Legionnaires’ disease can be fatal. Yet in the United States, cases have been increasing. 

According to the National Institutes of Health, reported cases of Legionnaires' disease have risen significantly since 2000. A separate study estimates that 8,000 to 18,000 people in the U.S. are hospitalized for the disease each year, with a fatality rate of 10%. 

Last August, New York City faced one of its largest outbreaks ever, linked to contaminated water in 12 cooling towers across 10 buildings. Dozens of people were hospitalized and several lives were lost. Earlier this year, incidents were reported in the Harlem area. There were also cases reported in Texas and Las Vegas. These are only the most high-profile examples.

Part of the problem is the lab culture testing that many states and localities reference in their rules. Although it is often referred to as the gold standard in testing, lab culture testing has serious limitations, in part stemming from the delay between testing and results. Despite the limitations, testing requirements have remained largely unchanged. 

But there are steps facilities managers can take if they want to go beyond compliance to better protect occupants from this growing public health risk. 

Hiding in plain sight

Legionnaires’ disease is a lung infection that’s caused by inhaling water droplets containing Legionella bacteria.

Although Legionella itself is naturally found in rivers, ponds and other water sources, when it enters water systems in the built environment, factors such as warm temperatures and inadequate disinfection can allow it to multiply rapidly. Common sources in buildings include cooling towers, taps, showers, air conditioning units and hot water tanks.

Increasingly complex water systems and rising temperatures are contributing to the risk.   

Importantly for facilities managers, the risk of Legionella is generally greater in commercial premises because of their larger and more intricate water systems, which tend to include cooling towers, multiple air conditioning units and extensive plumbing networks. This complexity provides more opportunities for Legionella bacteria to grow and spread. 

If there are periods of low occupancy or disuse, that can further the risk due to water stagnation, which creates ideal conditions and breeding grounds for Legionella growth. 

Best practice challenges

The widely adopted ASHRAE Standard 188, developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, provides a framework to implement comprehensive water management programs that control risks related to the growth and transmission of Legionella in building water systems, including through the use of regular monitoring and maintenance. Many states and cities also stipulate their own standards, especially in jurisdictions with recent outbreaks or stricter health requirements.

There is room for facilities managers to do more, though. 

One of the most critical weaknesses exposed by outbreaks like New York’s is the lag between contamination and confirmation. 

Traditional Legionella testing methods rely on laboratory culturing, which takes up to ten days to deliver results. Yet Legionella can double in a day. In a large building or cooling system, that delay can mean the difference between early intervention and widespread exposure. Water samples can also get damaged in the transportation process, potentially killing the Legionella inside and leading to a false negative result. In addition, culture-based testing cannot detect viable but non-culturable Legionella, which, though dormant, can resuscitate and cause an infection.

Importantly too, buildings will often continue to operate as normal during the waiting period. That potentially disperses contaminated aerosols into the surrounding environment. As a result, conventional testing methods often confirm the presence of Legionella only after exposure has already occurred — by which point the opportunity for prevention has been missed.

From compliance to control

Facilities managers can address these gaps by prioritizing more frequent and more robust water quality testing. 

First, use quicker testing more frequently. The latest generation of rapid testing kits enable the detection of Legionella in just 25 minutes and are accurate at detecting the most common and potentially fatal species of Legionella bacterium — Legionella pneumophila. 

Quick detection of Legionella pneumophila empowers facilities managers and others with responsibility over water systems to react promptly to contamination, thereby minimizing the risk of exposure and human infection. Not only does using rapid testing kits help reduce risk and minimize exposure to building occupants, it also offers additional information during reviews of the risk assessment.

Second, transition water management plans from static compliance documents to dynamic, living systems. As a dynamic plan, it should incorporate continuous monitoring of temperature, disinfectant levels and flow — combined with rapid on-site testing — to create a real-time feedback loop that drives ongoing risk reduction and system optimization.

Third, make education part of the plan. As Legionella risk evolves, facilities managers and their teams that stay up to date on guidance, testing innovations and risk factors will be better equipped to identify vulnerabilities before they escalate. Regular training helps ensure an understanding of how Legionella behaves, where it hides and how system design, temperature control and maintenance practices influence bacterial growth.

As frontline defenders against Legionella bacterium, facilities managers can play a leading role in occupant safety. By pivoting from a reactive to a proactive plan, they have an opportunity to raise the bar in watertight Legionella control.