[5-year surveillance for Legionella pneumophila and comparison of disinfection methods in two hospitals of Milan]

Abstract

We performed an environmental monitoring in an hospital to estimate the level of contamination from Legionella spp., in connection with several treatments of reclamation. In period 2002-2006 we executed 238 samplings in 21 units hospitals (from hot water, biofilm, filter of the conditioning system, instrument for the assisted respiration) for the detection of Legionella spp. The contaminated points have been subordinates to reclamation (hyperchlorination, maintenance of boilers/tanks, taps' and showers' substitution, increased temperature, elimination of dead points of the system and chlorine dioxide) and subsequently we sampled to verify the efficiency of the disinfection. Environmental investigation found 58% of the cases positive for Legionella spp. (139/238), with maximum count in order of the 10(4) UFC/L, demonstrating colonization of Legionella pneumophila (132/139, 70% Serogroup 2-14, 19% Serogroup 1, 11% both). The used treatments were effective, in different ways, in the short period, but not in the medium-term, because progressive recolonization happened approximately after a month; only the use of chlorine dioxide brought to counts less than 100 UFC/L until now. Chlorine dioxide seems to maintain a mainly protecting effect, however this effectiveness will have to be demonstrated also for longer periods.