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Legionnaires Disease. What is it?

Legionnaires Disease

What is Legionnaires Disease?

Legionnaires disease and how to protect against it.


The history of Legionnaires disease

The bacterium got its name after a 1976 outbreak, when many people who went to a Philadelphia convention of the American Legion suffered from this disease, a type of pneumonia (lung infection). Although this type of bacterium was around before 1976, more illness from Legionnaires' disease is being detected now.


Symptoms of Legionnaires disease

Legionnaires' disease can have symptoms like many other forms of pneumonia, so it can be hard to diagnose at first. Signs of Legionnaires' disease can include:

  • Cough
  • Shortness of breath
  • High fever
  • Muscle aches
  • Headaches

These symptoms usually begin 2 to 14 days after being exposed to the bacteria.

What is Legionella?

It is a respiratory infection which is fatal in 15-20% of cases, caused by Legionella bacteria.

The people most at risk are elderly smokers, people with respiratory problems or those with weakened immune systems. Legionella bacteria develop in the warm water found in pipework and central heating systems, but only become dangerous when they are inhaled in aerosol format, as particles suspended in water droplets. They spread into the lungs, and are absorbed by the immune system, and rapidly develop in white blood cells. Legionella is treated by antibiotics (Macrolide).

The World Health Organisation (WHO) cite the risk levels as 1,000 CFU* Legionella per litre of water (50 for hospitals).

*CFU: Colony Forming Units

Which plumbing installations are at risk from Legionella?

The installations most at risk are those which provide the ideal environment for Legionella to develop i.e. stagnant water between 20-46C, with a peak temperature between 30-37C, and deposits such as scale, rust, mud, etc.)

The alert level to undertake treatment is 1,000 CFU of Legionella pneumophilia / litre of water.

For high risk patients (with suppressed immune systems) in the hospital environment, the concentration level for Legionella will be maintained beneath the alert level at draw-off points, to secure the points-of-use (independent and instant production of hot water, 2 micron terminal microfilters, etc.).

Most curative treatments are ineffective

- Chemical shock: chlorine injection ! 10 mg/litre for 8 hours.

- Thermal shock: circulating hot water at 70C for 30 minutes.

1. These treatments only have a short term effect:

The system can be very quickly recolonised within 3-4 weeks.

In corroded storage tanks and installation dead-legs Legionella bacteria can develop in the scale and biofilm, finding a refuge which helps them to resist temperature changes and bactericidal disinfectant solutions.

Following a curative treatment, there is a risk that the biofilm will be released into the system, allowing Legionella bacteria to colonise new areas.

2. They can have a detrimental effect on the distribution and drainage system

which are subject to extreme conditions. The system must be able to withstand thermal expansion, high temperatures and the chemicals used for treatments.

(For example: damage caused by a PE sleeve joint becoming detached between the floor trap and a shower tray manifold, following a disinfection at 70C.)

3. There are significant risks to users when the treatments are taking place:

- the risk of 3rd degree burns during thermal shocks.

- the risk of poisoning during the chemical shock treatment.

4. These operations are costly and difficult to undertake fully at all points in the system

(various deposits, dead-legs, heat loss, etc.) requiring the water supply to be out-of-service.

Thermostatic mixing valves aid in prevention of the Legionella bacteria

Legionella bacteria are destroyed above 60C and cannot multiply above 47C. The solution is to generate and store hot water at temperatures above 60C and to safely reduce the water temperature at the point of outlet by utilising a thermostatic valve (TMV) - see the Code of Practice and Guidance Document L8 of the HSE. Therefore thermostatic mixing valves should be installed as close as possible to the discharge points to reduce the risk of water standing open at an 'at risk' temperature.




How to prevent Legionnaires disease.