Surveillance of Legionella Waterline Colonization in 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 water colonization was performed to evaluate the system weakness and to implement environmental preventive measures. METHODS: Three repeated campaigns of water sampling were performed in different seasons from February 2004 to June 2006. Overall, 66 water samples were collected: 52 in wards with at-risk patients from 3 buildings (two old (A-B) and one new (C)); other 14 samples from boilers. The samples were analysed, following national legionella standard methods; water temperature, pH and residual free chlorine were determined at the time of collection. RESULTS: A total of 8 samples (12.1%) resulted positive for Legionella spp. In hospital wards 6 (11.5%) samples were positive and the isolates were L. gormanii (1) and L. pneumophila (5). The highest colonization rate was observed in building C (26.7%), vs 5.5% in B and 5.3% in A. 14.3% samples from boilers were also colonized by L. pneumophila. The percentage of positive samples was: 6.7% in autumn-winter and 23.8% in spring-summar campaigns. The average temperature was lower in colonized samples (39.1° vs 46.5°). In 71.4% of samples the level of L. pneumophila contamination was beween 103 and 104 CFU/L. CONCLUSION: Hospital water system seams to be affected by Legionella colonization most frequently in spring-summar and in the new buildings (C). It is necessary now to investigate on the temperature level mantained in hot-water system and also to observe if the structural characteristics of water ducts of C-building can influence the colonization observed.