Managing Legionella Risk During the Winter Months

Contrary to what many individuals might believe, bacteria can thrive in both extreme hot and extreme cold. Though many strains such as Legionella—the prevalent bug behind a serious type of lung infection (pneumonia) known as Legionnaires’ disease—tend to thrive in warm, wet conditions. In fact, ideal temperature conditions for Legionella tend to range between 25–45°C (77 -113°F).

Given that, it would seem like the risk from these bacteria is just a summertime worry. Unfortunately, that’s not the case. The fact is, warm water conditions can clearly persist during the winter season as well. As such, it’s important for facility managers or those responsible for water-based systems at offices, factories and other commercial or residential buildings to remain vigilant against the risk of a Legionella outbreak even when the days grow short, and the weather turns cold.

Cooling Towers May Not Be Seasonally Dependent

Cooling towers are often associated with air-conditioning condensers, which is more typically a warm weather operation. But in many other use cases, cooling towers are used to cool water temperatures heated by industrial or other commercial processes tied to, say, manufacturing or data centers which must dissipate a large amount of server-generated heat. This latter use case is less likely to be as seasonally dependent and, as such, should be considered an ongoing area for Legionella testing, risk evaluation and outbreak management even during the winter months.

Here are some examples where cooling towers may be more directly associated with air conditioning and warmer-weather use cases:

  • Hospitals
  • Hotels
  • Schools
  • Places of worship
  • Sports facilities
  • Multi-story office buildings

On the other hand, here are some commercial and industrial processes that could have cooling towers, which are less seasonally dependent:

  • Data centers
  • Tool and die manufacturers
  • Cold storage facilities
  • Plastics injection molding and chemical manufacturers

For facility managers in charge of any water systems, including the cooling tower examples above, it's important to have the right process in place to protect against a Legionella outbreak. These general guidelines include:

  1. Knowing Your Systems. Identification of all water-based facility locations, including cooling towers, that might be at risk for a Legionella outbreak.
  2. Setting Limits. Developing protocols that establish critical limits for Legionella that, when crossed, will trigger corrective action.
  3. Tracking Methodology and Ownership. Monitor and evaluate which systems are checked, how frequently, and who is responsible for doing so.
  4. Test! Use a rapid, reliable testing system such as rqmicro.COUNT to measure the prevalence and/or quantities of Legionella bacteria within the water system.
  5. Act! Taking corrective action procedures for those moments when critical limits are met or exceeded.
  6. Establish Record Keeping. Develop a tracking system to report and mitigate risks both for the immediate term and the future. 

Hot Tub Risk for Legionella

During the cold winter months, hot tubs can be a popular indoor reprieve. Unfortunately, the same warm water and jet-action that provides relaxation for people are also ideally suited for Legionella growth and distribution. More so, the efficacy of disinfectants can be reduced with heated water. 

As such, it's important for facility managers or those charged with hot tub management to take certain precautions to mitigate the risk of a Legionella outbreak to protect workers, hot tub users and bystanders alike. Some of these steps can include:

  • Maintaining a proper disinfectant residual and water pH balance. 
  • Having easy access to all components for routine/preventive maintenance.
  • Making sure the basin can be easily and completely drained/refilled. It should also be suitable for regular scrubbing and cleaning.
  • Ideally, locating indoor hot tubs in rooms with isolated air systems and/or dehumidifiers.

Safely Operating Hot Tubs

Use a water management system to establish, track, and improve operation and maintenance activities and keep the following guidelines in mind:

  • All hot tubs have potential for Legionella without proper control measures.
  • Monitor and maintain disinfectant and pH levels-even when the tub is not being used.
  • Follow all manufacturer guidelines for cleaning and all other maintenance.
  • Monitor and maintain a chlorine (3–10 ppm) or bromine (4–8 ppm) disinfectant levels.
  • Test disinfectant residual and pH at least twice per day, or more during heavy use.
  • Backwash sand and diatomaceous earth filters routinely per manufacturer recommendations.
  • Replace cartridge filters on a regular basis per manufacturer recommendations.
  • Ensure water flows across the filter 24 hours/day.
  • Show maximum bather load (CDC’s MAHC recommends 10 per bather).
  • Carry out disinfection with a higher-than-normal disinfectant residual at least once per day
  • Drain, scrub, clean, and fill hot tubs
  • Ensure all staff dealing with hot tub operation/maintenance are properly trained
  • Maintain records for hot tubs and review trends of disinfectant residuals, pH, and maintenance activities.
  • Test for Legionella in accordance using a fast, accurate, and reliable test such as rqmicro.COUNT



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