June 19, 2024

Beyond the Microscope: Advanced Legionella Detection Techniques

Legionella Testing: Why Regular Testing is Essential for all Buildings

Legionella is a type of bacteria that can cause a serious type of pneumonia called Legionnaires’ disease. While Legionella bacteria naturally occur in water environments, they can multiply and spread in human-made building water systems such as hot water systems, cooling towers, and decorative fountains. This poses a risk to human health, especially for older adults, smokers, heavy drinkers, or those with weakened immune systems or lung disease. Regular Legionella testing of water systems is crucial to detect any presence of the bacteria and take prompt actions to eliminate it. This article discusses why Legionella testing is essential for all types of buildings.

Importance of Testing in Different Building Types

Hospitals and Healthcare Settings
With patients who are at high risk of Legionella infection due to their health conditions, it is extremely important for hospitals and other healthcare settings to implement a rigorous Legionella testing and prevention program. Healthcare facilities need to test their water systems on a monthly basis to ensure there is no presence of Legionella bacteria that could potentially infect vulnerable patients. Any positive results must be properly investigated and remediated to keep patients safe.

Hotels and Accommodations
Hotels, motels and other commercial accommodations host thousands of guests every year, including elderly travelers and those with underlying illnesses who may be at risk. These properties need to test their water systems, particularly hot water storage tanks and distribution systems, on a quarterly basis minimum. Positive test results require thorough disinfection of the entire system to eliminate bacteria before guests can utilize those areas again. Routine testing helps address any hidden issues before they impact hotel patrons.

Office Buildings
While the risks may be relatively lower than hospitals, offices still need testing programs due to staff density and occupancy levels. Systems in large commercial office towers should be tested at least twice a year. This ensures prompt remedial actions if contamination is found in any components including air conditioning cooling towers that could spread bacteria through the building. Regular testing provides assurance to employees and helps fulfill building safety responsibilities.

Why Different Building Areas Need Specific Testing

Cooling Towers and Condenser Water Systems
Cooling towers that use re-circulating water as part of air conditioning systems present particularly high risks as they can spread Legionella aerosols over long distances. These towers need monthly testing along with intensive monitoring of critical control points like biocide residuals in sumps and basins. Any towers testing positive should not be used until disinfection is complete.

Showers and Faucets
While hot water tanks tend to be the prime sources of Legionella, bacteria can also build up at points of use like showers if temperatures are sub-optimal. Healthcare facilities and hotels should test showerheads and faucets quarterly to quickly detect issues. This avoids contamination spreading to vulnerable people directly from points where they wash.

Decorative Water Features
Outdoor and indoor fountains present challenges as they are exposed to ambient temperatures and lower chlorine residuals compared to utility water. Monthly testing and shock dosing is advisable along with installing UV disinfection to keep features bacteria-free. Positive results necessitate draining, scrubbing, high heat flushing and refilling systems.

Pipework and Distribution Networks
While tanks and equipment are more commonly tested, it is also important to take samples from distal locations within pipework to check for contamination further away from sources. Hotels should test at least one outlet each in a few rooms periodically to check the distribution network. This helps pinpoint any pockets of bacteria that require more extensive remediation work in those sections.

Interpreting Test Results and Setting Action Levels

Legionella culture testing looks for the presence or absence of live bacteria colonies. PCR (Polymerase Chain Reaction) tests detect bacterial DNA fragments and can find Legionella at much lower detection limits than standard cultures. Both methods are suitable with action levels typically set as:

– Less than 100 CFU/L (Colony Forming Units per Liter) – System under routine monitoring

– 100-1000 CFU/L – Elevated levels requiring evaluation of control measures and re-testing within 7 days

– Over 1000 CFU/L or positive PCR – Considered contaminated necessitating thorough cleaning and disinfection

While guidelines recommend remediating all positive detections, a risk assessment of the system, users and previous readings helps decide the most appropriate response in each case. Close monitoring of control parameters also indicates if conditions are conducive for potential outbreaks.


Given the serious nature of Legionnaires’ disease, all buildings especially those housing high-risk occupants need to have effective Legionella testing programs in place to fulfill their health and safety responsibilities. Routine culturing of potential sources per standard protocols, along with interpreting results prudently, are key to prompt detection and remediation of issues before they impact occupants. Regular testing should be seen not just as a regulatory requirement but as a critical maintenance activity keeping indoor water infrastructure Legionella-free and safe for public health.


  1. Source: Coherent Market Insights, Public sources, Desk research
  2. We have leveraged AI tools to mine information and compile it