Chapter 7
What happens if the result is Positive?
Getting a positive count for legionella bacteria is quite common so it is important that there is a plan
to deal with these circumstances.
This plan should be set out in the “Written Scheme of Control”. A Legionella written scheme of control is a comprehensive risk management document identifying the measures required to control your water systems. It is compiled following the legionella risk assessment.
If these documents are not available, you will need to do two things:
- Implement an immediate plan to eradicate or minimise the legionella in your water system.
- Make arrangements for the assessment and written scheme to be undertaken by specialists.
What is the risk to people who work/visit your property?
| What is the risk to health? | Typical risk to an AVERAGE HEALTHY person | How many legionella are there? | |||||||||
| Less than 10 |
10 to 100 |
100 to 1000 |
1,000 to 5,000 |
5,000 to 10,000 |
More |
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| What strain of legionella is it? | Legionella pneumophila sg 1 | LOW | LOW-MED | MEDIUM | HIGH | VERY HIGH | |||||
| Legionella pneumophila sg 2-15 | LOW | LOW | LOW-MED | MEDIUM | HIGH | VERY HIGH | |||||
| Legionella species | LOW | LOW | LOW | LOW-MED | HIGH | VERY HIGH | |||||
| Risk Groups |
People are also HIGH RISK if their underlying health conditions include … Immunosuppression, long term respiratory diseases, liver and kidney diseases as well as tobacco smoking. Consequently, even low levels of legionella can be fatal for elderly people who also have underlying health conditions. |
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Age …….. Health … |
85% of all deaths are for people aged 50+ 75% of all deaths are for people with an underlying health condition |
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What immediate measures are effective
Minimising AerosolsTo contract Legionnaires’ Disease, the bacteria need to get into our lungs. The legionella bacteria need to be in an aerosol and then to be breathed in, once they reach our lungs they are able to proliferate rapidly and produce a pneumonia type illness. |
What Causes Aerosols? Items which create fine sprays include:- |
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| ACTIONS Take showers and baths out of service, keep toilet lids closed when flushing. | |
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Removing Bacteria from the Aerosols If showers and baths are critical to keeping the property open and need to be kept in normal operation, then consider installing “point of use” filters. These are specialist filters which are so fine that they can trap the legionella bacteria. They have a life-span of 30-150 days and can reduce the usual flow rates a little. Fitting them can take as little as 60 seconds per outlet. |
What are these Filters? There are two general types:-
ACTIONS Order these filters in advance so that they are available to be |
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Killing the Bacteria Legionella can be killed by heat, so getting the hot water temperatures above 60°C is a cheap and effective method. Simply raise the thermostat on your calorifier/hot water cylinder to 65°-70°C and run each outlet in turn. Display scald warning signs! The pipework/outlets downstream of Thermostatic Mixer Valves (TMVs) will never attain these higher temperatures. |
Chemical Disinfectants Disinfectants can be used to sanitise a single outlet or the entire water system. Using chemicals is the most common method to kill legionella in TMVs and the outlets they protect. These are highly effective but sometimes more than a single disinfection is required. |
| Raising the hot water temperature throughout the entire property can normally be done in-house and undertaken immediately by your own staff. This won’t kill all the legionella but should reduce their concentration whilst you schedule a specialist to chemically disinfect all the water services. |
Which type of disinfectant is best? Silver Hydrogen Peroxide – This can be left in the water system for many hours as it has no taste or odour (and is safe to do so). It’s good at breaking up biofilm and reasonably good at killing legionella. Chlorine – This is less good at removing biofilms but much better at killing legionella. Unfortunately, staff and residents cannot wash or drink the water during a chlorine disinfection process. |