To safeguard the health of building occupants, nearby personnel and even individuals innocently passing nearby, professionals who design and install chiller systems with cooling towers seek solutions that reduce the chance of spreading the potentially deadly Legionella bacteria causing Legionnaire’s disease. 

Fortunately, continuous monitoring devices are now on the market that can detect airborne Legionella and provide automatic notification within a matter of hours. This not only eliminates waiting days for outside lab results, but also enables a proactive response, dramatically reducing the risk of a devastating outbreak or costly litigation.


Legionnaires’ disease in HVAC systems

Legionnaires’ disease is a severe, even fatal form of pneumonia caused by the bacteria. According to the Centers for Disease Control and Prevention, about 6,100 annual cases of Legionnaires’ disease were reported in the United States in 2016, with one of every 10 dying.

Although Legionella is naturally found in bodies of water and in the majority of building water systems, the highest risk is when the bacteria becomes airborne in mist, spray or droplets that can be breathed into the lungs.

This is where cooling towers play a critical role. In HVAC, cooling towers often are used in conjunction with chillers for large building cooling systems. A recent CDC study involving 196 cooling towers nationwide found 84% contained Legionella DNA in the water.

The problem is that cooling towers by their very nature use evaporative methods to rapidly cool the water in the system. This can cause “drift” — a fine mist — that can travel long distances based on wind speed, building height and cooling tower location.

For buildings where cooling towers are installed on roofs in the nearby vicinity of fresh-air intake systems — as often is the case — this could expose the building’s occupants to the bacteria. It also can pose a risk to nearby building personnel conducting maintenance.

When drift is considerable, it can affect individuals in nearby buildings, parking lots and even on the street. Reports show airborne Legionella can travel as far as one mile in some instances.

Such was the case in a recent national news report where Disneyland had to shut down two cooling towers located more than 100 ft. from areas accessible to guests that were ultimately found to have Legionella. According to the Los Angeles Times, in the Legionnaires’ disease outbreak, 11 of 15 people infected had visited the park and four had not — including two who died.

These and other incidents are serving as a wakeup call for HVAC industry professionals that utilize cooling towers with chillers.


Continuous monitoring for airborne Legionella

Today simple, economical and automated systems can provide continuous monitoring for airborne Legionella. Automatic notification to cloud networks and mobile devices warn of initial detection of the bacteria, followed by full confirmation in a matter of hours.

This stands in stark contrast to the days or even weeks of shipping samples to offsite labs before receiving results.

Current testing methods typically involve infrequent, such as monthly or quarterly, tests using settle plates that contain cultured media exposed to the air that are then incubated, or impactors that must be sent to a third-party lab for analysis. For these types of tests, it can be three days before the results are available.

Tests also are often performed on the water itself, which can demonstrate the presence of Legionella but not determine if there is any airborne risk.

Instead, continuous monitoring devices such as PathogenAlert’s RAPID (Rapid Airborne Pathogen Identification and Detection) Reader System can detect and confirm the presence of airborne Legionella within hours of sampling. 

The small wireless device mounts anywhere and operates by automatically sampling the air in cooling towers, chillers, ducts or other high-risk areas every five minutes (or any other specified timeframe) on a 24/7 basis. Air is drawn in and flows across the cartridge, allowing any Legionella microbes to settle on a nutrient-rich site where it then begins to grow.

To detect pathogen growth, the device uses optical measurement and laser technology, along with electronic digital signal processing. Inhibitors are utilized to eliminate false readings. Detection software also monitors for erratic behavior that can be caused by nonpathogenic particles, such as dust, and compensates appropriately. The cloud-based platform allows continuous, remote online monitoring of individual or multiple locations from a laptop “dashboard” that consolidates key data for review. Alarms and notifications can be sent to any mobile device.


Early detection equals early remediation

One of the primary goals of early detection is to allow existing and effective techniques to be implemented as quickly as possible to destroy Legionella bacteria.

Traditional methods are water chemicals and disinfectants. Unfortunately, these methods are ineffective against Legionella that already is in the air.

There are, however, other options. Germicidal UV light systems destroy Legionella in seconds. At a specific wavelength, UV-C deactivates the DNA of bacteria, viruses and other pathogens, which eliminates its ability to multiply and cause disease. This tool when bundled with automated airborne Legionella sensors is an effective seek-and-destroy tool for the remediation of Legionella.

With airborne Legionella and cooling towers still making news headlines together, it is time for HVAC professionals to look into automated testing and treatment options that can identify and handle the problem before it becomes a news-generating event.