Legionella monitoring in building’s water distribution systems: the case study of a sparse University campus

This paper investigates the presence of Legionella in the water distribution systems of buildings of the University of Perugia (Italy). Further, as the genus Legionella comprises many different species and serogroups, of which L. pneumophila sg1 is the most often associated to human lung infections, a molecular characterization of the retrieved Legionella isolates is reported.

Legionella was monitored by standard methods analyzing more than 300 water samples collected from 100 taps throughout the university campus. Legionella was absent in the great majority of the samples, while it was found in only five buildings of the entire campus. Molecular analysis indicated that the contaminations were only partially ascribed to L. pneumophila sg1, as other serogroups (sg8 and sg10) as well as other species (L. taurinensis and L. anisa) were also found. Further, in only three cases the levels of contamination were above the limit at which, according to international guidelines, remedial actions are required. In particular, a thermal disinfection, i.e., raising the water temperature above the level at which Legionella cells do not survive, was applied to the hot water supply systems where high temperature could be maintained throughout. On the contrary, in a building in which Legionella contamination originated inside the heat exchanger, a chemical disinfection with silver hydrogen peroxide was carried out.

The case study herein reported indicates how a multidisciplinary approach that integrates microbiological analysis with the survey of building’s plumbing systems can lead to the definition of effective strategies for Legionella prevention and control.