mycobacteria risks from water and ice machines 797
figure 3. Drinking water and ice machine (DWIM) 2 water and ice. Heterotrophic plate counts (HPCs; CFU/mL) and effects from interventions.
with a 0.15-µm filter and silver-impregnated internal compo- nents. However, a very significant reduction remained in the mean log-CFU of first-drop and 30-second water pre- and postinstallation of the UV/ozone devices in the DWIMs. For machine 2, a significant sustained reduction in the first-
first-drop and 30-second water using a combination of 0.005-µm filter plus UV/ozone disinfection. HPCs of first- drop and 30-second water were consistently below goal levels; however, ice never met goal levels. This machine had silver- impregnated components, and the flushing procedure was not performed. First-drop water met acceptable HPC levels with the 0.005-µm filter alone. When combined with UV/ozone disinfection, the first-drop water had a much lower HPC, which approached the HPC levels of the 30-second water. Machine 4 was not fitted with UV/ozone disinfection
drop and 30-second water to below goal levels when the means of the pre- and postinstallation samples of the 0.005-µm filter plus programmed automatic intermittent flushing were compared. A significant change in the ice HPC was also noted after the 0.005-µm filter plus flushing intervention, but this effect was not sustained. Machine 3 showed the most marked reduction in HPCs in
devices, and the 0.005-µm filter alone did reduce first-drop and 30-second water HPCs to levels consistently below the
goal. Silver-impregnated components did have some effect, but it was confounded by the effect of the 0.005-µm filter. For all machines, UV/ozone disinfection as a single inter-
beneficial, but alone it was not powerful enough to bring water HPCs to goal levels. Cleaning the machines had a somewhat limited short-term effect. Temporary dips were seen in the ice HPCs, but they quickly rebounded. All of the interventions, alone or in combination, were unable to achieve ice HPCs consistently below goal levels.
discussion
Infection prevention specifications for plumbing are often not considered during design and construction of hospitals. We were surprised by the difficulty in maintaining microbial control in the new hospital plumbing system. During our
vention had the strongest effect on HPCs, even compared with the 0.005-µm filter alone. The 0.005-µm filter alone had a significant effect on HPCs, but not as powerful as UV/ozone disinfection. The combination of the 0.005-µm filter plus UV/ozone disinfection was very effective in reducing HPCs in both first-drop and 30-second water to levels consistently below the goal. Silver impregnating of DWIM components appeared to be
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