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Legionella bacteria may be a major concern for water systems, especially during the warmer months when conditions are just right for them to grow. These bacteria, which cause Legionnaires’ disease and Pontiac fever, thrive in man-made water systems and pose serious health risks when improperly managed. In this blog, we’ll explore why Legionella is more active in certain seasons and share some tips on how you can keep your water system safe.
Legionella bacteria occur naturally in freshwater sources, such as lakes and rivers, but are usually in concentrations too low to cause harm. However, when these bacteria get into man-made water systems, like plumbing, they can multiply to dangerous levels under certain conditions. Inhalation of contaminated water droplets can lead to a deadly form of pneumonia called Legionnaires’ disease. While not everyone exposed to Legionella will become sick, the potential for severe outbreaks are high in vulnerable populations such as older adults and those with weakened immune systems. For more details about Legionella and Legionnaires’ disease, check out this post.
Legionnaires’ disease cases often peak in summer and fall, from about May to November. This is because Legionella bacteria thrive in warm water, so these warmer times of year promote bacterial growth. There are several factors that can influence the risk of Legionella infection, especially during warmer seasons:
• Temperature: Legionella bacteria multiply rapidly in water temperatures between 20°C and 50°C (68°F to 122°F). In summer , plumbing systems, cooling towers, and other man-made water systems often fall within this ideal range.
• Water Stagnation: There is often reduced occupancy in buildings during warmer months. As a result, demand on water is lower, creating stagnant areas called “dead legs” where Legionella thrives.
• Cooling Systems and Air Conditioning: Cooling towers are a key component of air conditioning systems, and are often used in large buildings. These towers are prime spots for Legionella growth, and may release contaminated water droplets into the air, which can lead to outbreaks.
The Connecticut Department of Public Health has collated data from recent years to show this seasonality in Legionnaires’ cases, as seen in this graph:
The significant increase in Legionnaires’ incidence in warmer temperatures leads naturally to the question of how increased temperatures associated with climate change are predicted to impact disease prevalence. Legionella infections have been rising significantly over the past 20 years, and are predicted to continue to climb as global temperatures rise.
Furthermore, climate change is driving an increased frequency of extreme weather events, such as hurricanes, heavy rainfall, and floods. These events have a direct impact on urban water systems. For example, floodwaters can infiltrate normal water systems, carrying Legionella into these water systems and creating a stagnant, nutrient rich environment that is ideal for Legionella growth. Damaged water infrastructure leads to leakages and bursts, creating further opportunity for water contamination and exacerbating the problem.
Effective prevention and maintenance strategies are crucial for minimising the risk of Legionella contamination in large building water systems, particularly during peak seasons when the threat is heightened. Implementing a comprehensive approach that includes routine inspections, water temperature management, and system flushing can significantly reduce the likelihood of an outbreak.
1. Routine Inspections
Regular inspections are the cornerstone of a proactive Legionella prevention strategy, allowing for identification of potential problems before they escalate. Inspections should focus on areas where water can stagnate, such as storage tanks, cooling towers, and infrequently used fixtures. Any signs of corrosion, biofilm buildup, or sediment accumulation should be addressed immediately to prevent creating an environment conducive to Legionella growth.
2. Water Temperature Control
Maintaining water temperatures outside the optimal range for Legionella growth is another key preventive measure. Legionella bacteria thrive in water temperatures between 20°C and 50°C (68°F and 122°F), so keeping hot water above 60°C (140°F) and cold water below 20°C (68°F) can inhibit bacterial growth. It’s important to regularly monitor and adjust water temperatures, especially during seasonal changes when temperatures can fluctuate. For hot water systems, periodic thermal disinfection (raising the water temperature to 70°C or higher for short periods) can be an effective method to eliminate any Legionella that may be present.
3. System Flushing
Water stagnation and “dead legs” are common issues in large buildings, particularly during periods of low occupancy, such as over the summer months when many facilities experience reduced usage. Regularly flushing these areas helps to circulate fresh, treated water through the system, reducing the opportunity for bacteria to multiply. Flushing should be done at all points of use, including seldom-used outlets and sections of piping that are prone to stagnation. In addition, during periods of low occupancy, consider implementing a more frequent flushing schedule to ensure water remains in motion throughout the system.
By implementing these best practices, you can significantly reduce the risk of Legionella contamination, safeguarding your health and the integrity of the water system. Prevention and maintenance are ongoing processes that require vigilance and commitment, but the benefits of a well-maintained water system far outweigh the risks associated with Legionella outbreaks.
Recent outbreaks have highlighted the ongoing risk posed by Legionella bacteria:
London, Ontario (July 2024): A recent outbreak in London resulted in 25 confirmed cases, including one death, and 10 hospitalizations. All the infected people live or work within five kilometres of each other in south London. The Middlesex-London Health Unit found Legionella in three cooling towers in that area, highlighting the severe risks associated with an outbreak.
Melbourne, Australia (2024): Another outbreak in Melbourne linked multiple cases to a contaminated cooling tower in the western suburbs. This outbreak caused over 100 cases of Legionnaires’ disease, most of which required hospitalisation, and caused two deaths. This incident underlines the vulnerability of urban centers to Legionella outbreaks, especially during warmer seasons.
Legionella is a seasonal threat that needs careful management and proactive steps. Knowing when and where these bacteria are likely to grow, especially during the warmer months, is important to keep your water system safe. Regular monitoring, proper maintenance, and effective disinfection can go a long way in reducing the risk of Legionella contamination.
It's important to stay vigilant and informed, taking the necessary precautions to protect against this seasonal hazard. Now is the time to assess your water systems and ensure they are properly protected. Don’t wait for an outbreak—take action today to safeguard the health of everyone who relies on your water system.
