Health. Age, gender, region... five misconceptions about the effects of extreme heat on your health.

An early heatwave threatens a large part of the country this weekend: temperatures are expected to exceed heatwave thresholds in three-quarters of the departments - the duration of the episode remains to be seen.

Public Health France (SPF) has just published the results of a study on 16,361 emergency room visits by 16,050 people, between June ¹ and September 15, 2023. The data comes from "iCanicule," a composite indicator that aggregates the 11 possible diagnoses related to heat throughout the summer (hyperthermia, dehydration, hyponatremia, etc.).

The study covered passages recorded over the entire period , not just during the four orange heatwave alert periods.

Unsurprisingly, in cases of extreme heat, SPF observes that dehydration mainly affects young children (nearly half of patients under 6 years old who are taken to the emergency room). Among the elderly, hyponatremia (a drop in the concentration of sodium in the blood) affects a third of those over 60 - far ahead of hyperthermia and dehydration.

But between the two, the risk is not zero - far from it: more than half of 6-49 year-olds admitted to emergency rooms suffered from hyperthermia (heat stroke). This high proportion "can be explained by the lack of self-perception of risk and the conditions of forced or chosen exposure" (professional activity, voluntary exposure, etc.), indicates Santé Publique France. In short, people who do not feel threatened by heat and/or are unaware of its risks.

No one is immune to the consequences of extreme heat , but the numbers remain incomparable: out of more than 16,000 visits, SPF counted 1,042 children under 6 years old and 11,242 adults aged 60 and over. Between the two, "only" 3,783 people aged 6 to 59. The least affected age group is 30-39, with 6.5 visits to the emergency room per 100,000 inhabitants: this is five times less than for young children, and 30 times less than for those over 80.

Public Health France reminds us that "in the elderly, the frequent presence of chronic pathologies" can be "aggravated" by high temperatures, and that "drug treatments can increase sensitivity to heat" or see their effectiveness "impaired by high temperatures."

While there is no real surprise regarding the age of the patients, there is also a real difference according to their gender: women are, overall, more affected than men.

Across the entire population studied, the figures are clear: fewer than 22 visits to the emergency room per 100,000 inhabitants among men, almost 27 among women - that's 23% more for the latter.

But this seems to reflect an age pyramid that, historically, is mostly "favorable" to women: from 0 to 69 years old, visits to the emergency room related to heatwaves are significantly more frequent among men than women. This is especially true among 30-39 year olds, with 70% more visits for men. It is only beyond 70 years old, particularly among 80-89 year olds, that things reverse.

Almost all patients (98.1%) only presented to the emergency room once in connection with the heatwave. And despite the holidays, more than 90% of visits were made in the region of residence - except in Corsica (68.6%). This may be explained by the relatively short duration of stays compared to the long period studied (three and a half months), but also by vacations taken in their own region, or by a professional activity that particularly exposes them to the heat. During holidays, the population is also more able to choose their times, days, and conditions of discharge than during the rest of the year.

For the whole of France, there were 24.4 visits to emergency rooms per 100,000 inhabitants, with significant disparities depending on the region of residence.

At constant age (standardized rate), regional admission rates are generally higher than the national average in the southern half, with a record for Corsica (41.1). But the Bourgogne-Franche-Comté, Grand Est and Hauts-de-France regions also show rates higher than the national average.

Thus, Bourgogne-Franche-Comté occupies second place with nearly 35 visits to emergency rooms per 100,000 inhabitants, 10 points more than the national average.

Did you think you'd be able to leave the emergency room quickly after coming in for dehydration or heatstroke? Wrong: In the majority of cases (62%), admission to the emergency room is followed by hospitalization.

This is obviously more true among the youngest (62.8% among those under 6) and the oldest (up to 83% of those over 90), but it is quite common among others as well. Thus, more than half of 40-59 year-olds and more than a quarter of 30-39 year-olds who visited the emergency room in connection with the heatwave were hospitalized. It is even nearly a third among 6-19 year-olds.

On the occasion of this new early heatwave, the health authorities are reminding people of the good behaviors to adopt to protect themselves - for the most vulnerable but also for the entire population: drink plenty of water, avoid alcohol, stay in the shade and/or cool as much as possible, especially during the hottest hours of the day, avoid physical activity in conditions that are too hot.