SRF recently published an informative article about Legionella. Here's a summary of the most important information:
Legionella are bacteria that are inhaled via water vapor. These bacteria can cause severe pneumonia. The bacteria thrive in warm, moist environments. Anywhere where large quantities of water vapor are generated is a potential source of Legionella.
The number of Legionnaires' disease cases has increased in Switzerland. The Federal Office of Public Health is coordinating measures with all relevant stakeholders and has established a Legionella task force.