Nosocomial legionellosis: investigation of an outbreak of two cases and control measures

Clinical case - A nosocomial legionnaire's disease was diagnosed in two pat ients hospitalized in the infectious diseases unit in 1997 and 1998. This u nit was equipped with an air humidifier and hot water was produced in heati ng tanks. Water samples from showers, washbasins, water heating tanks, air humidifiers, and the cooling lower were studied. The patients were infected with Legionella pneumophila serogroup 6 strains with similar typing patter ns under pulsed-field gel electrophoresis (PFGE). The air humidifier, the c ooling towel; and ail the hot water systems were contaminated. in the two p atients' rooms, L. pneumophila was detected in shower water samples up to 1 0(5) colony-forming units/L: the serogroup and PFGE patterns of this isolat e were similar to those isolated in the two patients. Comments - The contamination of the hot water system probably resulted from the water heating tanks of the hospital, which had never be cleaned, and f rom the numerous idead-end tubes'. Replacement of water heating tanks with instantaneous water heaters, heat treatment of the water distribution syste m, preventive chlorination up to 2 mg/L, study and improvement of the water distribution systems made hot water use safer, in 1999, 83% of the water s amples analysed complied with our security guideline (< 50 cfu/L in protect ed areas for highly susceptible patients, < 1000 cfu/L elsewhere). (C) 2000 Editions scientifiques et medicales Elsevier SAS.