Sequence-based typing of Legionella pneumophila strains isolated from hospital water distribution systems as a complementary element of risk assessment of legionellosis in Poland. 
Many factors affect the risk of Legionella infection, such as the design, construction and maintenance of water distribution systems, the presence of individuals who may be exposed and their vulnerability to infection, and the degree of water system colonization and properties of Legionella strains.  For epidemiological investigations, two properties of the Legionella strains are usually determined: serotyping and genotyping (sequence-based typing, SBT).  In Poland, data regarding legionellosis are fragmentary, despite the fact that this has been a notifiable disease since 2002.  The number of reported cases is very low; moreover, the main method of diagnosis is serological examination (delayed diagnosis and cheaper methods), and only single cases of LD were confirmed by culture of bacteria.  Therefore, after 10 years of mandatory reporting of the Legionella spp.  infection in Poland, the real epidemiological situation is still unknown; however, risk assessment should be carried out, especially in hospitals.  In the presented study, comparison of the sequence types of 111 isolated L. pneumophila strains (from hospital water systems) with those present in the EWGLI SBT data was undertaken for complex risk analysis as a complementary element.  In total, strains of L. pneumophila belonging to 12 out of 19 STs determined in the presented study were previously reported to the EWGLI SBT database (ST1, ST42, ST59, ST81, ST87, ST114, ST152, ST191, ST371, ST421, ST461, ST520).  Among these strains, only 7 STs were previously reported in the amount of ≥10 (mainly ST1, ST42, ST81).  Analysis of EWGLI data were carried out and, proportionally, the highest percentage of hospital-acquired strains (clinical and environmental) was found for ST 81, ST421 and ST152, but the largest number was for ST1.  Based on the EWGLI data and the presented results, it was found that persistent colonization of HWS of 3 hospitals by strains belonging to ST42, ST1, ST87 indicated an increased risk of legionellosis, especially ST42.