With the number of reported cases of Legionnaires’ disease having risen by 200% in the past 10 years. Other estimates suggest that Legionnaires’ disease now affects tens of thousands of people in the U.S. each year, and the consensus among health experts is that this upward trend is likely to continue.
There are several factors that may help explain the recent surge in cases of Legionnaires’ disease — a potentially fatal form of pneumonia caused by inhaling Legionella bacteria.
Foremost, Legionella thrives between 77°F and 113°F. As climate change continues to alter our environmental conditions, rising temperatures, longer warm seasons and shifting rainfall patterns are creating more favourable conditions for Legionella to thrive in water systems.
At the same time, many distribution systems and plumbing networks across the country suffer from aging pipes, oversized layouts and stagnant dead-ends. These low-flow zones diminish disinfectant residuals, promote biofilm formation and create pockets where Legionella can multiply unchecked. Many legacy plumbing systems also lack modern design features, such as efficient temperature control and disinfection mechanisms, that help prevent bacterial growth.
Importantly, the risk of Legionella proliferation is even more profound in water utility systems, as research reveals that rising average air and ground temperatures can increase the base temperature of cold water systems, potentially leading to increased Legionella growth in both cold and hot water distribution. Moreover, rapid shifts from drought to downpours, something which is becoming more common in all areas of the world, are known to create favourable conditions for Legionella growth in water distribution systems. At the same time, rising temperatures also increase demand for water sources, placing a new strain on water utilities.
So, what is to be done? Foremost, the recommendation is for water professionals with the standard lab-culture method as the oldest and most widely accepted technique for the detection of Legionella bacteria. However, this approach has limitations that can hinder timely responses to potential outbreaks.
Lab culture testing is also unable to detect Viable but Non-Culturable Legionella (VBNC) — which, though dormant, can still be incredibly dangerous due to their ability to resuscitate and cause an infection. The result can be a false sense of security, with the potential for lab results to state a negative outcome when repeated tests confirm non-conformance.
Arguably, then, as the challenges posed by Legionella evolve, there is a clear case for water utilities to reconsider their testing strategies and embrace more innovative, efficient methods.
One such example can be found in the latest generation of rapid Legionella testing, which has been purposefully designed to overcome the limitations of traditional Legionella detection by providing on-site testing without the need for lab facilities. Incredibly easy to use, these tests enable duty holders to inspect water systems in only 25 minutes and provide an accurate and reliable result on the presence or absence of Legionella pneumophila bacteria — the primary cause of Legionnaires’ disease.
In this way, the ability to gain an immediate picture of Legionella empowers water professionals to react promptly to contamination and take appropriate action, thereby significantly minimising the risk of exposure.
Source:Greg Rankin
Date:Dec. 8, 2025
