Major articlePrevalence and distribution of Legionella spp in potable water systems in Germany, risk factors associated with contamination, and effectiveness of thermal disinfection

- Potable water systems in households and public buildings are colonized by Legionella spp. in up to one third of buildings, most commonly by L. pneumophila.
- The degree of contamination with Legionella spp. can vary widely between different faucets in the same building. Single faucets can be permanently contaminated even if the central supply is mostly free of Legionella spp. due to the design of faucets, differences in user behavior and biofilm formation.
- In many buildings, there is little information about the extent of the hot water system and the condition of the pipes. Maintenance is often restricted to the central system, while the hydraulic conditions are unknown or not under control, leading to insufficient temperature and stagnation in parts of the peripheral system with an increased risk of Legionella spp. colonization.
- Effectiveness of thermal disinfection to remove Legionella spp. colonization from a hot water system is limited and may be insufficient if concentrations are high.

BackgroundWorldwide, Legionella spp are a common cause of community-acquired pneumonia. Potable water systems are a main reservoir; however, exposure in the community is unknown.MethodsWater samples from 718 buildings in Germany were collected. Possible risk factors were prospectively recorded. All samples were tested for Legionella spp using cultural microbiologic methods. Samples were assigned to 1 of 5 levels of contamination. Statistical analysis was performed to determine the influence of risk factors for contamination and, in a subgroup of buildings, for unsuccessful thermal disinfection.ResultsIn total, 4,482 water samples from 718 different water supply systems were analyzed. In 233 buildings (32.7%), Legionella spp were identified, 148 (63.5%) of which had a medium or higher level of contamination. The most common species was Legionella pneumophila (94%). Contamination was strongly associated with temperature in the circulation, but not with the size of the building, time of the year, or transport time to the laboratory. Thermal disinfection was successful in fewer than half of the buildings.ConclusionsThere is relevant exposure to Legionella spp in the community. Water systems are not always up to current technical standards. Although microbiological risk assessment remains a challenge, there is a case for monitoring for Legionella spp outside of hospitals.