Introduction: Bacteria of the genus Legionella are the disease agent of the Legionnaires' disease and the Pontiac fever. The risk for the infection is everywhere where the aerosols emerge. An increased number of bacteria emerges in the internal environment of buildings (water distribution system, ventilation devices, swimming pools, etc.) where the temperature of the water in the system is between 20 and 50 °C. A dead leg is an expression for water pipes that are not or are rarely in use and for the parts of water pipes which became non-flow pipes because of the renovation. Purpose: We wished to ascertain the intensity of bacterial growth of the genus Legionella in dead legs and the positions with less water flow. Methods: In the research, we produced a system by which we simulated the working of the water distribution system in the building. Three different dead legs were built in the system. We performed preliminary experiments and, thus, we checked the reproduction of the Legionella pneumophila bacteria in different media. We used the selected media for further research by which we filled a simulator of the water distribution system. We checked the intensity of the bacteria reproduction in the system and dead legs after 24 hours, 72 hours, and 120 hours of the working of the system. Results: After 24 hours of incubation in the simulator of the water distribution system, the number of bacteria was the smallest in the dead leg 3 (3.656 log CFU ml-1). In the system where water was circulating and in the remaining dead legs, the number of bacteria was approximately the same (approximately 4.5 log CFU ml-1). After 72 hours of incubation, the highest number of bacteria was in the system where water was circulating (6.523 log CFU ml-1). In the dead leg 3, there was the smallest number of bacteria (6.131 log CFU ml-1). After 120 hours of incubation, the smallest number of bacteria was in the dead leg 3 (3.970 log CFU ml-1) and the highest was in the dead leg 2 (4.464 log CFU ml-1). Discussion and conclusion: We ascertained that the bacteria Legionella were reproducing intensively in the entire water distribution system, least in the dead leg 3. Our results showed minimal differences in the number of bacteria regardless of the shape and length of a dead leg. A dead leg does not influence the intensity of the reproduction of the bacteria in the water distribution system. It would make sense to continue the research in a sense to prolong the time of exposure of the bacteria in the water distribution system. We assume that only after more time of exposure, differences in the reproduction of the Legionella bacteria, which are in the water distribution system and in dead legs, could emerge.
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