Persistent colonization of 2 hospital water supplies by L. pneumophila strains through 7 years--sequence-based typing and serotyping as useful tools for a complex risk analysis.

Contamination with Legionella spp. of hot water system (HWS) in hospitals is a considerable problem and elimination of bacteria poses difficulties. Obligatory control of Legionella spp. in hospital HWS was implemented in Poland in 2008y. After that, Legionella spp. has been isolated repeatedly from HWS of the majority of hospitals. The aim of our study was to confirm the permanent colonization with Legionella spp. of 2 hospital HWSs based on the antigenic (serogroup/subgroups) and genetic properties (SBT, rtxA) of L.pneumophila strains isolated in 2004-2011. The dynamic of L.pneumophila population was also examined due to methods of disinfections applied during 7 years. Totally, 134 environmental samples were collected from two hospitals in 2004-2011 (118 from HWSs). During the study disinfection by chlorine dioxide was implemented in both hospitals, while thermal shock was added in the hospital A. Isolated L.pneumophila were serogrouped (105 strains) using Dresden MAb Panel, genotyped by sequence based typing (53) and by harboring of rtxA gene (58 isolates). Legionella spp. were still presented in both systems after 7 years. Exactly the same strains (ST1, ST87, ST114, ST992) were found in the hospital B. While changes of L.pneumophila population were observed in the hospital A: strains still occurred after 7 years (ST835 Sg6, ST114 Sg6); modified antigenic properties (ST835 - Sg12 vs. Sg6); eliminated or maybe not detected (ST81, ST838, ST959). Moreover, the majority of examined strains ST1 (Sg1, OLDA) harboured rtxA gene (hospital B). Our results and data in the EWGLI SBT base indicated higher risk of Legionella infection in the hospital B than A--because of heavy colonization with L.pneumophila ST1. The risk assessment of Legionella infection based only on technical parameters, extent of colonization/contamination level may be not completed. It should be supplemented with the additional examination: serotyping, genotyping and virulence testing of isolated strains.