Introduction: Legionellosis represents an increasingly important public health challenge, and its rising incidence is associated with an interplay of environmental, technological, and system-related factors. In addition to the characteristics and management of water systems, contempo-rary risk factors associated with climate change, the energy transition, and changing tempera-ture conditions within water systems are becoming increasingly important. Theoretical background: Higher outdoor temperatures can contribute to the warming of cold water in pre-mise plumbing systems, while measures aimed at reducing energy and water consumption may alter temperature and hydraulic conditions within these systems. Cold-water systems and established colonisation pose a particular challenge, as bacteria of the genus Legionella can persist in biofilms under favourable conditions and proliferate even in cold water. Aim: The aim of this master’s thesis was to examine contemporary risk factors associated with the rising incidence of legionellosis and, in the empirical part, to assess the presence and concentration of Legionella spp. in cold water within premise plumbing systems in relation to weather and tem-perature conditions, particularly during heatwaves and periods of intense rainfall. Methods: A total of 72 cold drinking water samples were collected from seven buildings under different weather and temperature conditions. Weather conditions, cold-water temperature at the time of sampling and after two minutes of flushing, selected physicochemical parameters, and the pre-sence and concentration of Legionella spp. were monitored. The results were analysed in rela-tion to cold-water temperature, weather conditions, and selected characteristics of the buildings and premise plumbing systems. Results: During the two heatwaves, cold-water temperatures at individual sampling points reached or exceeded 25 °C both at the time of sampling and after two minutes of flushing. The presence of Legionella spp. was significantly more frequent at cold-water temperatures ≥ 20 °C, both at the time of sampling (79.2 % vs. 27.1 %; p < 0.001) and after two minutes of flushing (76.9 % vs. 37.3 %; p = 0.013). The results also showed frequent recurrence of positive findings at the same sampling points, highlighting the impor-tance of the prior condition of the premise plumbing system and potential established colonisa-tion. The effects of heatwaves on Legionella spp. concentrations and of intense rainfall on their presence could not be statistically confirmed. Conclusion: The results indicate that cold-water warming is an important factor associated with the presence of Legionella spp., while the prior condition of the water system also plays an important role.
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