Legionellosis: how do you catch it, in water, air conditioning?

[Mis à jour le 5 septembre 2022 à 15h40] The legionellosis is a bacterial disease that causes an acute infection of the lungs, serious and potentially fatal. Adults with risk factors (advanced age, smoking, chronic respiratory diseases, diabetes, immune diseases, immunosuppressive treatments) are more affected. About 1,500 cases of legionellosis are declared in France each year. It is caused by bacteria Legionella pneumophilapresent in fresh water (warm and hot, between 25 and 45°C) as well as in the air conditioning when conditions are favorable. She would probably be involved in the cases of pneumonia observed in Argentina in August 2022, says the provincial health ministry. Where do you catch legionellosis? At the swimming pool ? How to protect yourself from it? Treat her?

Definition: what is legionellosis?

Legionellosis is severe pneumonia (lung disease) which can prove fatal. It is a bacterial infectious disease known since 1976 when it was discovered in fighters of the American Legion gathered in congress in Philadelphia. Legionellosis is also called “legionnaire’s disease”. It’s a disease notifiable which requires rapid and appropriate support.

What is the legionellosis mortality rate in France?

Public health France reports 1,500 cases of legionellosis each year in France, of which 10% death. 3/4 of patients have a risk factor (smoking, obesity, chronic respiratory diseases, etc.).

Where do you catch legionellosis?

Legionellosis is caused by a bacterium called Legionella pneumophila which is present in the natural environment and can proliferate in artificial water sites, when the conditions for its development are met, particularly between 25 and 45°C. There are several species of Legionella, but pneumophila is involved in 90% to 98% of cases. The bacterium in question is hydrophilic, i.e. it lives in aqueous media. Legionella particularly develops:

• in the condensation water of air conditioning systems,
• in lakes, rivers, mud
• in water distribution networks
• in hot water, between 25°C and 45°C, and in stagnant water, especially in swimming pools or on the occasion of showers.
• in the presence of tartarcorrosion of pipes (iron and zinc) and micro-organisms contained in the biofilm.

On the other hand, this disease is not contracted by contact with an infected person, or by drinking water containing legionella.

Can you catch legionellosis from air conditioning?

If poorly or insufficiently maintained, air conditioning and water distribution systems pose a risk of legionellosis. Indeed, stagnant and hot water (between 25 and 45°C) promotes the proliferation of Legionella bacteria.

What temperature to kill Legionella?

Legionella is a bacterium which ceases to multiply below 20°C and above approximately 45°C. They can be destroyed in a few hours at 55°C, in a few minutes at 60°C and instantly at 70°C.

Legionella is not transmissible from person to person.

What is the mode of contamination of Legionella?

Legionella is not transmissible from person to person.. Contamination is mainly through the respiratory route. “Contamination takes place by the environment, by water contaminated by these bacteriaessentially by microdroplets“, explains Dr Pierre Abgueguen, head of the infectious and tropical diseases and internal medicine department at the CHU d’Angers. A patient is therefore not contagious and should not undergo any particular isolation. The only route of contamination demonstrated to date remains inhalation, whether it is the air breathed in an air-conditioned room or the droplets of steam during a hot shower.

What is the incubation period for Legionella?

The incubation period is usually between 2 and 10 daysmore or less asymptomatic phase.

What are the symptoms of legionellosis?

The signs and symptoms that accompany Legionnaires’ disease are similar to those of pneumococcal pneumonia. They can be more or less serious depending on the type of bacteria and the age of the patient. “This fairly rare pneumonia is considered potentially serious and often leads to intensive care”, underlines the specialist. Thus, after the incubation phase, the disease is expressed by:

• Headaches (headaches)
• Muscle and abdominal pain
• Diarrhea,
• A dry cough.
• General fatigue (state of malaise)
• A high fever (up to 41°C).

In a few days, the fever intensifies, the muscular pains are exacerbated while the first respiratory symptoms appear:

• Difficulty breathing.
• A cough with little expectoration.

In the absence of treatment, the disease can quickly degenerate, the symptoms worsening very quickly, until death of the patient, especially in subjects at risk.

What are the risk factors for legionellosis?

• Age: people who are either very young or very old are more likely to develop pneumonia than middle-aged people.
• The gender: men are more affected by the disease than women.
• Smoking.
• Alcoholism.
• Diabetes.
• The chronically illmainly cardiac or respiratory.
• HIV or any other condition that weakens the immune system.
• The pregnancy.

The doctor begins first of all with an interrogation and an auscultation of the patient who will suggest to him a pneumopathy. To confirm this diagnosis, he performs various tests:

• A sputum analysis or fluid collected by bronchial endoscopy.
• An antigenuria: detection of specific Legionella antigen in urine. “Please note, antigenuria only works in serogroup 1 Legionella pneumophila infections (the most common)”qualifies our interlocutor.
• A chest x-ray (which reveals an infectious focus that appears as a white spot).

What treatment in case of legionellosis?

“Given the potential severity of the infection, antibiotic treatment is essential and as early as possible, any delay in treatment that could be detrimental to the patient“, remarks Dr. Abgueguen. If this diagnostic delay is short, treatment with antibiotics or antibiotic therapy is recommended. intravenously, which generally ensures a fairly rapid recovery. Even if the symptoms have disappeared and the patient claims to be better, it is essential to complete the treatment. If the delay is longer, certain vital functions may be in danger, sometimes requiring respiratory assistance for the patient.

• Run cold and hot water at least once a week at water points which are little used (sink, washbasins, shower, etc.);
• Run cold and hot water after each period of prolonged absence, for all water points before reusing them (in particular the shower);
• Monitor the temperature of hot water in the home: it must be very hot but not “boiling” (at least 50°C and at most 60°C at the kitchen sink);
• Regularly descale and disinfect tap fittings (flow aerators, shower heads, etc.);
• Use sterile water for biomedical devices (cleaning and filling oxygen therapy or sleep apnea devices).
• Regularly maintain and/or disinfect air conditioning installations, drinking water distribution installations, cooling towers

Thanks to Dr Pierre Abgueguen, head of the infectious and tropical diseases and internal medicine department at the CHU d’Angers.