Legionella: Understanding the Risks and How to Prevent Them
Reported cases continue to highlight the importance of preventive measures and the regular maintenance of water systems.
But what exactly are Legionella, how are they transmitted, and what should be considered, especially during the summer months?
What Are Legionella?
Legionella are bacteria that occur naturally in water. In low concentrations, they generally do not pose a health risk. Problems arise when they multiply extensively in water systems and become airborne in the form of fine water droplets (aerosols).
Why Can Legionella Become More Problematic During Summer?
Summer temperatures create conditions that promote the growth of Legionella.
High outdoor temperatures can warm water installations. Extended periods of absence, such as during holidays, can lead to water stagnation in pipes. When these factors occur together, Legionella find ideal growth conditions, as they multiply particularly well at temperatures between 25°C and 45°C. Their growth decreases significantly at temperatures above 55°C, and they are generally killed rapidly at temperatures exceeding 60°C.
How Is Legionella Transmitted?
Legionella infection is not transmitted by drinking water.
Instead, Legionella are spread through tiny water droplets (aerosols), which can be generated by:
- Showers
- Humidifiers and misting systems, including indoor decorative fountains
- Hot tubs and whirlpools
- Air conditioning systems
- Other technical systems that produce water aerosols, such as vehicle wash facilities
- Cooling towers
When these aerosols are inhaled, Legionella can enter the lungs and cause infection. Transmission from person to person is extremely rare.
What Symptoms Does a Legionella Infection Cause?
Legionnaires’ disease (legionellosis) is a form of bacterial pneumonia.
Typical symptoms include:
- High fever
- Cough
- Shortness of breath
- Muscle and joint pain
- Headache
- General feeling of illness
Older adults, smokers, people with weakened immune systems, and individuals with chronic illnesses are at a particularly high risk of developing severe disease.
How Can the Risk Be Reduced?
The risk of Legionella growth can be significantly reduced with a few simple preventive measures:
- Maintain or periodically heat hot water systems to at least 60°C.
- Regularly flush infrequently used water outlets.
- After extended periods of non-use, allow all taps and showers to run for several minutes before use.
- Perform regular maintenance of water systems.
- If contamination is suspected, carry out a Legionella analysis.
When Is a Legionella Test Recommended?
A Legionella test may be advisable:
- When Legionella contamination is suspected
- After extended building vacancies or operational shutdowns
- When hygiene issues occur in hot water systems
- As part of the routine monitoring of water systems
A professional Legionella analysis can determine whether elevated contamination is present and whether further corrective measures are required.
Our microbiological analyses can determine whether Legionella are present in water samples. If Legionella are detected, we can perform additional specialized analyses to identify the specific Legionella species involved. This information can help trace the source of contamination or identify the origin of an infection.
Conclusion
Cases linked to residential buildings, vehicle wash facilities, and the recent outbreak associated with cooling systems in Basel demonstrate that Legionella can become a risk wherever bacteria are able to multiply in water distribution systems or technical water installations and spread through aerosols.
Effective prevention relies on proper system design, regular maintenance, and, where necessary, microbiological testing of the affected water system.
Further Information
- Swiss Federal Office of Public Health (FOPH): Legionellosis (Legionnaires’ Disease)
https://www.bag.admin.ch/en/legionellose-legionaerskrankheit - Swiss Federal Food Safety and Veterinary Office (FSVO): Shower and Bath Water – Requirements and Hygiene
https://www.blv.admin.ch/en/dusch-und-badewasser
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