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Legionella: are Cadillac prevention efforts still missing the mark?

On November 13, 2019 Johns Hopkins Hospital (JHH) announced that an inpatient was diagnosed with a potentially deadly illness associated with their water system. Water samples collected from the inpatient area reportedly were negative for Legionella known to have infected the patient. If JHH has a state-of-the-art water treatment plan and system, why are they continuing to see cases of Legionella?

Brief background: Published information notes Johns Hopkins Hospital (JHH) has a highly advanced and comprehensive water treatment program targeted at preventing legionella growth within the facility’s water system. They currently use Chlorine dioxide (ClO2) as a disinfectant which has been used on incoming municipal water systems for many years. Available research suggests it is effective at killing Legionella.

According to published reports, the water treatment system installed at JHH was state of the art. It includes  some semi-instantaneous hot water heaters which reduces the amount of stagnant warm water in the system.  We know that stagnant warm water creates an ideal environment for Legionella to grow, making traditional hot water heater tanks a major source of Legionella exposure. The installation of this system strategy, including the ClO2 injection, occurred in 2000. A risk assessment was done where the piping in the facility was reportedly extensively investigated to find and eliminate dead legs in the plumbing that could harbor Legionella. JHH spent significant time and monetary resources on ensuring their facility had a top-notch water treatment system designed to handle any Legionella that could contaminate the system from the incoming water. Yet, despite these exemplary efforts, why did JHH just report a case of illness associated with Legionella?

This is a question that we are commonly hearing. More and more cities and states are enacting legislation targeting the control of Legionella by creating more comprehensive regulations aimed at Cooling Towers and Hospitals, presumably two of the most common sources of Legionella. Why than are we still seeing the number of cases increasing when they should be trending downward? Are the water treatment systems being mismanaged? Are they simply too difficult to manage? Are we seeing more Legionella in municipal water? Are we simply better at diagnosing and monitoring for Legionellosis? Are the current prevention and control strategies by public health official simply wrong? Remember, the current approach to public health strategies are informed by outbreaks, which account for only 4% of all cases. Are we biased or incorrect in our approach because of associated constricted (outbreak) information we incorporate into the strategy? These are all questions that need to be answered. In the meantime, we will be closely following this case, and similar ones, because obviously, somewhere, there is a missing link.

For more information about Legionella and how to reduce risk, contact the experts at Cogency at

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