Despite an increase of literature data on spp. presence in private water systems, epidemiological reports assert a continuing high incidence of Legionnaires' disease infection in Italy. In this study, we report a survey on spp. colonization in 58 buildings with solar thermal systems for hot water production (TB). In all buildings, spp. presence was enumerated in hot and cold water samples. Microbiological potability standards of cold water were also evaluated. spp. was detected in 40% of the buildings. Moreover, we detected correlations between the count of spp. and the presence of the optimal temperature for the microorganism growth (less than 40 °C). Our results showed that cold water was free from microbiological hazards, but spp., was detected when the mean cold water temperature was 19.1 ± 2.2 °C. This may considered close to the suboptimal value for the growth (more then 20 °C). In conclusion, we observed the presence of a Legionnaires' disease risk and the need of some strategies aimed to reduce it, such as the application of training programs for all the workers involved in water systems maintenance.
