Legionella and the Next Generation of Workplace Detection

As Legionella continues to hit the headlines, Greg Rankin CEO at Hydrosense considers how occupational health and safety professionals, employers and facility managers can strengthen their approach to detection and control.

• By Greg Rankin
• Oct 02, 2026

Early in 2026, we witnessed significant Legionella outbreaks across the US, including a deadly cluster in Ector County, Texas, cases linked to a major apartment complex in Harlem, New York City and an outbreak associated with a Las Vegas casino.

Then, more recently, this summer saw New York experience another Legionnaires’ disease cluster, with 11 people dying and more than 90 falling ill. This follows last summer’s deadly Harlem outbreak, in which seven people died and more than 100 people became ill after exposure to Legionella.

While the specific circumstances behind each incident may differ, one truth that remains abundantly clear is that Legionella cases are rising at an alarming rate across the US.

For occupational health and safety (OHS) professionals, the implications are profound.

Any workplace with a complex water system can potentially become an environment in which Legionella grows and exposes workers, contractors, visitors or other building occupants. Equally, aside from the grave safety implications, an outbreak carries significant potential consequences in terms of liability, business disruption and reputational damage.

The result is that it is becoming increasingly important for those responsible for workplace safety to take a much more proactive, pre-emptive approach to Legionella risk, ensuring that controls are robust, effective and regularly reviewed. But what does that look like in practice?

A rapidly rising risk

Before answering that question, it is important to first explain the several factors attributed to Legionella’s recent ascent. 

As most OHS professionals will already know, Legionella thrives in warm, stagnant water with the optimal temperature range for growth between 77°F and 113°F.  As climate change continues to alter environmental conditions, rising average temperatures, prolonged warm seasons and shifting rainfall patterns are contributing to more favorable conditions for Legionella growth within building 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.

Combine all these factors, and it may be easy to see why Legionella cases in the US have seen a 1,000 percent increase in the past two decades alone1 and are on an upward trajectory that experts predict will continue if not addressed.

The result is that it is becoming more important than ever for safety and facilities managers to pay extra diligence to how they assess, test and control the risk of exposure to Legionella bacteria in the face of increasing risk. For many, though, there remains a certain lack of clarity and standardization about what best approach to take.

Best practice, beyond compliance

In the US, OSHA's General Duty Clause requires employers to provide a workplace free from recognized hazards that are causing or are likely to cause death or serious physical harm. OSHA also provides technical guidance on Legionella through its Technical Manual, including information on assessing and controlling workplace exposure.

For employers, the implication is important - Legionella management should not be approached simply as a question of meeting a particular testing requirement. It should form part of a broader program for identifying hazards, implementing appropriate controls and demonstrating that those controls are being maintained.

ASHRAE Standard 188 also provides an important framework for managing Legionella risk in building water systems. Water Management Plans based on recognized guidance can help organizations identify hazardous conditions, establish control measures, monitor those controls and determine appropriate corrective action. Many states and cities also stipulate their own specific standards, especially in jurisdictions with recent outbreaks or stricter health requirements.

From our extensive experience in the Legionella field, though, we believe that current recommended practice simply doesn’t go far enough and there is scope to do much more to raise the bar on safety through a more robust and proactive approach to water safety.

Technological advantages

One of the most critical weaknesses exposed by many recent outbreaks 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 (VBNC) Legionella, which, though dormant, can resuscitate and cause an infection. This can create a false sense of security, with lab results showing a negative outcome when repeated tests confirm non-conformance.

Arguably then, as Legionella risk evolves, best practice now demands a move beyond the lab-culture status quo.

Proactive rather than reactive maintenance is critical. OSH professionals and facilities teams should advocate for and implement robust maintenance schedules that include regular flushing, disinfection and temperature checks. Safety teams and duty holders should combine active temperature management with more advanced, rapid Legionella testing regimes to ensure real-time alerts for contamination, allowing rapid intervention before bacteria proliferate. Not only does this approach minimize potential exposure, but it also offers additional information during necessary reviews of risk assessment and provides peace of mind for tenants.

Training and awareness are also key. Workplaces that understand the latest Legionella research, emerging risk and technological solutions are better equipped to provide guidance and solutions to occupants. Staff and contractors should also be properly informed and empowered to respond quickly to any suspected risk. Failure to do so doesn’t just implicate reputational harm - it can result in loss of life. After all, the large majority of Legionella outbreaks are preventable. Research shows that among 23 outbreaks evaluated by CDC, investigators identified process failures in 65%, human errors in 52%, equipment failures in 35% and unmanaged external changes in 35%. Nearly half (48%) involved deficiencies in multiple categories. Cultivating a culture of awareness is therefore critical to negating these unnecessary risks.  

Making Legionella control watertight

If the recent flurry of Legionella outbreaks seen this year has taught the health and safety world anything, it is that we cannot afford to underestimate the scope of Legionella risk. In the context of what is becoming an increasingly complex workplace safety concern, effective management and control can only be achieved by going beyond compliance with proactive monitoring, rigorous control measures and a culture of continuous oversight that is truly watertight.

Immediate actions for OHS professionals

• Review your Legionella risk assessment: Identify building systems and processes that could create exposure, including areas of stagnation, low flow, inadequate temperature control or aerosol generation.
• Check your Water Management Plan: Confirm that responsibilities, control measures, monitoring procedures and corrective actions are clearly defined and understood by the duty holders responsible for the facility.
• Map higher-risk areas: Pay particular attention to complex plumbing systems, cooling equipment, areas that have experienced shutdown or low occupancy and locations where workers could encounter aerosolized water.
• Review your testing strategy: Understand where conventional laboratory culture is appropriate and whether rapid testing could provide useful additional information during investigations, after periods of stagnation or when verifying corrective actions.
• Define your response before an incident occurs: Establish what happens when a test indicates potential contamination, who decides to intervene and when confirmatory laboratory testing is required.
• Document corrective action: Record findings, interventions and verification activities so that the organization can demonstrate that identified risks are being actively managed.
• Keep the program under review: Legionella control is not a one-off exercise. It’s vital to continue reassessing the water system and the effectiveness of existing controls when buildings, occupancy, equipment or operating conditions change.