the summer of 2003 was observed in several countries. This study, carried out in Spain, describes mortality between 1 June and 31 August and evaluates the effect of the heat wave on mortality. Observed deaths were obtained from official death registers from 50 provincial capitals. Observed deaths were compared with the expected number, estimated by applying a Poisson regression model to historical mortality series and adjusting for the upward trend and seasonality observed. Meteorological information was provided by the Instituto Nacional de Meteorología (National Institute of Meteorology). Spain experienced three heat waves in 2003. The total associated excess deaths were 8% (43 212 observed deaths compared with 40 046 expected deaths). Excess deaths were only observed in those aged 75 years and over (15% more deaths than expected for the age group 75 to 84 and 29% for those aged 85 or over). This phenomenon (heat-associated excess mortality) is an emerging public health problem because of its increasing attributable risk, the aging of the Spanish population and its forecasted increasing frequency due to global warming. The implementation of alert and response systems based on monitoring of climate-related risks, emergency room activity and mortality, and strengthening the response capacity of the social and health services should be considered.

This study evaluates the impact of the 2003 heat wave on cause-specific mortality and the role of demographic characteristics and socioeconomic conditions that may have increased the risk of mortality in four Italian cities: Bologna, Milan, Rome and Turin. Daily mortality counts, for the resident population by age, sex and cause of death were considered. Daily excess mortality was calculated as the difference between the number of deaths observed and the smoothed average. The impact of heat on health is measured in terms of maximum apparent temperature. The greatest excess in mortality was observed in the north west of Italy (Turin, +23% and Milan, +23%). The old (75-84 years) and the very old (85+ years) were the age groups most affected, and when stratifying by sex, the increase in mortality seemed to be greater among females. The greatest excess in mortality was registered in those with low socioeconomic status in Rome (+17.8%) and in those with lower education levels in Turin (+43%). The analysis of cause-specific mortality not only confirms results from previous studies of an increase in heat-related mortality by respiratory and cardiovascular diseases, but also shows a significant excess in mortality for diseases of the central nervous system and for metabolic/endocrine disorders. Results from 2003 highlight the necessity of targeting future prevention programmes at the susceptible sub-groups identified. The introduction of warning systems alongside efficient preventive plans and the monitoring of mortality during heat waves may represent a valid tool for the reduction of heat-related deaths.

In the Netherlands, between 1400 and 2200 deaths in the summer of 2003 may have been heat-related. The fact that the maximum temperatures were lower than in some other European countries, and occurred in less heavily populated areas, may have led to mortality figures that were relatively less dramatic. The temporarily increased death rates are only partly due to a forward shift of mortality. Heat-related mortality was most pronounced among the elderly in nursing homes.

This paper describes a retrospective analysis of the impact of the 2003 heat wave on mortality in England and Wales, and compares this with rapid estimates based on the Office for National Statistics routine weekly deaths reporting system. Daily mortality data for 4 to 13 August 2003, when temperatures were much hotter than normally seen in England, were compared with averages for the same period in years 1998 to 2002. The August 2003 heat wave was associated with a large short-term increase in mortality, particularly in London. Ozone and particulate matter concentrations were also elevated during the heat wave. Overall, there were 2139 (16%) excess deaths in England and Wales. Worst affected were people over the age of 75 years. The impact was greatest in the London region where deaths in those over the age of 75 increased by 59%. Estimated excess mortality was greater than for other recent heat waves in the United Kingdom. The estimated number of deaths registered each week is reported by the Office for National Statistics. The first clear indication of a substantial increase in deaths was published on 21 August 2003. This provided a quick first estimate of the number of deaths attributable to the heat wave and reflected the pattern of daily deaths in relation to the hottest days, but underestimated the excess when compared with the later analysis.