Legionella pneumophila is a pathogen that causes severe pneumonia in humans; L. pneumophila serogroup 1 accounts for at least 90% of infections. This is not linked to an environmental predominance of Legionella pneumophila 1, but may be due to a greater virulence of the strain. L. pneumophila sg 5 has also been reported, albeit less frequently, to be a cause of the disease. We report a case of L. pneumophila sg 5 occurring in a large hospital in southern Italy (Apulia region), where both L. pneumophila sg 1 and sg 5 were detected in the water supply; the nosocomial origin was demonstrated by molecular subtyping (PFGE). An environmental investigation, performed immediately after diagnosis of the case of legionellosis, identified a ow L. pneumophila sg 5 contamination level. Our experience highlights that in hospital, risk assessment, in rder to institute control measures for Legionella, should be carried out not only in response to a case of the disease and/or in risk wards only, as described in the Italian Guidelines, but periodically in every ward. The present study confirms that, although in the community L. pneumophila sg 1 is the most frequent strain isolated in both outbreaks and isolated cases, in hospital other serogroups and species may often cause infection because of the high susceptibility of the hosts.
Legionella spp; legionellosis; bacteriological diagnosis; epidemiology