RÉSUMÉ
Although much is known about Legionella and the illness they cause, the relationship between their concentration in water and the risk of infection remains unclear. A comprehensive body of experience shows that the growth of Legionella in heated water distribution systems can be effectively controlled by following the preventive measures described in the generally acknowledged codes of practice. As orientation to trigger action, a technical action level of 100 colony-forming units in 100 ml water has found wide acceptance as the maximally tolerable concentration of Legionella in drinking water hygiene. However, this value as well as the concept for controlling the growth of Legionella in installations has developed historically. In part, the focus differs between drinking water hygiene and hospital hygiene. Also, there is no harmonized European approach for controlling Legionella. In spite of such differences, there are important international parallels in the assessment of the occurrence of Legionella, in experience with controlling them, and in recommendations for prevention. There is a need particularly for adequate studies to clarify the risk of infection as well as for the publication of existing data and experience showing the efficacy of measures for prevention, disinfection and system upgrading. Such data are necessary to support evidence-based prevention of Legionella infections and to create a better epidemiological data base in Germany. One chance for reaching this target would be to improve practices in diagnosis, reporting and central data evaluation-not only of illness, but including also data on Legionella occurrence. More frequent Legionella testing of pneumonia patients is a prerequisite for this, but particularly also for the rapid identification and removal of the source of infection. Further requirements include better training of planers, plumbers, and operators of drinking water installations about the approach to preventing Legionella contamination of drinking water installations described in standards and guidelines. The further development of practicable concepts for effective Legionella prevention requires good collaboration between public authorities responsible for drinking water and hospital hygiene on the federal and state levels and experts for the prevention of infection, hygiene, and sanitary installations.
