An exceptional heat wave, notable for its intensity and duration, struck mainland France between August 4 and 12, 2003, making that year the hottest in 53 years. Across all French regions, two-thirds of weather stations recorded temperatures above 35°C, and in 15% of French cities, temperatures even exceeded 40°C. In Paris, the 35°C threshold was exceeded for 10 days, including 4 consecutive days between August 8 and 11, 2003—a situation not observed since 1873. Furthermore, the all-time record for the minimum temperature was broken in Paris on August 11 and 12, 2003, with two consecutive nights exceeding 25.5°C. At the same time, the high temperatures and sunshine, combined with pollutant emissions, led to a significant increase in ozone levels in the air. The effect of air pollution must therefore be taken into account in the assessment of the health consequences of the heat wave conducted by the French Institute for Public Health Surveillance (InVS). The French Institute for Public Health Surveillance has launched several epidemiological studies to understand the health consequences of the August 2003 heat wave. A progress report presenting the initial results of these studies is available at www.invs.sante.fr. The August 2003 heat wave had very severe health consequences in France, with mortality primarily affecting the elderly. As early as August 13, 2003, data indicated that a large-scale epidemic was developing. The InVS then estimated an excess mortality of 3,000 cases based on data provided by general funeral homes. A more comprehensive analysis of excess mortality in August was subsequently based on death certificates submitted to the DDASS by city halls. By comparing the number of deaths occurring between August 1 and 15, 2003, in metropolitan France (32,065 reported deaths) with the number of deaths expected for the same period—estimated based on mortality rates in 2000, 2001, and 2002 and adjusted for variations in the age structure of the population (20,630 expected deaths), excess mortality was provisionally estimated on August 26, 2003, at 11,435 deaths, representing a 55% increase in total mortality between August 1 and 15. The central and northern regions of France appear to be more affected by excess mortality. However, this analysis will need to be further investigated. A survey led by the InVS, focusing on heatstroke deaths in public and private healthcare facilities, has been launched. As of August 24, 2003, 2,417 heatstroke deaths had been recorded for the period from August 8 to 19, 2003. The initial results of this non-exhaustive study highlight the vulnerability of the elderly, particularly those over 75 years of age (81% of deaths). Among those who died before the age of 60, the high prevalence of mental illnesses suggests that this is a risk factor, as are obesity and associated conditions. There is also a 13% excess mortality rate among men compared to women. However, this study does not allow for the identification of specific risk factors, nor does it determine to what extent those who died would have survived longer in the absence of such a climatic event. A survey of emergency medical services (university hospitals, SAMU, fire departments, SOS Médecins) between May 25 and August 19, 2003, shows an increase in activity during heatwave periods. The data provided by these services allow for the regular monitoring of highly sensitive indicators (number of heat-related illnesses, interventions involving people over 80 years of age, etc.). Warning signs became apparent starting August 5, 2003, and sometimes later depending on the region. These factors must be taken into account when developing an alert system, which should rely on a broad network of computerized emergency services. A study of mortality in 13 major French urban areas reveals significant disparities between cities, with some showing a clear peak in excess mortality during the heat wave (Paris, Lyon) and others appearing to have been spared (Lille, Nice, Rennes, etc.). These initial observations must be supplemented, particularly by a more detailed analysis of the correlation with meteorological and pollution data. To detect any delayed effects resulting from the heat wave, an alert system based on emergency department data has been established. Indeed, a number of medical conditions can arise in the aftermath of a heat wave. As of August 26, 2003, no significant change in the incidence of these conditions had been observed. This study continued from August 21 to September 1, 2003. An assessment of the health impact and management strategies for the heat wave in neighboring countries was conducted and updated weekly. None of the nine countries contacted was able to provide a consolidated assessment as of August 27, 2003. However, the impact of the heat wave appears to be significant in Portugal, Spain, and the United Kingdom. The contacts established during this process should enable the creation of a network to compare, and even harmonize, studies and their results at the European level. A research program initiated between the InVS and the mission led by Mr. Denis Hémon and Mr. Eric Jougla of INSERM will allow for further development of the ongoing work. (R.A.)