Legionnaires Disease : Legionella Bacteria

Legionella (legionnaires disease causing bacteria) are a species of bacteria that grow and live in water. These bacteria live in low numbers in natural water sources. But when they get into man-made water systems they can grow very quickly in high numbers.

Each of the below factors create the opportunity for the Legionella to increase in numbers. There are 2 types of diseases caused by Legionella bacteria. Pontiac fever and the most well known  Legionnaires disease.

Man-made systems often create an ideal environment for Legionella species to grow. Especially due to 3 factors:

  1. Water temperature
  2. Dirty water systems
  3. Stagnant water in pipes and storage tanks.

Legionnaires Disease

Legionnaires disease is an infection of the lungs that is a form of pneumonia. A person can develop Legionnaires disease by inhaling water mist contaminated withLegionella bacteria.

Legionella was discovered after an outbreak in 1976 among people who went to a Philadelphia convention of the American Legion. Those who were affected suffered from a type of pneumonia (lung infection) that later, the bacterium causing the illness was named Legionella pneumophilaThe disease then became known as Legionnaires disease.

The first identified cases of Pontiac fever occurred in 1968 in Pontiac, Michigan, among people who worked at the city’s health department. It wasn’t until Legionella was discovered after the 1976 outbreak in Philadelphia that public health officials were able to show that the same bacterium caused both diseases.

How do you get sick from Legionella?

  • Legionella enters the water system
  • Legionella has the opportunity to multiply to high numbers
  • An aerosol is created – droplets of airborne water with the Legionella bacteria
  • People breath the aerosols into their lungs
  • The Legionella bacteria infects the lungs and caused illness – Legionnaires disease
  • Infection of lungs – often mistaken for Pneumonia
  • Bad coughing, fevers – 15 – 30% mortality rate

Aerosols (water droplets) with high numbers of Legionella bacteria have to be breathed into the lungs to get sick.


Aerosol are created by spraying water, impacting water against a hard surface or by bubbling air through the water. You cannot get Legionnaires disease by drinking water. 

The warmer the water the more generally serious the illness – the bacteria are more virulent. The smaller the droplets the more generally serious the disease – get further into the lungs. The higher the numbers of Legionella bacteria, the greater the chance of illness. The longer the exposure the greater the chance of illness.

Who are most at risk?

  • Elderly
  • Smokers
  • Immune compromised
  • Pregnant moms

How do you prevent Legionella infections?

  • Keeping the water systems clean. Meaning lime-scale and dirt free. Removes the food that Legionella bacteria feed from.
  • These systems need to be kept in a good condition (rust free). This also minimises their food source.
  • Maintaining water temperatures below 25° C (77° F) for cold and above 52° C (125° F) for hot water at all times significantly reduces the risk of high numbers of bacteria.
  • Preventing water from stagnating. Keeping water flowing through the system means no time for growth.

Where are the areas of risk in a hotel?

  1. Cold water system – tanks, pipes, taps that carry the water. Can’t cool water, but can insulate/ separate hot/ cold pipes.
  2. Hot water system – geysers, tanks and pipes. Hot water reticulation system NB!!
  3. Dead ends, stagnant water tanks

Where are aerosols created?

  1. Shower heads
  2. Evaporative coolers/ cooling towers
  3. Jacuzzi’s
  4. Fountains
  5. Sprinklers
  6. Water misting coolers
  7. Swimming pools

Reducing the risk: A 15-point plan for reducing the risk from Legionella

The risk of Legionnaires’ disease can be minimised.

Follow the 15-point plan for reducing the risk from Legionella:

  1. Have one named person responsible for Legionella control.
  2. Ensure the named person has sufficient training and experience to be able to carry out the role competently and other staff are trained to be aware of the importance of their role in controlling Legionella.
  3. Keep hot water hot and circulating at all times: 50°C – 60°C (too hot to put hands into for more than a few seconds) throughout the entire hot water system. Water to reach > 52° C within 60 seconds.
  4. Keep cold water cold at all times. It should be maintained at temperatures below 20°C throughout the system to all outlets (this may not be possible when the ambient temperature is high, but every effort should be made to ensure that cold water entering the premises and in storage remains as cold as possible). 25°C is absolute max!
  5. Run all taps and showers in guest rooms and other areas for several minutes to draw through water (until it reaches the temperatures stated in points 3 and 4) at least once a week if rooms are unoccupied, and always prior to occupation.
  6. Keep shower heads and taps clean and free from scale.
  7. Clean and disinfect cooling towers and associated pipes used in air conditioning systems regularly – at least twice per year.
  8. Clean, drain and disinfect water heaters (calorifiers) once per year.
  9. Disinfect the hot water system with high level (50mg/l) chlorine for 2–4 hours after work on the system and water heaters and before the beginning of every season.
  10. Clean and disinfect all water filters regularly, as directed by the manufacturer, at least every one to three months.
  11. Inspect water storage tanks, cooling towers and visible pipe work monthly. Ensure that all coverings are intact and firmly in place.
  12. Inspect the inside of cold water tanks at least once per year and disinfect with 50mg/l chlorine and clean if containing a deposit or otherwise dirty.
  13. Ensure that when carrying out system modifications or new installations they do not create pipework with intermittent or no water flow, and disinfect the system following any work.
  14. If there is a spa pool (also known as whirlpool spas, ‘Jacuzzis’, spa baths), ensure that:
    1. it is continuously treated with 2–3mg/l chlorine or bromine and the levels and pH are monitored at least three times per day;
    2. at least half of the water is replaced each day;
    3. sand filters are backwashed daily;
    4. the whole system is cleaned and disinfected once per week.
  15. Keep daily records of all water treatment readings, such as temperature, pH and chlorine concentrations and ensure they are checked regularly by the manager.

Microbiological Risk

Infection levels occur at much higher bacterial loads. The below table shows the relative risk for Legionella exposure

Further advice about specific controls should be sought from experts in this field. They can carry out a full risk assessment of the accommodation. Your local public health authorities can advise you further.

Learn More About Legionella

chemistry testing
Sensory evaluations

Logged in as Adrian Carter. Log out »


Hygiene Survey Manager

Related Posts