Addressing Water Age to Manage Legionella Pneumophila

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      A Minnesota Hospital established a Water Management Program (WMP) aligned with Centers for Medicare and Medicaid Services (CMS) and American National Standards Institute/American Society of Heating, Refrigerating and Air-Conditioning Engineers (ANSI/ASHRAE) Standard 188 with the goal to mitigate the risk of waterborne pathogen disease, namely Legionella pneumophila. Initial culture-based validation testing yielded positive Legionella results at distal locations including patient rooms in the potable water systems. Water quality monitoring confirmed low levels of free residual oxidant (FRO) disinfectant, leading to higher Legionella positives. This lower FRO was identified as a problem caused by high water age, defined by a long period of stagnation of water in the potable systems. To address the water age, the hospital's water management team (WMT) implemented a flushing program as part of ongoing verification and validation protocols.


      Based on industry standards, the WMT focused on achieving a minimal control limit of 0.2 ppm (parts per million) of FRO to reduce water age on hot water systems. The WMT's solution included automated flushing on hot water returns, Environmental Services (EVS) personnel provided manpower for flushing at fixtures in patient areas based on low census and patient discharge. Validation testing confirmed the efficacy of the flushing program to reduce water age which in turn reduced Legionella growth.


      The flushing program was able to increase the average FRO level in the hot water systems < 0.05 ppm (2019) to >0.20 ppm (2021). The higher FRO levels contributed to the downward trend of 17% positive Legionella samples (2019) to 0% (2021) during Validation sampling.


      Reducing water age by involving EVS in the WMT and implementing flushing procedures increased FRO levels system wide. Flushing was the simplest, safest, and most cost-effective solution compared to other solutions like supplemental disinfection while also reducing positive-detect Legionella samples.
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