Legionellen in der Trinkwasser-Installation – Die Methode macht den Unterschied

Legionella in drinking water installations – the method makes the difference Introduction: Legionella infections can cause Legionnaires’ disease, a severe form of pneumonia, as well as Pontiac fever. It is transmitted by inhaling aerosols. Water from drinking water installations where the water is heated in a centralised container must therefore be checked regularly for the hygienic and microbiological parameters Legionella spp. under certain circumstances (DVGW W 551). In Germany there is a recommendation from the German Environment Agency (German: Umweltbundesamt – UBA) for the analysis of Legionella in drinking water installations, which evaluates the laboratory results in the sense of a worst-case scenario. Different measures may be necessary when these findings are compared with the results from an internationally standardised statistical approach (DIN EN ISO 8199; DIN EN ISO 11731), leading in turn to differing requirements in terms of reporting and action. Method: In our study the drinking water installations of eight buildings, with known microbial Legionella contamination, were closely examined in terms of time and space for the presence of Legionella spp. Results: Differing assignments for the two compared analysis algorithms in regard to the DVGW evaluation categories were determined for 24 % of the 58 sampling days. Conclusions: The evaluation according to the UBA recommendation focuses on the prevention of high contamination in regard to human health. However, microbiological results generated in this way can be associated with considerable statistical uncertainty and even randomness. Keywords: drinking water installations – legionella – national guidelines