Legionella e Pseudomonas spp, i maggiori determinanti di infezioni di origine idrica in ospedale: differenze nella contaminazione e nella risposta ai sistemi di disinfezione

In this study, long-term surveillance of Legionella and Pseudomonas spp contamination in water systems of a big hospital and effi cacy of disinfection treatments are reported. In the period 2008-2011, 550 hot water samples from technical rooms and showers/taps of hospital wards were collected for Legionella and Pseudomonas spp isolation by cultural methods. In the hospital, several measures to control water contamination, including shock treatments and continuous systems (chlorine dioxide, monochloramine, boiler) have been employed. Legionella spp was detected in 38.9% of the samples, and the more effective methods in reducing contamination were in order boiler, monochloramine and chlorine dioxide. Pseudomonas spp was isolated in 25.4% of the samples, mainly at peripheral sites; the number of positive sites were reduced effi ciently by boiler, while the other methods did not signifi cantly modify the contamination. Different associations between the two studied bacteria and some water parameters, such as total bacterial count, pH and metals, were observed. Our study points out that Legionella and Pseudomonas spp differ for contamination mode and for response to disinfection systems. The prevalent contamination of pseudomonas at point-of-use suggests that, besides disinfection, the constant maintenance and replacement of faucets and showers is mandatory to control this germ.