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BackgroundWorldwide, L. pneumophila sg 1 is the most common agent of Legionnaires’ disease ( 80 to 90% of the reported cases). In contrast, L. pneumophila sg 2–14 account for only 15 to 20% of community-acquired cases, although they account for over 50% of the environmental isolates. The discrepancy between environmental isolates and clinical cases of disease suggested that there are differences in virulence.We decided to subtype the environmental Legionella strains isolated from health care facilities (HCFs) and to compare the distribution of strains with the occurrence of hospital-acquired legionellosis.MethodsObservational ecological study based on the data provided by the regional surveillance of legionellosis and on data obtained from hospitals environmental monitoring.Using the monoclonal antibody MAb 3/1 of the Dresden Panel we collected and typed environmental strains of L. pneumophila sg 1 obtained during routine testing in 56 health care facilities from 2004 to 2009.The results of the laboratory analyses of the environmental samples were compared with the number of cases that each health care facility reported during the study period.ResultsThe association between the type of colonisation (L. pneumophila sg 1 vs others serogroups) and the incidence of reported cases was statistically significant (p = 0.03 according to the χ2 test).Legionella strains with the virulence–associated epitope recognised by MAb 3/1 were isolated in 8 of the 26 HCFs colonised by L. pneumophila sg 1; 7 of the HCFs colonised by MAb 3/1-positive strains accounted for 85% of the cases of hospital-acquired legionellosis reported during the 6-year study period. There was a statistically significant association (p = 0.003) between the presence of cases and colonisation by MAb 3/1-positive Legionella strains.ConclusionThis study suggests that hospitals colonised by more virulent strains should be aware of the increased risk and consider the opportunities of increase their monitoring efforts and implement more effective contamination control strategies.

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The purpose of this study was to investigate the distribution of L. pneumophila sg 1 sequence types within the water supplies of 56 healthcare facilities (HCFs) in the Piemonte region.Using Sequence-Based Typing (SBT) we typed 22 environmental strains of L. pneumophila sg 1 obtained during routine testing from 2004 to 2009.Thirty-three percent of the STs obtained from our analysis were unique to the EWGLI database.Of the 22 analysed environmental strains, 11 STs were found in man-made water systems that were associated with human disease. Four STs, which in our study belonged to strains isolated in hospital with reported clinical cases, were already known in the literature. The presence of these STs was confirmed by reports of clinical and nosocomial cases (single cases or clusters), especially for ST 1, ST 23, and ST 42, the most frequently and widely distributed STs worldwide This is the first report in Italy where environmental strains of L. pneumophila isolated from a large geographical area have been identified using SBT. This study confirms that the circulation of some 3 STs is correlated with the development of cluster epidemics in the community or even isolated cases of nosocomial origin. Better identification of the strains which cause the majority of disease would allow for more targeted intervention measures.