Rush on Mist Coolers during the Heat Wave: How to mitigate Legionella risk?

Fans, air conditioners, mist coolers, swimming pools and fountains … With a temperature averaging 40°C in most of Europe, all means are being used to stay cool. Emergency plans have been activated in many regions and shops are running out of cooling equipment.

By teamblog

Jan 14, 2020

Municipalities took steps with heat to limit effects of record temperatures

Just like in Poissy, a Parisian suburb, mist showers have been set up by various cities to relieve inhabitants from intense heat. In Paris, the opening hours of some pools were extended to make swimming accessible to the greatest number, sometimes until 10.30 p.m. In addition, sprinklers have been installed throughout the capital and parks and public gardens are open 24 hours a day. The vigilance system for identifying elderly people or at risk and systematically monitoring their health has been activated and water is distributed to the homeless along with maps showing the location of drinking fountains throughout the city.

Regulations on misting machines have become increasingly stricter

In most Western countries, mist machines have to comply with strict installation and maintenance rules. Like any aerosol spraying device, they have to be tested for legionella. In France[1] , regulatory water analyses must be performed every two years. If the concentration of L. pneumophila exceeds 1 000 CFU / L, the operator must stop the system immediately. Corrective actions must be applied and the facility has to be tested again. Return to service is only allowed if the concentration is less than 10 CFU/L.[2]

Rising temperatures promote Legionella proliferation

When a heat wave strikes, even cold water networks can exceed 25°C and become a potential source of Legionella. In addition, cooling devices are being overused during hot weather, which means that in case of water contamination, the risk of infection will be increased.

In swimming pools, extreme attendance during summer results in germs and organic matter accumulating, which tends to neutralize chlorine. Constant agitation of the water also causes its partial evaporation. For these reasons, crowded swimming pools provide an ideal environment to various bacteria, including Legionella.

Attention needs to be reinforced for older people

WHO estimates that people over 50 years old account for 75-80% of all reported cases of Legionnaires’ disease (or legionellosis). This means that older people are more likely to develop the condition, even under normal circumstances. They face an additional physical challenge during heat waves. Their hydration levels must be monitored closely and they must be given easy access to cooling devices such as humidifiers, atomizers, showers and air conditioners. However, despite being useful, this aerosol-generating equipment pose a non-negligible legionella threat. As a result, rising use rates of at-risk cooling devices by the elderly increase their exposition to legionella, leading to an even greater susceptibility to the disease.

How to mitigate legionella risk during hot weather?

In addition to mandatory tests, it is recommended to carry out self-checks on water networks at least once a month. In summer, temperature in cold water systems can reach above 20°C, therefore these must also be tested. Health facilities and nursing homes are particularly affected by non-serogroup 1 Legionella so it is necessary to use test kits enabling detection of all serogroups of L. pneumophila.

Sources :

[1] Code de la santé publique, articles L.1335-3, L.1335-4, L.1335-5 et L.1337-10 du code de la santé publique ; décret du 27 avril 2017 relatif à la prévention des risques liés aux systèmes collectifs de brumisation d’eau ; arrêté du 7 août 2017 relatif aux règles techniques et procédurales visant à la sécurité sanitaire des systèmes collectifs de brumisation d’eau, pris en application des dispositions de l’article R. 1335-20 du code de la santé publique.

[2] Code pénal, Article 226, Légifrance, mai 2011,

[3] Discours Vie Publique, Interview de Mme Agnès Buzyn, ministre des solidarités et de la santé à Europe 1 le 8 août 2018, sur la fin de l’épisode caniculaire et la protection des personnes âgées dépendantes, 8 août 2018,

France 3 Régions, Canicule : les EHPAD et les maisons de retraite vont affronter les fortes chaleurs en Paca, 24 juin 2019,

Helbig, J., Bernander, S., Castellani Pastoris, M. et al., Pan-European Study on Culture-Proven Legionnaires‘ Disease: Distribution of Legionella pneumophila Serogroups and Monoclonal SubgroupsEur J Clin Microbiol Infect Dis (2002) 21: 710., accédé le 20 juin 2019

La Nouvelle République, Canicule : piscine gratuite pour les plus de 50 ans, 24 juin 2019,

Le Parisien, Yvelines : des idées pour se rafraîchir, 23 juin 2019,

Ministère des Solidarités et de la Santé, SYSTEMES COLLECTIFS DE BRUMISATION D’EAU, Prévention de la légionellose : obligations et bonnes pratiques à mettre en œuvre, janvier 2018,

Organisation Mondiale de la Santé, Legionellosis,, 16 février 2018

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