A 58-year-old woman dies after contracting Legionnaires' disease: the crucial importance of temperature monitoring
- Jonatan De Winne
- Dec 10, 2025
- 3 min read
Updated: Dec 11, 2025
Several French Belgian media outlets recently reported the death of a 58-year-old woman from Legionnaires' disease contracted after a visit to a wellness center. According to researchers, the hot water circulation system was faulty: an interruption in the flow created conditions conducive to the proliferation of Legionella bacteria. The victim's partner filed a complaint, and the Mons public prosecutor's office issued an appeal for witnesses to identify other victims in Mouscron. Anyone who has contracted Legionnaires' disease in the last five years is asked to come forward to the police station.
This tragic example painfully demonstrates that Legionnaires' disease is a very real problem. Without proper monitoring and follow-up, a potentially fatal danger will arise sooner or later.
Legionella and fever
Bacteria grow most rapidly in water temperatures between approximately 25°C and 50°C and optimally in warm water between 30 and 45°C.
At 50°C, the bacteria die, but it takes 2 hours for 90% of them to be destroyed. At 60°C, this only takes 2 minutes.
In a well-managed hot water system, hot water is stored at a minimum temperature of 60°C, the circulation pipe is at a minimum temperature of 55°C, and this latter temperature reaches the taps within one minute.
Cold water in pipes must remain below 25°C (ideally even 20°C) to prevent any unwanted growth.
When the hot water temperature drops, for example because of a faulty circulation pump, poor maintenance or failure of certain parts of the system, the water can remain for a long time in the "danger zone": neither hot enough to kill bacteria, nor cold enough to inhibit (stop) their growth.
Why "feelings" are not enough — the role of measurements
Relying solely on your perception of water temperature or proper circulation is risky. A temperature drop, for example from 55°C to 46°C, might go unnoticed in the shower, but Legionella bacteria will still be present and have harmful consequences.
This is where the crucial use of monthly temperature measurements becomes truly meaningful:
Monthly checks allow for the early identification of structural temperature drops (for example, due to a faulty circulation pump or hot water backing into the cold water pipe).
You can then take proactive action: check or repair the pump, replace mixer taps, etc.
Documentation is also important to enable tracking of developments over time and the establishment of links.
Contamination can occur invisibly and silently.
The proliferation of Legionella pneumophila (= the most frequent cause of Legionnaires' disease) does not occur suddenly: it multiplies gradually, particularly in biofilms and stagnant or slow-moving water.
This makes Legionnaires' disease doubly dangerous:
On the one hand, there is the invisible nature: we feel nothing, we see nothing, we sense nothing.
On the other hand, there is a latent threat: even minor installation or maintenance defects can, over time, lead to exponential bacterial growth.
That is why it is essential not to rely on the principle "we use the showers every day, so they must be in good condition", but to take and record concrete measures every month.
Monthly temperature measurements: a simple first line of defense
One of the measures we explicitly advocate is the integration of monthly temperature readings as a routine practice, for both hot water taps and cold water systems.
The advantages are obvious:
You detect defects, insufficient flow rates or other anomalies in a timely manner.
This prevents stagnation or risky water temperatures that would allow Legionella to proliferate freely.
You improve the safety of residents or users, and thus save lives.
The tragic death of this 58-year-old woman shows that it can be a matter of life or death.
Conclusion: to measure is to know… and to survive
Legionnaires' disease is a very real threat. The bacteria proliferate silently, often going unnoticed until it is too late. A sanitation system can be perfectly installed and compliant with best practices, but as long as it is not maintained and inspected, the risk remains significant.
By recording your monthly temperature readings, you're taking a simple yet effective step to combat this insidious danger. It's not just about comfort or maintenance; it's a matter of responsibility, safety, and, quite literally, protecting life.
If you have any questions about this, we will be happy to help you identify risk points and implement effective management to minimize the risk of Legionnaires' disease.
