Legionella Update – How Would You Handle an Outbreak?

Posted by David Burroughs on Aug 19, 2015 2:20:00 PM

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Back in June, QualiChem had a blog post on the approval of AHSRAE 188 which covered Legionella Risk Management Standards for the industry. With the recent legionella outbreaks in New York City and the fact that there generally are an increase in positive Legionella tests during the summer, we wanted to use this blog article to briefly discuss potential measures to take in response to a positive test in your cooling systems as well as share what the City of New York is doing in response to these outbreaks. 

Develop A Water Treatment Program

There have been many different “Best Practice” documents developed in the past by organizations such as CTI and AWT, and also from various water treatment companies on how to respond to a positive test. The most recent standard from ASHRAE lays out a complete plan on how to develop a Water Management Program for legionella. Overall, the general approach by all of these organizations on how to respond to a positive Legionella test has been fairly consistent. The system should be treated with high levels of oxidizing biocides to kill the bacteria and bring things under control, followed by retesting. 

What Constitutes A Legionella Outbreak?

One area that is not as consistent, is what constitutes an outbreak or a trigger point for action.  Is it any test result greater than 0 cfu/ml (colony forming units per milliliter), greater than 10 cfu/ml, greater than 100 cfu/ml, etc? It appears to be generally regarded that a low level positive test result may require only sanitation of the cooling tower system, with a very high result requiring much more extensive sanitation or full disinfection of the tower and other measures to protect the general public and workers from exposure.

On a very general level, there are varying degrees of action to be taken depending on the concentration of legionella bacteria counts measured as noted below, specific actions needed may vary by cooling system and the needs of the facility. Industry sources such as ASHRAE, AWT and CTI should be consulted as well as any other industry experts that may be involved with your situation. The table below presents some typical numbers quoted by industry sources for varying levels of positive legionella tests and how to react.

Measured Legionella CountAction To Be Taken
< 10 cfu/ml Increase biocide additions and maintain monitoring. Retest on your normal schedule
 > 10 cfu/ml but < 1,000 cfu/ml Review program, Increase biocide additions and residual, retest and retreat until back in control
 > 1,000 cfu/ml Review program, Immediately disinfect system, take measures to protect workers and population, review program, retest and retreat until under control

As we discussed in our previous blog posting, the new 188 standard from ASHRAE suggests developing a Water Management Program for managing the legionella risk in a facility. This Program will contain the details of control limits for various action levels and the specific actions to be taken if these limits are exceeded. Every facility should review ASHRAE Standard 188 and work to develop a program for their facility. The potential for liability exists should a catastrophic outbreak occur at a facility with no program in place. 

Where do we go from here? A facility that is currently testing for legionella needs to develop an action plan, as part of the Water Management Program, to execute proper corrective actions when and if a positive test result is obtained. By having a Water Management Program in place, the chances of ever having to address positive test results is greatly reduced. 

The Future of Cooling Tower Bacteria Safety

Where is the industry headed? Only time will tell. If New York City is any indication, they are moving forward to register every cooling tower in the city with plans to disinfect every system. See this link for the recent Health Commissioner’s Order on this subject. Being prepared for the future helps all of us and helps you to be a better resource for your customers in the event of a positive legionella test.  

This blog post is designed to help raise awareness of the legionella issue so that we are all more prepared for what could come in the future. By being prepared, we are all better suited to answer the question posed in the title… “How would you handle an outbreak?” 

Learn more about how you can properly prepare your cooling tower by talking to a water treatment expert. 

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Topics: Cooling Tower

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