Has the Impact of Heat Waves on Mortality Changed in France Since the European Heat Wave of Summer 2003?

A. Fouillet; G. Rey; V Wagner; K. Laaidi; P. Empereur-Bissonnet; A. Le Tertre; P. Frayssinet; P. Bessemoulin; F. Laurent; P. De Crouy-Chanel; E. Jougla; D Hémon

Disclosures

Int J Epidemiol. 2008;37(2):309-317. 

In This Article

Abstract and Introduction

Abstract

Background: In July 2006, a lasting and severe heat wave occurred in Western Europe. Since the 2003 heat wave, several preventive measures and an alert system aiming at reducing the risks related to high temperatures have been set up in France by the health authorities and institutions. In order to evaluate the effectiveness of those measures, the observed excess mortality during the 2006 heat wave was compared to the expected excess mortality.
Methods: A Poisson regression model relating the daily fluctuations in summer temperature and mortality in France from 1975 to 2003 was used to estimate the daily expected number of deaths over the period 2004–2006 as a function of the observed temperatures.
Results: During the 2006 heat wave (from 11 to 28 July), about 2065 excess deaths occurred in France. Considering the observed temperatures and with the hypothesis that heat-related mortality had not changed since 2003, 6452 excess deaths were predicted for the period. The observed mortality during the 2006 heat wave was thus markedly less than the expected mortality (~4400 less deaths).
Conclusions: The excess mortality during the 2006 heat wave, which was markedly lower than that predicted by the model, may be interpreted as a decrease in the population's vulnerability to heat, together with, since 2003, increased awareness of the risk related to extreme temperatures, preventive measures and the set-up of the warning system.

Introduction

In August 2003, Western Europe experienced a heat wave that was exceptional in terms of duration, intensity, geographic extent and health impact.[1–5] In France, this event revealed an overall lack of reactivity by people (insufficient protective reflexes and help for the elderly), health professionals (poorly known diseases related to heat), the health system (difficulty perceiving the signals, lack of prevention recommendations) and the media (alarmist messages but no information on prevention).

In order to prevent the consequences of a new heat wave, a National Heat Wave Plan was set up by the Directorate General for Health to prevent the risks related to extreme temperatures.[6] The plan includes several measures: set-up of a system for real-time surveillance of health data, compilation of scientific recommendations on the prevention and treatment of heat-related diseases, air-conditioning equipment for hospitals and retirement homes, drawing up of emergency plans for retirement homes, city-scale censuses of the isolated and vulnerable, visits to those people during the alert periods, and set-up of a warning system. All the Directorates General of the Ministry of Health were involved together with the Directorate General for Civil Defence and Security.

During alert periods, other specific measures are to be implemented: intensification of care offer, visits to isolated and vulnerable people, and repeated preventive message broadcasting by the media.

Since summer 2004, the French Institute for Health Surveillance (Institut de Veille Sanitaire: InVS), in close collaboration with the national weather service (Météo-France), defined and implemented a heat health watch warning system on the basis of biometeorological indicators[7] and other criteria.[8] The warning system operates from 1 June to 31 August (seasonal surveillance period). When the alert criteria are fulfilled, an awareness and action level is declared by the Prefect who manages the département (French administrative unit with an average population of 600 000). A third level (maximum mobilization) is implemented if the impacts of the heat wave overwhelm the health field: power cuts, drought, management problems in the funeral centres and heavy air pollution.

During an alert period and after it, the health impacts of the heat wave are estimated by comparing the observed and expected numbers of deaths. This comparison does not take into account the temporal pattern of temperatures. The national heat plan and the warning system are evaluated and improved each year (feedback from the various players, outside evaluation, exercises).

The alert system aims to give the public authorities 3 days’ prior warning that a heat wave may occur, in order for the National Heat Wave Plan measures to be put into operation. The preventive measures and the new alert system are aimed at modifying the behaviour of people, health institutions and health authorities with regard to high summer temperatures.

In July 2006, a severe heat wave occurred over a large part of France and lasted 18 days (11–28 July). It also affected other European countries.[9] According to Météo-France, this event was the second most severe heat wave recorded since 1950; the 2003 heat wave was the most severe. The intensity and duration of the 2006 heat wave were similar to those of the 1976 heat wave in France, during which 5000 excess deaths occurred.[10]

The objective of the study was to predict the national daily mortality for the summers of 2004–2006 and to compare it to the observed mortality, using a model based on a combination of temperature indicators for the same day and the 10 preceding days. The model was built using the data from a 29-year period, from 1975 to 2003.[11] The number of excess deaths observed during the 2006 heat wave was thus estimated and compared with the expected number of excess deaths, assuming that the relationship between temperature and mortality during summer 2006 was similar to that observed during the summers of 1975–2003. This comparison was intended to contribute to assessing the health impact of the prevention and alert measures, and the population's general awareness due to the 2003 heat wave.

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