Legionella is a genus of bacteria that causes a type of severe pneumonia called Legionnaires’ disease and a mild respiratory disease called Pontiac fever. According to the World Health Organizaion (WHO), Legionnaires’ disease has an overall death rate of 5 to 10%, but it can be as high as 40 to 80% in untreated immuno-suppressed patients.
Epidemiological statistics by Public Health England show that Legionnaires’ disease affects around 300 people in England and Wales every year. It typically emerges in the form of an outbreak from contaminated water sources, but the path this pathogen takes to end up in our lungs is nothing short of fascinating.
The Odds Are Against Legionella
Legionella bacteria are present in small concentrations in natural sources of water, such as lakes, rivers and groundwater. They live inside other single-celled organisms like amoeba and in biofilms attached to surfaces.
To cause Legionnaires’ disease, Legionella have to enter our lungs and infect a type of white cells called alveolar macrophages that look similar to amoeba.
It seems very unlikely for Legionella, a scarce aquatic bacteria that doesn’t primarily target humans, to enter our lungs. Additionally, Legionnaires’ disease doesn’t transmit from person to person. Still, artificial water systems can sometimes meet just the right conditions for Legionella to directly infect a large number of people and cause an outbreak.
So How Does it Infect You?
In order for Legionella to become a health risk, artificial water systems must have the right conditions for Legionella to grow in. There must also be a way for the contaminated water to mix with air where it can be inhaled. Here’s how artificial water systems can enable Legionella to infect you.
Step 1: Growth
Legionella is present in small concentrations in water sourced from natural sources. When the ideal conditions for legionella are met, they can grow to potentially harmful levels.
Ideal conditions for Legionella growth in artificial water systems include:
- Water temperatures between 20℃ to 45℃
- Stagnation
- Nutrients such as rust and organic matter
- Low concentration of disinfectants
Step 2: Aerosolisation
Water contaminated with legionella must be aerosolised or mixed with air to cause infection. This can be anything that creates water droplets or mist, such as humidifiers, hot tubs, water fountains and even water taps.
Step 3: Inhalation
Inhaling airborne water droplets containing legionella can lead to infection. If the contaminated airborne water droplets spread into a large area, many people can get infected, leading to an outbreak. Water systems that create water droplets as a part of the process are among the most common sources of legionella exposure.
How Common Sources of Legionella Exposure Act As Perfect Pathways
Evaporative Cooling Towers
Evaporative cooling towers are a general term for devices that use the evaporation of water for cooling purposes. They’re commonly used in industrial applications and in large buildings. If the water being used is contaminated, the resulting stream and mist can be dangerous to those who may inhale it.
Hot Tubs
Jets and air blowers in hot tubs are constantly making water droplets and mist. The warm temperature of water in hot tubs is ideal for legionella growth. Hot tubs also constantly recirculate the same water instead of draining the water after each use.
Although hot tubs automatically remove contaminants and add disinfectants to the water, disinfectant is also rapidly lost due to high temperatures. If not maintained properly, hot tubs can support legionella growth, aerosolise the contaminated water and infect the people in and around the spa.
Water Stagnation
Hot and cold water systems in large buildings can have areas of stagnated water where legionella can grow. For instance, if a tap isn’t used for some time, water may stay stagnant in the corresponding plumbing and lead to biofilms with legionella. When the tap is eventually used, these biofilms may come off in chunks and cause infection.
Controlling Legionella Risk
Raising Legionella Awareness
Those responsible for building maintenance, especially in facilities with complex water systems like hotels, hospitals and schools, must understand the dangers posed by Legionella. Regular training sessions and updates on Legionella prevention should be mandatory.
Under the UK health and safety legislation, employers and building managers must follow guidelines to protect residents and employees from legionella exposure. There are legionella training programmes those in charge can take to minimise legionella risk.
Identifying and Controlling Legionella Risk
Identifying potential Legionella hazards involves a thorough inspection of all water systems within a building. Areas prone to stagnant water, such as unused pipes or rarely used taps, must be regularly inspected.
Controlling these risks involves setting up a strict regimen of cleaning and maintenance. This includes ensuring that water temperatures are either hot enough to kill bacteria or cold enough to inhibit bacterial growth, typically above 50°C for hot water and below 20°C for cold water.
Additionally, physical cleaning and chemical treatment of water systems can prevent the formation of biofilms, where legionella bacteria thrive.
Conducting Regular Risk Assessments
A comprehensive Legionella risk assessment should be carried out initially and regularly thereafter, especially after any changes in the water system or its use. This assessment will help identify specific areas of risk and the effectiveness of the existing control measures.
The risk assessment process should involve checking all aspects of the water system, from its entry point to taps and showers, and should include testing water temperatures and sampling for Legionella. There are also experienced professionals who provide legionella risk assessment services.
Appointing a Responsible Person
Someone with sufficient authority and knowledge should be appointed to ensure legionella safety in a residential building or workplace. This person, who could be an internal employee or an external expert, is tasked with overseeing the implementation of Legionella control measures.
The responsible person must ensure that the control strategies are executed correctly and that staff are trained appropriately. In larger facilities, it might be necessary to have a team of people sharing these responsibilities to cover all aspects of water system management comprehensively.
