Recent Legionnaires’ disease outbreaks in Canada and France provide a valuable reminder that Legionella risks are not confined to traditional high-risk assets such as cooling towers. While the outbreak in Aylmer, Quebec, was ultimately traced to a contaminated school cooling tower, investigations in Savoie, France, identified a restaurant misting system as the most likely source of a significant number of infections. Together, these incidents highlight the need to manage not only recognised risk systems, but also less obvious aerosol-generating devices that may fall outside routine inspection programmes.
In Aylmer, public health authorities investigated an unusual cluster of 17 confirmed Legionnaires’ disease cases. Several people required hospital treatment, although no fatalities were reported. Extensive environmental sampling eventually identified a cooling tower as the likely source, which was subsequently disinfected.
By contrast, the Savoie outbreak challenged many traditional assumptions about Legionella exposure. Between June and August 2026, health authorities recorded 48 cases and two deaths. Investigations found that 30 of those affected had visited the same restaurant in Chambéry, leading authorities to identify a food-display misting system used to cool buffet items as the most probable source. Notably, no further cases linked to the establishment were reported after the system was shut down.
While these outbreaks involved very different systems, they shared a common factor: both generated fine water aerosols capable of being inhaled by members of the public.
Cooling towers and hot water systems are typically subject to robust management because they are well-recognised sources of Legionella. However, incidents such as Savoie demonstrate that smaller, less regulated systems can present similar risks if aerosol generation is combined with inadequate maintenance or controls.
Investigations are increasingly examining a wider range of potential sources, including:
- Decorative fountains;
- Misting and humidification systems;
- Spa pools and wellness facilities;
- Irrigation and water features;
- Food-display misters; and
- Commercial humidifiers.
Many of these assets are not routinely included within formal Legionella management plans, despite their ability to generate respirable aerosols.
The Aylmer and Savoie outbreaks demonstrate that understanding exposure pathways is just as important as controlling recognised Legionella risk systems.
Organisations should consider:
- Reviewing whether all aerosol-generating devices are included within Legionella risk assessments;
- Making sure that non-traditional systems such as misters, humidifiers and decorative water features are appropriately maintained and inspected;
- Verifying that management plans focus on actual exposure risk, not solely asset categories;
- Maintaining robust records to support rapid investigation if cases arise; and
- Periodically reassessing whether system changes, operational practices or warmer climatic conditions have introduced new risks.
The contrasting outbreaks in Aylmer and Savoie demonstrate that Legionella does not discriminate between a large cooling tower and a seemingly innocuous misting system. The common denominator is aerosolised water and human exposure.
While compliance remains essential, effective water safety management requires organisations to challenge assumptions, identify emerging risks and make sure that all potential exposure pathways are understood and controlled.
In many cases, the next significant risk may come not from a known hazard, but from a source that was never considered one. If you need any support with your Legionella management, please get in touch.