Health and climate
Legionellosis, a hidden danger especially in summer
This respiratory disease is progressing. Air conditioning, in particular, is pointed out. Immunodeprime and elders run more risks.
The legionellosis is due to a bacteria present in water and wetlands. A pulmonary infection can occur if a person inhales contaminated droplets. (Illustration photo)
Imago/AAP
- The cases of legionellosis in Switzerland have multiplied by five between 2000 and 2021. A certain stagnation has been observed since, but the experts do not speak of perspective.
- This increase is notably attributed to climate change and the aging of the population.
- Summer, during which we use more and more air conditioners, is a sensitive season.
In January 2025, a High legionelle concentration Was noted in the showers of the college of Chêne, in Aubonne (VD). Although it had already been treated, the bacteria had reappeared during the winter holidays. Students and local companies were then prohibited from using showers.
The phenomenon is not unique. According to a rapport Published on June 10 in the Bulletin of the Federal Office for Public Health (OFSP), the number of cases of legionellosis has not stopped increasing in Switzerland in Switzerland over ten years, also observed in Europe.
What is legionelosis?
The disease was described for the first time in 1976, to people who had attended an American Legion Convention (Association of Veterans), in Philadelphia. This episode, during which 182 people were infected and 29 died, explains his name.
Infection is caused by genre bacteria Legionella. In Europe, it is in 95% to 97% of cases of the Legionella pneumophila. This bacteria multiplies in water, at temperatures between 15 and 50 degrees. She is killed at 60 degrees. Interhuman transmission is extremely rare. The usual transmission is by inhaling suspended water droplets in the air. Swallowing contaminated water is not dangerous.
These bacteria can cause a simple influenza condition, which heals spontaneously after a few days. This is Pontiac fever. The symptoms being light, they do not generate any particular investigations, and are only extremely the subject of an announcement. Legionnaire’s disease describes the pulmonary and more serious form of the disease.
Daniel Mäusezahl, professor at the Tropical Institute and Public Health Swiss (Swiss TPH) and author of this study, specifies that the infections announcements were multiplied by five Between 2000 and 2021, from 140 to 677. Since then, there has been stagnation around 650 cases per year. However, it is not found in other European countries and, as annual variations occur, experts do not speak of perspective.
Legionella in water in Switzerland
The legionellosis is due to a bacteria present in water and wetlands. For example, it can be found in showers and air conditioning, but also in jacuzzis or washing systems. A pulmonary infection can occur if a person inhales contaminated water droplets.
It is estimated that 5% to 10% of patients who develop the most serious form of infection (Legionnaire’s disease, read our recovery) Died, despite the antibiotics. What take things seriously: in 2019, the Confederation created a group of specialists responsible for fighting this pathology.
Gilbert Greub, director of the CHUV microbiology institute.
Willy Blanchard CEMCAV-CHUV
“It is an important disease, with pulmonary infections that can be severe,” confirms Gilbert Greub, director of the CHUV microbiology institute. The effects on health depend in particular on the quantity of bacteria present and the dangerousness of the strain.
Immunocompromised and seniors
Immunode -depressed and elderly people are more at risk. “It seems that in healthy people, the immune system manages most of the time to do its job,” confirms Jacques Schrenzel, doctor responsible for the bacteriology laboratory at HUG and president of the Federal Commission of Experts for Biological Security.
Jacques Schrenzel, doctor responsible for the bacteriology laboratory at the HUG and president of the Federal Commission of Experts for Biological Security.
Yvain Genevay/ Le Matin Sunday
Several factors probably explain the increase in cases. To the rank of which climate change (with warmer periods and the more frequent use of air conditioners), the augmentati0n of the number of elderly or immunocompromised people, better recognition of the disease and better tools to diagnose it.
The study conducted in Switzerland, in which Gilbert Greub and Jacques Schrenzel participated, aimed to collect additional information. “We asked patients about their profile, health, home, lifestyle and the contacts they have with water (to wash your car or swim, for example),” said the first.
The results confirm that there are many potential sources of infection and that the bacteria incriminated are common in our homes, even those where no disease is declared. “At the same time, despite this frequent presence, very few people contract the legionellosis – a paradox which underlines the complexity of the transmission routes,” notes Daniel Mäusezahl.
Practical advice against legionellosis
Gilbert Greub adds that in the event of an epidemic the source can generally be identified. On the other hand, it is difficult to establish for isolated cases and many infections are not recorded because they are considered as banal viral infections.
This shows the importance of performing the right gestures and informing the population. In hospitals, for example, maintenance services are trying to regularly circulate the water distribution system. This can also be treated and devices make it possible to cause regular thermal shocks in the pipes to kill the legionella.
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“For example, professionals who install air conditioning are informed of these risks,” adds Jacques Schrenzel. And individuals must respect the manuals for using such devices. ” A word of advice: it is necessary to wash regularly the machines operating with water, which must also be changed often. And then, after a prolonged absence, the water must be allowed before using it. Finally, immunocompromised people generally receive more precise information from their doctors.
Climate: Beware in summer!
These recommendations are even more in summer, with the increased use of foggers, air conditioners or water fountains. Which, unfortunately, suggests a bright future for legionella. Jacques Schrenzel warns: “With climate change and ever warmer summers, the problem will further increase.”
Daniel Mäusezahl insists on the importance of further expanding the analyzes. The investigation which has just been carried out shows that the shower is not the only culprit. To examine all potential sources, it therefore considers “essential” to permanently compare genetic data from the Legionella discovered among patients with those present in the environment, and calls for the creation of a national database in Switzerland.
“I stayed eight days in a coma”
“When I was told that I had the legionellosis, I was not particularly afraid, because I did not know this disease,” recalls Kess. We were in September 2021, the fifties had just returned from New York. “I was coughing and I was struggling to breathe. My mother forced me to go see the doctor. He discovered that I had severe pneumonia and sent me to the hospital, where the diagnosis was made. ”
A day later, the Friborg is plunged into a coma, under artificial breathing. “I spent eight days there. Doctors thought I was going to die … They did a great job, but coma was a painful experience. I felt locked up in a universe I couldn’t get out. In my dreams, I saw my partner: it was she who pushed me to fight. ”
When he wakes up, Kess can no longer walk. He suffers from a pulmonary embolism and has to spend two additional weeks in the hospital. “When I returned to Brooklyn, where we lived then, I could barely go around the Pâté de Maison. I lacked breath, but also muscles. I finally felt a little better at the end of December 2021. ”
The 50 -year -old thinks he has contracted this disease in the New York metro, after a period of heavy rains. He specifies that in 2021 he had already exceeded 50 years. “Besides age, men are apparently more likely to be infected. And then I am a smoker, which is another risk factor. ”
Since this episode, Kess is no longer quite the same. “I don’t know how much it’s linked, but I have anxiety attacks, like post-traumatic stress. And then I feel a little guilty of having survived. I tell myself that I should enjoy more life, but it doesn’t happen like this. ”
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