Legionella and Legionnaires Disease – Which Sectors Are At Risk?
If Legionella bacteria enters the water systems in our buildings, the water outlets we use can become a risk to our health and wellbeing. Any industry that has water facilities, that humans interact with, should have greater awareness and understanding of the potential impact of Legionella and how to manage this health risk.
Hydrosense rapid Legionella tests could be the perfect companion to existing water management programs as they give real time results for the species of Legionella that causes most Legionnaires’ disease outbreaks. Protecting the lives of your staff, customers and visitors should be your top priority because it could be the difference between a trusted brand reputation and financial ruin.
Look at each sector to better understand the risks and see how Hydrosense could support you in your quest for improved public health protection against Legionella pneumophila.
Legionella Risk in Hospitals and Care Homes
Legionnaires’ disease is a serious risk in healthcare settings. Cases of healthcare-acquired Legionnaires’ disease are on the rise, posing a particularly grave threat in hospitals and care homes where vulnerable populations reside. In fact, 1 in 4 people who contract Legionnaires’ disease in healthcare facilities will not survive.1
To protect the health and safety of patients and residents, healthcare facilities must take stringent precautions against Legionella. Proactive Legionella management is not just a regulatory requirement but a life-saving necessity in environments where risk factors are high and the impact can be devastating.
- A CDC study found that 18% of confirmed Legionnaires’ disease cases are linked to healthcare facilities.2
- Legionella pneumophila was found in 70% of US hospitals surveyed across 13 states.3
- 80% of definite healthcare-associated cases were linked to long-term care facilities.4
- The death rate may be as high as 40–80% in untreated immuno-suppressed patients.5
Factors Affecting Increased Risk of Legionella in Healthcare Facilities:
- High-Risk Population: Patients in healthcare facilities are often highly susceptible to infection. Immunocompromised individuals, recent surgical patients, and those dependent on respiratory devices face an elevated risk. Vulnerable populations, including smokers, the elderly, and newborns, are especially susceptible.
- Aerosol-Generating Devices: Legionella spreads through aerosols, which can originate from any water source that creates mist. Common sources in healthcare include showers, humidifiers, birthing pools, and respiratory devices, making these high-risk zones for Legionella proliferation.
- Complex Plumbing Systems: Older healthcare facilities or those with recent renovations often have intricate plumbing systems with “dead legs” where water can stagnate, creating ideal conditions for Legionella growth. Additionally, outdated or incomplete schematics of water systems can make it challenging to monitor and address potential risks.
- Inadequate Water Management Plans: Many healthcare facilities have water safety plans that meet minimum regulatory standards, but these may not be comprehensive enough to prevent Legionella growth entirely. Effective Legionella control requires detailed, proactive water management tailored to the unique risks in each facility.
- VBNC Legionella Risks: Recurring Legionella issues, despite negative lab tests, may indicate VBNC (Viable But Non-Culturable) bacteria. These dormant bacteria evade lab detection but can reactivate, causing reinfection and non-conformance, posing serious risks to patient safety and compliance.
- Limitations of Traditional Testing: Conventional Legionella testing, which involves sending water samples to external labs, has limitations. This method can delay detection, allowing bacteria to proliferate between testing intervals. Faster, real-time solutions are essential for environments where quick action can prevent outbreaks. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing the Legionella Risk in Hospitals and Care Homes:
Understand the Stakes: Legionnaires’ disease kills approximately 1 in 10 infected individuals, with the mortality rate rising to 1 in 4 in healthcare settings.1 Given the high fatality rate, healthcare facilities must adopt rigorous Legionella control practices.
Develop a Comprehensive Management Plan: A detailed Legionella risk management plan should include preventive measures, regular testing protocols, and emergency actions. This plan acts as a foundation for effective, ongoing risk mitigation.
Eliminate Stagnation Points: Legionella thrives in stagnant water. Remove any “dead legs” or areas of low flow within plumbing systems to keep water circulating and minimise bacterial growth.
Control Water Temperature: Maintain hot water above 60°C and cold water below 20°C to deter Legionella growth. When temperature control isn’t feasible, incorporate biocide treatments to help maintain water safety.
Conduct Regular Testing: Routine Legionella testing is essential, especially in high-risk areas. Testing should be frequent and allow for rapid remedial action, reducing the risk of outbreaks in environments with vulnerable populations.
Thermostatic Mixing Valves (TMVs): TMVs are essential for controlling water temperatures in healthcare settings to prevent scalding injuries. They regulate water to safer temperatures for these populations by blending hot and cold water, often lowering temperatures to a range where Legionella can thrive (20 – 45°C). Biofilm can also build up in the complex components of these units where Legionella can hide and be protected. Read more about the risks here.
85% of all Legionnaires’ disease outbreaks were attributed to water system exposures that could have been prevented by effective water management programs.4
Use Rapid Testing Technology: Traditional laboratory testing can delay results, putting lives at risk. Hydrosense’s on-site Legionella test provides results within 25 minutes and can detect VBNC Legionella, offering a fast Yes/No answer to help staff make immediate, informed decisions and protect vulnerable patients and residents more effectively.
References
- https://www.cdc.gov/legionella/about/index.html
- https://www.cdc.gov/legionella/health-depts/surv-reporting/2018-19-surv-report-508.pdf
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6982084/#:~:text=Somewhat%20alarmingly%2C%20Legionella%20pneumophila%20was,diseases%20encountered%20in%20the%20winter.
- https://pmc.ncbi.nlm.nih.gov/articles/PMC5720245/
- https://www.who.int/news-room/fact-sheets/detail/legionellosis
Legionella Risk in Swimming Pools
Swimming pools are a potential source of disease for infections including Legionnaires’ disease, which is caused by Legionella pneumophila. Swimming pools are popular in gyms, spas, leisure resorts, hotels and even in people’s back gardens.
Worldwide there are approximately 13 million swimming pools with the majority of them in North America (59%) and Europe (29%).1
- In the United States, there are 10.7 million swimming pools, with 10.4 million in residential homes and 309,000 in public spaces.2
- Australia has the highest per capita pool ownership in the world, with 1.6 million domestic swimming pools.3
- In the UK, 84% of the population lives within two miles of a swimming pool.4
- In China, there are 36,000 swimming venues, with 54% being outdoor pools and 44% being indoor pools.5
- In Italy, there are about 300,000 private pools, with 250,000 being in-ground and 50,000 being above ground.6
Although swimming pools themselves are generally considered lower risk for Legionella outbreaks due to chlorination levels, they are not completely without risk. The main risk appears to be associated recreational water facilities related to swimming pools.
One study, highlights that investigated cases and outbreaks of Legionnaires’ disease in swimming pools and spa pools, showed that from all reported cases of infection 43% were diagnosed with Legionnaires’ disease, with a fatality rate of 6.3%.7 In the US between 2000 and 2014, the Centers for Disease Control (CDC) noted that the number of outbreaks of Legionella in recreational water increased by 14% per year.8
Factors Affecting Increased Risk of Legionella in Swimming Pools:
- Water Temperature: Legionella bacteria thrive in warm water, typically between 20°C and 45°C. Heated swimming pools, particularly those maintained at temperatures comfortable for prolonged swimming, can provide an ideal environment for Legionella growth.
- Aerosol Generation: Activities that create water droplets or mist, such as splashing, swimming, pool jets, and water features, increase the risk of Legionella transmission. When these aerosols are inhaled, they can carry the bacteria into the lungs, leading to infection.
- Inadequate Filtration and Disinfection: Poorly maintained filters or insufficient disinfectant levels can allow Legionella to proliferate.
- Biofilm Formation: Biofilms are protective layers that hide and protect Legionella, they form on surfaces within pool systems, such as pipes, tiles, and other water-carrying infrastructure. Biofilms shield bacteria from disinfectants, making them more difficult to eradicate.
- Complex Pool Plumbing Systems: Pools with extensive or poorly designed plumbing systems may have “dead legs” or areas of stagnant water, where Legionella bacteria can grow. Stagnant water and low-flow areas are particularly conducive to bacterial growth.
- Water Source and Quality: The quality of the water supplied to the pool can influence Legionella risk. Pools filled with water that already contains organic materials or minerals may have an increased likelihood of bacterial contamination if not treated properly.
- Increased Water Temperature: In hot climates, high ambient temperatures can raise the pool water temperature, sometimes bringing it into the range where Legionella bacteria thrive (20°C–45°C). Warmer water temperatures can reduce the effectiveness of disinfectants, as higher temperatures can accelerate biocide evaporation and degradation.
- Poor Maintenance Practices: Inconsistent cleaning, infrequent inspection of pool systems, or improper handling of chemical balances can lead to Legionella growth.
- VBNC Legionella Risks: Recurring positive Legionella results in swimming pools, despite negative lab test results, may indicate the presence of VBNC (Viable But Non-Culturable) Legionella. These dormant bacteria evade detection by standard testing methods but can reactivate in warm temperatures and stagnant water. This poses a significant risk to swimmer health and safety. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing the Legionella Risk in Swimming Pools:
Maintain Optimal Water Temperature: Keep pool water below 20°C when possible, as Legionella bacteria thrive in warmer water (20°C – 45°C). For heated pools, ensure that the water temperature does not exceed safe levels to limit bacterial growth.
Ensure Effective Filtration and Disinfection: Use proper filtration and maintain adequate disinfectant levels, such as chlorine or bromine, to keep water clean and minimise bacterial presence. Regularly check and adjust chemical levels to ensure they remain effective, especially in hot weather.
Regularly Clean and Inspect Pool Systems: Clean filters, pipes, and any areas that might accumulate biofilm or debris. Regular maintenance of pool equipment helps prevent biofilm formation, where Legionella bacteria can thrive.
Monitor and Control pH Levels: Keep the pool’s pH between 7.2 and 7.8, as this range optimises the effectiveness of chlorine and other disinfectants, helping to control bacterial growth.
Address Areas of Stagnant Water: Ensure water circulation throughout the entire pool system, including pipes and any attached water features, to prevent areas of stagnant water where Legionella can grow.
Conduct Regular Legionella Testing: Implement a routine Legionella testing program to monitor for the presence of the bacteria, particularly in heated pools and those with high aerosol exposure.
Use Rapid Testing Technology: Traditional laboratory testing for Legionella can be time-consuming, which may delay critical actions needed to keep swimming pool water safe. Hydrosense’s on-site Legionella test provides results in just 25 minutes, delivering a clear Yes/No answer that allows pool staff to make immediate, informed decisions. This rapid testing solution enables quicker responses to potential risks, helping to protect swimmers and maintain safer water quality.
References
- https://cordis.europa.eu/project/id/604884/reporting#:~:text=On%20a%20global%20level%20there,million%20swimming%20pools%20(12%25)%20
- https://www.rubyhome.com/blog/swimming-pool-stats/#:~:text=There%20are%2010.7%20million%20swimming,number%20of%20swimming%20pools%20nationwide
- https://environpools.com.au/news/the-australian-pool-ownership-phenomenon/#:~:text=Pool%20Lighting-,The%20Australian%20Pool%20Ownership%20Phenomenon,pool%20ownership%20in%20the%20world
- https://www.leisuredb.com/blogs/2019/6/7/2019-state-of-the-uk-swim-industry-report-out-now#:~:text=The%202019%20report%20shows%20that,of%20the%20water%20keeps%20expanding
- https://www.statista.com/statistics/1199239/china-number-of-track-and-field-venues-and-swimming-pools/#:~:text=As%20of%20December%202022%2C%20there,such%20as%20lakes%20and%20beaches
- https://www.italianpooltechnology.com/news/italian-pool-market#:~:text=Yet%2C%20we%20can%20make%20some,for%20approximately%2060%20million%20inhabitants
- https://www.ncbi.nlm.nih.gov/pubmed/30061526
- https://www.urisk.co.uk/legionella-in-swimming-pools/
Legionella Risk in Spa's and Hot Tubs
Spa-pool systems, which include whirlpools and hot tubs, are a well-known source of disease for infections including Legionnaires’ disease, which is caused by Legionella pneumophila. Hot tubs or spa pools are popular in gyms, hotels and increasingly in people’s back gardens.
Whilst hot tubs and spas pools in both residential and commercial locations pose a risk, it is the commercial hot tub segment that is anticipated to grow at a higher rate compared to the residential segment.1 This faster growth is attributed to several factors:
- Rapid expansion in the hotel, salon, and spa industries.
- Increasing integration of hot tubs into hospitality, wellness, and recreational facilities.2
- Growing demand in hotels, resorts, spas, and fitness centres to enhance guest experiences.
- Rise of wellness tourism and experiential travel.
- From November 2022 to June 2024, 12 cases of hot tub related Legionnaires’ disease were reported to the CDC among travellers on two cruise ships, with 8 cases on one ship and 4 on another.3
- In a 2017 outbreak in Palmanova, Spain, 27 cases of Legionnaires’ disease were linked to outdoor hot tubs, with extremely high concentrations (>10^6 CFU/L) of Legionella pneumophila found in the hot tubs on the terraces of vacant hotel rooms.4
- The CDC investigation of cruise ship outbreaks found that private hot tubs were operating at temperature ranges of 77 to 113 degrees Fahrenheit (25-45°C) for several days without draining and with no residual disinfectant, creating ideal conditions for Legionella growth.5
- A study, that investigated cases and outbreaks of Legionnaires’ disease in swimming pools and spa pools, has shown that from all reported cases of infection 43% were diagnosed with Legionnaires’ disease, and found a fatality rate of 6.3%.6
Factors Affecting Increased Legionella Risks in Hot Tubs/Spa Pools.
- Optimal Temperature for Legionella Growth: Legionella bacteria require a temperature range of 20oC to 45oC to flourish and multiply. The water in hot tubs is kept at between 37oC and 40oC (98oF to 104oF),7 which provides the ideal temperatures for Legionella bacteria to grow.
- Complex Design and Biofilm Accumulation: The intricate systems of filters, pumps, and pipes in spa pools provide significant surface areas for biofilm formation. Biofilm serves as a protective layer for Legionella, shielding it from biocides and other treatments. Proper management of these components is crucial to maintain water purity and control bacterial levels. Routine testing and chemical and microbiological monitoring are vital parts of any effective spa-pool maintenance regime.
- Aerosol Generation: The bubbling and splashing in hot tubs generate aerosols, which can release contaminated water droplets into the air. When these droplets contain Legionella, they pose a significant inhalation risk. Prolonged exposure near such sources can increase the likelihood of infection, with research indicating that the risk of contracting Legionnaires’ disease rises by 64% for every hour spent near a contaminated source.8
- External Microbiological hazards: Environmental factors such as weather, air quality, and surrounding surfaces can introduce additional threats, fostering Legionella growth.
- Limitations of Traditional Testing Methods: Spa pool managers often rely on sending water samples to laboratories for Legionella testing, which is a long-established practice. However, recent studies have highlighted significant limitations of these traditional lab culture methods. For example, lab tests may underestimate Legionella levels or miss certain strains entirely. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing the Legionella Risk in Hot Tubs and Spa Pools:
Maintain Optimal Water Quality: Regularly monitor and adjust pH and disinfectant levels to maintain water balance and prevent bacterial growth.
Clean and Disinfect Regularly: Routinely clean and disinfect filters, pipes, and all surfaces where biofilm may develop.
Perform Frequent Microbiological Testing: Use reliable testing methods regularly to ensure accurate detection of Legionella.
Manage Aerosol Generation: Reduce unnecessary splashing or bubbling and ensure proper ventilation around the hot tub area to minimise aerosol spread.
Implement a Robust Maintenance Schedule: Develop a clear maintenance plan, including regular water changes and inspections of all system components.
Train and Educate Staff: Ensure that all individuals responsible for maintaining the spa pool are trained in Legionella risk management and best practices.
Leverage Rapid Testing Solutions: Conventional lab testing often involves delays, increasing the risk of exposure. The Hydrosense on-site Legionella testing solutions deliver results in just 25 minutes, enabling staff to make swift, informed decisions and enhance protection for vulnerable individuals.
References
- https://www.mordorintelligence.com/industry-reports/hot-tub-market
- https://www.gminsights.com/industry-analysis/hot-tub-market#:~:text=Hot%20Tub%20Market%20size%20was,segment%20catering%20to%20luxury%20upgrades.&text=Growth%20Drivers:,Home%20improvement%20trend
- https://www.cidrap.umn.edu/legionella/cdc-traces-legionnaires-outbreaks-2-cruise-ships-hot-tubs
- https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1137470/full
- https://www.foxnews.com/health/legionnaires-disease-outbreak-linked-cruise-ship-hot-tubs-cdc-says
- https://cordis.europa.eu/project/id/604884/reporting#:~:text=On%20a%20global%20level%20there,million%20swimming%20pools%20(12%25)%20.
- https://www.aquawarehouse.co.uk/post/what-temperature-should-a-hot-tub-be
- http://www.hottubretailer.co.uk/2016/03/hot-tub-retailers-targeting-record-totals/
Legionella Risk in Hotels
Legionnaires’ disease was first identified during a 1976 outbreak at an American Legion convention held at the Bellevue-Stratford Hotel in Philadelphia. This event sadly led to 221 cases and 34 deaths, marking a pivotal moment in understanding Legionella as a serious waterborne pathogen associated with poorly maintained water systems in hospitality environments.
Hotels face a heightened risk of Legionella outbreaks due to the unique challenges posed by high guest turnover, complex water systems, and seasonal unoccupancy rates. With approximately 17.5 million guestrooms in over 187,000 hotels worldwide,¹ the sheer scale of the hospitality industry highlights the critical importance of proactive Legionella management.
- 32% of hotel rooms globally remain unoccupied on average,² increasing the likelihood of water stagnation and biofilm formation.
- Around 20% of reported Legionnaires’ disease (LD) cases worldwide are associated with recent travel.³
- Over 80% of 197 hotel-associated Legionnaires’ disease cases were linked to cooling towers and/or potable water systems.4
- In a study analysing travel-associated Legionnaires’ disease (TALD) surveillance data from Germany during 2015-2019, a total of 307 TALD cases in hotels were reported.5
- The Atlanta Sheraton Hotel outbreak resulted in one death, 12 confirmed cases, and 63 probable cases of Legionnaires’ disease. The hotel was forced to close for several weeks, and a lawsuit was filed against the hotel owners, management, and contractors responsible for water system maintenance.6
Factors Affecting Increased Legionella Risks in Hotels and Resorts.
- Seasonal or Infrequent Occupancy: With nearly one-third of hotel rooms unoccupied at any given time, water stagnation in pipes, tanks, and fixtures becomes a significant risk factor. Stagnant water provides ideal conditions for Legionella to multiply, particularly in dead legs or underused sections of the plumbing system.
- Complex Water Systems: Hotels feature intricate plumbing systems that include showers, pools, hot tubs, and decorative fountains. These water systems often have areas where biofilm, a protective layer for Legionella, can develop, making disinfection more challenging.
- Aerosol-Generating Features: Common hotel amenities like hot tubs, spa pools, and fountains generate aerosols that can catapult Legionella into the air, where it may be inhaled by guests and staff, leading to potential infections.
- Cooling Towers – Legionella Hotspots in Hotels: Cooling towers in hotels and resorts pose a significant Legionella risk because they generate aerosolised water droplets that can spread the bacteria over large areas.
- Unclear or Minimal Water Management Plans: Many hotels rely on reactive measures or minimal compliance with regulations. However, robust water safety plans that account for the unique challenges of hotel operations are necessary to effectively control Legionella risks.
- Reputational Damage: Outbreaks associated with a hotel’s water systems can lead to severe reputational harm, loss of business, and potential legal liabilities.
- VBNC Legionella: Hotels often face recurring Legionella infections despite negative lab results. This may indicate the presence of VBNC (Viable But Non-Culturable) Legionella, a dormant form undetectable by lab culture. Triggered by heat or shock treatments, it can quickly reinfect the system under favourable conditions.
- Traditional Testing Limitations: Conventional lab testing for Legionella can delay results by several weeks, allowing bacteria to proliferate unchecked. Hotels need faster, real-time solutions to mitigate risks effectively. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing the Legionella Risk in Hotels:
Regularly Test Outlets: Test all outlets frequently using a complimentary mix of testing solutions. Lab culture may be mandated but this method misses VBNC Legionella. PCR and/or rapid antigen tests will detect this dangerous form of the bacteria.
Conduct Routine Maintenance and Cleaning: Regularly clean and disinfect all plumbing components, including showerheads, taps, and spa facilities, to prevent biofilm buildup.
Flush Unoccupied Rooms: Implement a flushing schedule for unoccupied rooms to prevent water stagnation and ensure circulation in plumbing systems.
Maintain Proper Water Temperatures: Keep hot water above 60°C (140°F) and cold water below 20°C (68°F) to inhibit Legionella growth. Where temperature control is impractical, consider biocidal treatments.
Develop a Comprehensive Water Management Plan: Create a proactive water safety plan tailored to your hotel’s specific operations, including regular testing, preventive measures, and emergency response protocols.
Train Staff on Legionella Management: Educate maintenance teams and other staff on the importance of water system management, risks associated with Legionella, and proper testing and prevention techniques.
Utilise Rapid Testing Solutions: Traditional lab testing can delay results, increasing the risk of Legionella exposure in hotels. Hydrosense on-site Legionella testing provides results in just 25 minutes, allowing hotel staff to respond quickly, protect guests, and maintain a safe environment.
References
- https://www.mordorintelligence.com/industry-reports/hot-tub-market
- https://www.gminsights.com/industry-analysis/hot-tub-market#:~:text=Hot%20Tub%20Market%20size%20was,segment%20catering%20to%20luxury%20upgrades.&text=Growth%20Drivers:,Home%20improvement%20trend
- https://www.cidrap.umn.edu/legionella/cdc-traces-legionnaires-outbreaks-2-cruise-ships-hot-tubs
- https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1137470/full
- https://www.foxnews.com/health/legionnaires-disease-outbreak-linked-cruise-ship-hot-tubs-cdc-says
- https://cordis.europa.eu/project/id/604884/reporting#:~:text=On%20a%20global%20level%20there,million%20swimming%20pools%20(12%25)%20.
- https://www.aquawarehouse.co.uk/post/what-temperature-should-a-hot-tub-be
- http://www.hottubretailer.co.uk/2016/03/hot-tub-retailers-targeting-record-totals/
Legionella Risk in Cooling Towers
A cooling tower was the source for the discovery of Legionnaires’ disease. It was first identified in 1976, following a mysterious outbreak of pneumonia among attendees at an American Legion convention in Philadelphia. 221 people were infected and over 30 individuals died, sparking an intense investigation by the Centres for Disease Control and Prevention (CDC). This landmark discovery established the significant role of cooling towers in spreading Legionella.
Since then, cooling towers have remained a leading source of outbreaks of Legionnaires’ disease because Legionella can grow to outbreak levels within just 7 days.1
A survey of 196 US cooling towers revealed pathogenic Legionella strains in 27%.1
In 2014 on the outskirts of Lisbon, Portugal, an industrial wet cooling system was the source for one of the largest ever outbreaks recorded internationally – 403 cases were identified, of which 377 were confirmed. Sadly 14 people died.2
In New York in 2015, a cooling tower sickened 138 people and killed 16.3
Even Disneyland , California switched from fairytale to nightmare in 2017 where 22 cases of Legionnaires’ disease were linked to the park’s cooling towers.4
CDC research shows that from 196 cooling towers tested in the US in 2016, 84% of them returned a positive result for Legionella DNA, meaning the bacteria were either present or had been present in the system at some point.5
Water within cooling towers is heated via heat exchange, a process which creates ideal conditions for Legionella heat-loving bacteria to grow.
Factors Affecting Increased Legionella Risks in Cooling Towers:
- Generation of Aerosols: Because of their ability to spread Legionella over a wide area, cooling towers are regarded as one of the most dangerous and heavily regulated sectors in the water treatment and Legionella control industry. A study conducted in Norway found that Legionella bacteria could potentially spread more than 10 km from its source.6
- Biofilm accumulation: Cooling towers continuously wash the air as they operate, and because of this, they are constantly collecting debris, dirt and dust during the cooling process. Even if regular maintenance of the cooling tower is implemented properly, dust and debris will still enter and collect in the basin of the tower. Depending on where the cooling tower is located, the amount of material collecting in the water can be extensive and can contribute to the growth of biofilms that provide nutrients for Legionella to survive and grow.7
- Temperature: In many cooling towers, the sides are open, allowing sunlight to reach the cooling tower basin and encouraging algae to grow. It is important to protect the cooling tower basin (and the top deck of larger cooling towers) from sunlight as the temperature of the water in the system has a direct impact on the rate of Legionella growth.5
- Water quality: Make-up water usually comes from a municipal or well supply but can sometimes come from a holding tank, which can contain sludge, rust, and sediment. Less commonly used, surface water that comes from lakes, rivers, or reservoirs could be full of microorganisms and nutrients from the environment.
- Stagnant Water: Areas of stagnant water can prevent successful chemical treatment of the towers and allow Legionella and their hosts to flourish.7
- High Outbreak Potential: Cooling towers often serve large buildings and complexes, increasing the risk of widespread exposure if contamination occurs.
- VBNC Legionella Risks in Cooling Tower Management: Recurring Legionella issues in cooling towers, even with negative lab test results, may indicate the presence of VBNC (Viable But Non-Culturable) bacteria. These dormant bacteria evade detection by standard testing methods but can reactivate under favourable conditions, rapidly contaminating water systems. This poses a significant challenge for maintaining safe and Legionella-free cooling tower operations.
- Liability for Businesses: Inadequate Legionella management can result in legal and financial repercussions for businesses, alongside potential harm to public health.
- Limitations of Traditional Testing: Relying on conventional lab culture tests for cooling tower water monitoring can lead to significant delays, as results take 10–14 days and may produce false negatives. These tests will fail to detect viable-but-non-culturable (VBNC) bacteria. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing the Legionella Risk in Cooling Towers:
Regular Water Testing: Implement a routine water testing schedule to detect Legionella bacteria early. Testing should be frequent and follow industry guidelines. Don’t just rely on the lab culture testing method that can’t fully protect you.
Proper Water Treatment: Use appropriate biocides and water treatment methods to inhibit Legionella growth, ensuring the treatment plan is regularly reviewed and updated.
Maintain Optimal Temperature: Control water temperatures within cooling systems, as Legionella thrives between 20°C and 45°C. Keeping temperatures outside this range can reduce risk.
System Cleaning and Maintenance: Conduct regular inspections and cleanings to remove biofilm, scale, and sediment, which can harbour Legionella.
Monitor and Document: Keep accurate records of all maintenance activities, water testing results, and treatment applications to ensure compliance with regulations and support traceability.
Ensure Proper Design and Operation: Design cooling towers with water flow that minimises stagnation and keeps water well-circulated. Avoid conditions where water can stand for long periods.
Use Rapid Testing Technology: Consider innovative solutions like Hydrosense’s on-site Legionella test for cooling towers, which provides results in just 25 minutes. Fast results enable facility managers to make immediate decisions, helping prevent Legionella spread and protect the health and safety of building occupants and the public.
References
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6982084/#:~:text=Somewhat%20alarmingly%2C%20Legionella%20pneumophila%20was,diseases%20encountered%20in%20the%20winter
- https://www.elsevier.es/en-revista-revista-portuguesa-saude-publica-323-articulo-a-large-outbreak-legionnaires-disease-in-an-industrial-S0870902516300323
- https://wwwnc.cdc.gov/eid/article/23/11/17-0308_article
- https://legionellacontrol.com/legionella/legionnaires-disease-outbreaks-cooling-towers/
- https://www.ncbi.nlm.nih.gov/pubmed/29261791
- https://academic.oup.com/cid/article-abstract/46/1/61/338589?redirectedFrom=fulltext
Legionella Risk in Domestic Water Systems
Domestic water systems can harbour Legionella bacteria, which thrive in warm, stagnant water (20 – 45°C). Factors like biofilm buildup, scale, or poorly maintained systems create ideal conditions for bacterial growth. Legionella poses a significant health risk, as it can cause a serious pneumonia called Legionnaires’ disease or Pontiac fever, a milder flu-like illness. Infections occur when aerosolised water droplets, such as those from showers, taps, or hot tubs, are inhaled.
The responsibility for ensuring that water entering homes is free from Legionella typically falls on the water utility companies and local authorities. However, it’s important to note that Legionella can still grow within domestic water systems even if the incoming water meets the safety standards required.
When the water enters a home it becomes the homeowners responsibility for their own water systems. Likewise, landlords have a legal obligation to assess and manage Legionella risks in their rental properties.1
A 2019 study conducted in South Australia found that Legionella pneumophila was present in 64.2% of household showers.2
A UK study found 31% of household showers tested positive for Legionella.3
A 63-year-old man who passed away from Legionnaires’ disease is believed to have contracted the infection from his garden hose.4
Factors Affecting Increased Legionella Risks in Domestic Water Systems:
- Generation of Aerosols: Showers are a primary source of Legionella dispersal in domestic water systems. They create aerosols that can easily spread Legionella bacteria when inhaled. Unused showers (e.g., during holidays or between tenancies) allow biofilms to form, increasing the risk of bacterial growth and aerosol transmission.
- Biofilm accumulation: Water storage tanks and unused plumbing fixtures are prone to biofilm buildup, particularly on tank walls or in stagnant sections of pipes. These biofilms provide a safe environment for Legionella bacteria to survive, multiply, and reinfect water outlets like taps and showers.
- Temperature: Legionella thrives in water temperatures between 20°C and 45°C. Cold water systems are at risk if the temperature exceeds 20°C, which is especially common during warmer months or in poorly insulated systems. Hot water systems that fail to maintain temperatures above 55°C also present a significant risk.
- Occupancy Patterns: Premises with changing or irregular occupancy (e.g., rented, holiday homes or multi-occupant buildings) increase the likelihood of water stagnation, biofilm formation, and Legionella growth. Vulnerable populations, such as smokers, elderly individuals, and infants, are more susceptible to infection.
- Stagnant Water: Areas of stagnant water in the system, such as dead legs or unused fixtures, create an environment where Legionella can thrive. Stagnation prevents effective chemical disinfection and allows the bacteria to flourish.
- High-Risk Domestic Sources: Domestic systems such as hot tubs, swimming pools, garden hoses, sprinklers, pressure washers, air conditioning units, and humidifiers are potential Legionella sources due to their ability to create aerosols or harbour stagnant water.
- VBNC Legionella Risks – Recurring Legionella issues in domestic water systems, may indicate the presence of VBNC (Viable But Non-Culturable) These dormant bacteria evade detection by standard testing methods but can reactivate under favourable conditions, rapidly reinfecting showers, taps, and other water outlets.
- Traditional Testing Methods – Many people rely on traditional lab culture methods for Legionella testing. However, these methods may have limitations, potentially underestimating Legionella presence and delaying necessary actions to keep occupants safer. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing the Legionella Risk in Domestic Water Systems:
Regular Flushing of Water Systems: Ensure all taps, showers, and outlets are flushed regularly, especially after periods of low use, to prevent water stagnation.
Maintain Optimal Water Temperatures: Keep hot water systems above 55°C and cold water systems below 20°C to limit Legionella growth. Regularly check and adjust temperature settings if necessary.
Clean and Inspect Storage Tanks: Regularly clean and disinfect water storage tanks to remove sediment, biofilm, and debris. Ensure tank covers are secure to prevent contamination.
Reduce Stagnant Water: Minimise dead legs in plumbing, and disconnect unused pipework. Install systems to promote consistent water flow throughout the property.
Monitor Vulnerable Areas: Pay attention to high-risk areas, such as hot tubs, garden hoses, humidifiers, and pressure washers. Clean and disinfect these regularly.
Install and Maintain Filters: Consider using point-of-use filters on taps and showers to reduce bacterial exposure in high-risk settings.
Regular Water Testing: Conduct regular Legionella testing, using accurate and reliable testing methods that have the ability to detect VBNC Legionella.
Educate Occupants: Provide guidance to building occupants on reducing Legionella risks, such as ensuring regular water use and avoiding aerosols from stagnant water.
Use Professional Services: For complex systems, hire qualified Legionella risk management professionals to conduct regular inspections, maintenance, and compliance checks.
Use Rapid Testing Technology: Consider innovative solutions like Hydrosense’s rapid Legionella testing kits which are perfect for domestic water systems and provide results in as little as 25 minutes. Super easy to use, they enable homeowners or property managers to take immediate action to address contamination, preventing Legionella spread and safeguarding the health of residents and visitors.
Legionella Risk in Facilities Management
Legionnaires’ disease is a critical safety concern for building occupants, yet facilities managers often lack complete knowledge of Legionella control. Engaging expert third parties is key to maintaining safe water systems.
Facility management (FM) companies are directly responsible for ensuring the safety of their clients’ water systems. Failures in service quality can result in severe consequences, including substantial fines, legal liabilities, and irreversible reputational damage. To mitigate these risks, FM companies should adopt best practices in Legionella detection and management.
- Legionella pneumophila was detected in 53% (16/30) of office buildings sampled in a study.1
- 20% of office buildings tested positive specifically for Legionella pneumophila serogroup 1, which is the most common cause of Legionnaires’ disease.1
- The Centers for Medicare and Medicaid Services (CMS) building in Baltimore, Maryland was closed from early June to early August 2024 after Legionella bacteria were discovered in its water supply during renovations.2
- The Environmental Protection Agency (EPA) had to close three water fountains, one pantry sink, and two expansion tanks in the William Jefferson Clinton Federal Building in Washington, D.C.3
Factors Affecting Increased Legionella Risks in Facilities Management:
- Water Management Risks: Failure to adequately treat water systems with biocides or regularly monitor biocide levels can lead to bacterial resistance and rapid Legionella multiplication, increasing outbreak risks.
- Risk from Water Features: Fountains and decorative pools can aerosolise water, spreading Legionella if poorly maintained. Stagnation, organic debris, and inadequate treatment promote bacterial growth, posing risks to building occupants and visitors.
- System Design and Maintenance Challenges: Complex or outdated plumbing systems, particularly those with “dead legs” or redundant pipework, create prime conditions for Legionella. Biofilm, scale, and sludge buildup further exacerbate the issue.
- Aging Buildings: Older facilities or those undergoing renovations often have incomplete or inaccurate plumbing schematics, hindering effective risk assessment and monitoring of high-risk areas.
- Changing Water Usage Patterns: Adjustments in building usage over time can alter water flow, creating new high-risk zones not accounted for in the original design.
- Regulatory Non-Compliance: Failing to meet water safety regulations can result in legal penalties and diminished trust among clients and stakeholders.
- VBNC Legionella Risks in Facilities Management: Recurring Legionella issues in facilities, even with negative lab test results, may indicate the presence of VBNC (Viable But Non-Culturable) bacteria. These dormant bacteria are undetectable by standard methods but can reactivate and rapidly reinfect water systems, posing a significant challenge for effective Legionella control.
- Limitations of Traditional Testing: Reliance on conventional lab culture tests, which take 10 – 14 days for results and may produce false negatives or fail to detect viable-but-non-culturable (VBNC) bacteria, can delay remedial actions and heighten risks. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing the Legionella Risk in Facilities Management:
Adopt a Comprehensive Water Management Plan: Implement detailed plans that include preventive measures, routine monitoring, and emergency actions tailored to the facility’s specific risks.
Regularly Inspect and Maintain Plumbing Systems: Address dead legs, redundant pipework, and biofilm buildup through periodic inspections and maintenance.
Update System Documentation: Maintain accurate, up-to-date schematics for all water systems to identify and monitor high-risk areas effectively.
Monitor Water Usage Patterns: Adjust water management strategies to reflect changes in building use and ensure consistent water circulation.
Ensure Compliance with Regulations: Regularly review water safety policies and provide staff training to meet local and international standards.
Proactively Manage Risks in Older Buildings: Pay special attention to aging or renovated buildings, which are more likely to have system vulnerabilities.
Engage Expert Assistance: When necessary, collaborate with specialists to identify risks and implement advanced Legionella management strategies effectively.
Leverage Rapid Testing Technology: Facility managers can enhance Legionella control by using innovative solutions like Hydrosense’s on-site test. Delivering results in just 25 minutes, this rapid testing method empowers managers to take immediate action and test the efficacy of those actions in real time, minimising the risk of Legionella spread and ensuring the safety of building occupants and the public.
Legionella Risk in Marine Industry
Legionnaires’ disease poses a serious yet often overlooked threat in the marine industry. Ships, offshore platforms, and other marine vessels provide ideal conditions for Legionella bacteria to grow and spread, particularly within their self-contained water systems. The confined and communal nature of these environments amplifies the risk of outbreaks, making it critical for operators to implement robust Legionella management strategies.
Closed-loop water systems, reliance on desalinated water, and logistical challenges associated with testing and maintenance at sea further elevate the risks. High-traffic areas such as spas, showers, and HVAC systems are common sources of aerosolised Legionella, putting both passengers and crew at risk.
A study conducted between November 2022 and June 2024 identified 12 cases of Legionnaires’ disease among travellers on two cruise ships.1
On one cruise ship, Legionella pneumophila serogroup 1 (Lp1) and Lp2-14 were detected in all eight private balcony hot tubs tested.1
Legionella pneumophila serogroup 1 was found in 46% of non-passenger merchant vessels, putting the crew at risk.2
It’s predicted almost 40 million people will cruise annually by 2027 – passengers and crew will need protecting from the risk of Legionella.3
There have also been cases of shipyard fitters dying from Legionella after stripping down equipment such as pumps and being exposed to contaminated water.4
Factors Affecting Increased Legionella Risks Associated with Shipping:
- Design: Water systems on ships are often complex with difficult to access areas monitoring, maintenance and repairs. Older vessels may also contain plumbing materials that have degraded. Dead legs and blind ends are also a common problem on ships as they make monitoring and control even more challenging.
- Stagnant Water: Large capacity water tanks and extended water storage time may result in a low chlorine residual in the water. Low cabin occupancy can also result in water stagnation which encourages the formation of biofilms where Legionella grows.
- Water Storage: It is important that the source and quality of the water taken on board is known, although this may not always be possible in some countries. Conditions for storage of water on board ships are important, especially as they may be affected by temperature extremes when travelling in tropical regions. Higher temperatures encourage rapid Legionella growth.
- Difficult Access to the Lab: Testing water samples to ensure the safety of employees and the general public can be challenging on vessels. Access to the laboratory is usually limited and the reliability of the laboratories in various countries can be questionable at best. As a result, only using standard Legionella testing techniques onboard can be risky.
- VBNC Legionella: Persistent Legionella outbreaks on ships or offshore platforms, despite negative lab results, may point to the presence of VBNC (Viable but Non-Culturable) Legionella. These dormant bacteria are undetectable with standard testing methods but can reactivate when conditions are favourable, quickly contaminating water systems and endangering the health and safety of crew and passengers. Click Here to Find Out More About Limitations of the Lab Culture Test
Additionally, passengers and crew on ships are potentially at risk of exposure to Legionella bacteria in the same way as guests and staff in a hotel are at risk. Examples of sources include potable water, water for washing, showers and baths, spa pools, decorative fountains and others. Read more about the risk factors in hotels, and spa pools.
Tips for Managing Legionella Risk in the Marine Industry:
Recognise the Risks: Legionella poses a significant threat aboard ships, yachts, and offshore environments, where confined spaces and complex water systems heighten the risk of outbreaks. Train onboard personnel on the risks of Legionella and the importance of preventive measures.
Manage Potable Water Sources: Ensure proper sourcing, storage, and treatment of potable water supplies.
Create a Comprehensive Management Plan: A robust Legionella control plan should address all marine-specific risks, including routine Legionella testing, preventive measures, and emergency response protocols. This ensures safe water systems and reduces liability.
Remove Stagnation and Biofilm Risks: Stagnant water in rarely used pipes, unoccupied cabins, storage tanks, or “dead legs” in plumbing systems promotes Legionella growth. Conduct regular system flushing and remove unused sections of piping to maintain circulation. Check for biofilm formation in pipes and water systems and remove it.
Water Temperature Checks: Ensure water temperatures are outside the Legionella growth range. Keep cold water below 20°C and hot water above 60°C. Where temperature control is impractical, keep on top of alternative measures such as biocides.
Adopt Regular Testing: Regularly test potable water, HVAC systems, and all other water sources for Legionella, including hot tubs. Use a testing method that detects VBNC (Viable But Non-Culturable) Legionella, to avoid false negatives. Early detection allows for swift corrective actions and reduces the risk of outbreaks on board.
Leverage On-Site Testing Solutions: Relying only on traditional lab testing can result in delayed results and false negatives, a critical concern for vessels and remote offshore facilities.
Hydrosense’s on-the-spot Legionella test offers accurate results in just 25 minutes, delivering a clear Yes/No outcome. This rapid testing empowers crews to act quickly, and check the efficacy of remedial work, ensuring the safety and well-being of onboard personnel and passengers.
Legionella Risk in Car Washes
While not a primary source of Legionella infections, car washes still represent a significant potential risk due to aerosolisation of water during the washing process, which can spread the bacteria. These aerosols can infect human lungs and cause severe and potentially life-threatening infections like Legionnaires’ disease.
The relatively small but consistent proportion of infections linked to these settings highlights the importance of mitigation strategies.
- Over 8% of water samples from car washes in Italy were infected with Legionella pneumophila, 60% of these had levels between 200-1000 CFU/L.1
- In a 10 year study in the Netherlands of potential sources of Legionella infections, car washes/gasoline stations were implicated in 106 cases (3.5%). This means an average of 10 people per year were potentially infected by car washes during that period.2
- Aerosols generated by car washes can potentially travel long distances. One study suggests that Legionella can travel as far as 10 km in some cases, posing a potential threat to people in the surrounding area.3
Factors Affecting Increased Legionella Risks Associated with the Car Wash Industry:
- Temperature: Legionella bacteria require a temperature range of 20oC to 45oC and suitable nutrients, such as found in dirty water storage tanks, to flourish and multiply. It is therefore important to consider the temperature of the water used in a car wash.
- Stagnant Water: Less popular car washes may experience extended periods of stagnation, which, if combined with exposure to direct sunlight, can increase the risk of Legionella growth in water tanks and pipes significantly.
- Generation of Aerosols: Aerosols generated by car wash systems can travel long distances. The study of outbreaks of Legionnaires’ disease caused by long-distance spread suggests that in some cases Legionella can travel as far as 10 km. If aerosols created by a car wash are contaminated with Legionella, they can pose a threat to people in the area, not just users of the car wash.
- Water Quality: Water provided to car washes can sometimes come directly from the mains and may not be pre-treated. Moreover, some car washes have an additional problem of collecting wash water and recirculating it during further wash cycles. This process can increase the amount of general debris and nutrients in the water and can further support the growth of bacteria.
- The Potential for Contamination: In car washes, the presence of soaps, dirt, oils, and sediment, which provide nutrients to support microbial growth, creates a perfect environment for Legionella to multiply.
- VBNC (Viable But Non-Culturable) Legionella in Car Washes: VBNC Legionella, which are in a dormant state where they cannot be detected by standard culturing methods, pose a hidden risk in car washes. These bacteria can survive harsh environmental conditions, such as chemical treatments or nutrient deprivation, in water systems, and revert to an infectious state when favourable conditions return (e.g., warm temperatures or the presence of biofilm).
- Drawbacks of Conventional Testing: Traditional lab culture methods, which require 10 – 14 days for results, have many limitations which could produce false negatives, including missing the dangerous VBNC Legionella. These delays can hinder timely interventions and increase associated risks. Click Here to Find Out More About Limitations of the Lab Culture Test.
Tips for Managing Legionella Risk in the Car Wash Industry:
Develop a Comprehensive Water Management Plan: Create a detailed plan that addresses preventive maintenance, regular monitoring, and emergency protocols to mitigate Legionella risks in car wash systems.
Regularly Inspect Water Storage and Distribution Systems: Check water tanks, pipes, and spray nozzles for biofilm, sediment, and stagnant water. Address issues like unused pipework and areas prone to contamination.
Monitor Water Temperature: Ensure water temperatures remain outside the optimal growth range for Legionella (20°C – 45°C) to reduce bacterial proliferation.
Implement Recirculated Water Treatment: Treat recirculated water using filtration, UV disinfection, or chemical treatments to prevent the accumulation of nutrients and bacteria.
Conduct Routine Testing for Legionella: Regularly use rapid on-site testing methods to detect Legionella, including viable but non-culturable (VBNC) strains, for quicker and more reliable results.
Enhance Aerosol Control: Regularly maintain and clean spray nozzles and equipment to minimize the generation of aerosols, which can spread contaminated water droplets over long distances.
Train Staff in Water Safety Management: Educate workers on recognizing risks, maintaining hygiene, and following water safety protocols to ensure effective prevention measures are upheld.
Engage with Experts for High-Risk Systems: For older or complex car wash setups, collaborate with Legionella specialists to identify vulnerabilities and implement advanced control measures.
Ensure Compliance with Local Regulations: Stay updated on water safety guidelines and implement necessary measures to meet health and safety standards.
Use Rapid Testing Technology: Traditional lab testing often delays results, increasing potential risks. Rapid on-site Legionella tests, like Hydrosense, deliver results in just 25 minutes and can detect VBNC Legionella. These tests provide a clear Yes/No outcome, enabling car wash staff to act swiftly and make informed decisions to protect both workers and customers from potential exposure.
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