How Molecular Typing Can Support Environmental Surveillance in Hot Water Distribution Systems: A Hospital Experience.

In this study, we aimed to associate the molecular typing of isolates with a culture technique during routine hospital environmental surveillance in hot water distribution systems (HWDSs) to develop a risk map able to be used to prevent nosocomial infections and formulate appropriate preventive measures. Hot water samples were cultured according to ISO 11731:2017. The isolates were serotyped using an agglutination test and genotyped by sequence-based typing (SBT) for or macrophage infectivity potentiator () gene sequencing for non- species. The isolates' relationship was phylogenetically analyzed. The distribution and level of contamination were studied in relation to temperature and disinfectant residues. The culture technique detected 62.21% of positive samples, characterized by serogroup 1, non-, or both simultaneously. The SBT assigned two sequence types (STs): ST1, the most prevalent in Italy, and ST104, which had never been isolated before. The gene sequencing detected and . The phylogenetic analysis showed distinct clusters for each species. The distribution of isolates showed significant differences between buildings, with a negative correlation between the measured level of contamination, disinfectant, and temperature. The molecular approach introduced in HWDSs environmental surveillance permits (i) a risk map to be outlined that can help formulate appropriate disinfection strategies and (ii) rapid epidemiological investigations to quickly identify the source of infections.