Background: Better understanding of Legionella colonization patterns is necessary to manage water systems more efficiently. Our objective was to determine if colonization rates differed in hot vs. cold water, or at certain sites within the hospital.
Methods: Environmental samples collected between 3/07 and 12/14 at VA Pittsburgh were analyzed. Hot water swabs and samples were collected from 2007-14. Cold water samples were also collected from 2013-14. Legionella isolated on culture were identified as blue-white fluorescing species (BW), Lp 1 or Lp 2-14. Chi-square and logistic regression modeling tested associations between culture results and other factors.
Results: Overall, 5.5% (178/3,230) of environmental samples were positive for a Legionella sp. (Lp1, n=96; BW, 68; Lp2-14, 6; mixed spp., 8). From 2007-14, Legionella positivity rates differed by site: Building 1= 6.6%, 6= 10.9%, 29= 2.9%, 30= 0%, 33= 0% (p<0.001). Legionella positivity rates for hot and cold water in 2013-14 (when both were sampled) were 2.5% and 3.8%, respectively (p=0.027). Water samples during this period were more sensitive than swabs (p<0.001). Positive cold water cultures were more likely to yield BW (86%, p<0.001); positive hot water samples were more likely to yield Lp1 (60%, p<0.001). Lp1 were more likely to be recovered from specific building sites, and in particular years (both p<0.001). By adjusted regression modeling, type of sample and year were significantly associated with positive cultures; hot water was associated with Lp1 positivity (all p<0.05).
Conclusion: Legionella species are recovered more often from cold water samples than hot water, an observation that runs counter to conventional teaching. However, Lp1 (the dominant human pathogen) is significantly more likely to be recovered from hot water, and at particular sites within the water system. Cold water Lp1 were evenly distributed across buildings, suggesting transient positivity associated with external water system colonization. The data suggest that hot water surveillance is necessary to detect system hot spots in need of remediation. Cold water surveillance may be useful for identifying water systems that are vulnerable to Legionella colonization through detection of less pathogenic species.
J. Mikolic, None
A. Sonel, None
C. Clancy, None
B. K. Decker, None