This Wednesday, August 24 will be the hottest day of the week, with temperatures exceeding 30°C in places. However, this episode will not be long and intense enough to be qualified as a heat wave, unlike the three previous summer heat waves. Known to affect organisms, high heat has multiple effects: from a simple headache to dehydration, which can go as far as hyperthermia and death. During the 2003 heat wave, more than 15,200 people died because of the heat, according to a study published in 2019 by Public Health France. But how are these results produced?
The creation of the national heat wave plan
After the heat wave of 2003, which was by far the deadliest heat wave in France, the national heat wave plan (PNC) was created. Coordinated by the Ministry of Health, it is activated each year from June 1 to September 15 and is indexed to weather maps produced by Météo France. As long as the departments are in green, simple vigilance is observed.
But when a heat wave occurs – that is to say very high temperatures day and night, for at least three consecutive days – and the departments go into orange or red vigilance, monitoring of health indicators is triggered for the region. This heat wave and health alert system (Sacs) enables Public Health France, one of the health safety organizations that is a member of the PNC, to monitor the impact of heat waves on populations.
Several indicators monitored
This monitoring is based on a wide range of indicators. First of all, on the health monitoring system for emergencies and deaths (Sursaud), which provides indications on the use of emergency care for pathologies directly linked to heat such as hyperthermia, dehydration or hyponatremia (which corresponds to a state of hyper-hydration). Three pathologies grouped under the iHeatwave indicator. This system notably covers visits to the hospital emergency department and SOS Médecins consultations, for all ages.
Monitoring is also based on information collected by labor inspectors, who systematically carry out an administrative inquiry after a fatal accident that has occurred in the workplace. Since the beginning of the summer, six cases of death at work suspected of being linked to the heat wave have been identified.
Excess mortality compared to previous years
These figures are compiled each week by Public Health France during “epidemiological points”, reporting on the impact of the heat wave on mortality. “The excess mortality is estimated by comparison with previous years outside periods of heat waves, in the departments and during periods when the heat wave alert thresholds have been exceeded”, specifies Marie Delibéros, attached to the communication department of Public Health France. Thus, during its point of August 16, the health authority indicates that between July 4 and July 24, « the non-specific surveillance system for emergencies and deaths observes an excess of all-cause mortality of around +20%”.
However, this method “does not provide an estimate of the excess mortality attributable to the heat, but an estimate of the excess mortality compared to previous years, during the heat wave”indicates the organization in its study published in 2019. These estimates are therefore then compared with mortality data from the Center for Epidemiology on the Medical Causes of Death (CépiDc) of the National Institute of Health and Medical Research. (Inserm).
If the results for the summer of 2022 are not yet known, a descriptive and complete assessment of the impact of heat waves on mortality should be published in September, at the end of the national heat wave plan. It will be established “on the basis of consolidated data”, specifies Marie Delibéros, and will take into account “the set of summer heat waves and the concomitant Covid-19 epidemic”.