Time trend of Legionella colonization in the waterline of a hospital of Rome, Italy

Background: In many hospital’s Legionella outbreaks, hot water systems are the most frequent source of infection. Objectives: Considering the old age of the hospital waterline, an investigation on Legionella spp. water colonization was performed to evaluate the system weakness and to implement environmental preventive measures. Methods: From 2004 to 2010, a total of 5 sampling campaigns were performed, collecting 99 water samples from 13 wards and 3 other points of the water line (boilers, point of connection with public water line, hospital waterworks). The samples were analyzed, following national Legionella spp. standard methods. Results: A total of 28 samples (28.3%) were positive for Legionella spp. There has been an increasing time trend until 2008, from 4.5% to 75% in 2008; in the first month of 2010 only 26.3% of the samples were positive. The boiler was positive in 45.5% of samples collected since 2006. In total, surgeries were positive in 38% of cases (8/21): 100% of positive samples in 2006 and 2008, reduced at 50% in the first month of 2010. Only in these wards Legionella spp. were found four times to be >10,000 cfu/L. Among other wards, emergency medicine and oncology are the most contaminated (31% of positive samples). The worst year was 2008 with 75% of positive samples. Conclusion: Hospital water system seems to be affected by Legionella spp. colonization most frequently from 2006 to 2010. The high percentage of positivity in 2008 was related to the presence of a building yard in the hospital. In 2010 there was an improvement, although boilers, surgery, medicine and oncology are still contaminated. It is necessary now to investigate the temperature level mantained in hot-water system and also to observe if the structural characteristics of water ducts could have influenced the colonization observed.