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  • > Legionellosis: prevention is better than cure

Legionellosis: prevention is better than cure

June 2013

The methods of eliminating Legionella in healthcare facilities are ineffective in the long term. Monitoring and implementing preventative tools provide the best solution for protecting hot water systems against the risk of contamination by Legionella.

One of the bacteria found in the water system, Legionella, and more specifically Legionella pneumophila, is subject to routine microbiological monitoring. It is responsible for respiratory infections that are fatal in 15-20% of all cases. When present, this pathogen is found in the biofilm that forms naturally in water controls and the pipe work. Bacterial aggregates can easily detach during the passage of water, and pass suspended in aerosol format when a shower or tap is turned on. They are then inhaled by the user at the point-of-use, especially during showering. Installations which contain deposits (scale, rust, sludge, etc.) with standing water between 20 and 46°C are most at risk.

Monitoring Requirements

For example, in France, since 1st January, 2012, all Institutions Receiving the Public (IRP) are required to monitor the bacteriological quality of the water. A directive of 1st February, 2010 defines the procedure for measuring the temperature of the water and the search for Legionella in all hot water systems. The alert level triggering the implementation of measures is 1,000 CFU (Colony Forming Units) of Legionella pneumophila / litre of water. Similar protocols are in place in most European countries. 

The Health and Safety Executive (HSE) L8 Approved Code of Practice and Guidance* requires the bacteriological quality of water to be monitored in sanitary installations in buildings where the Health and Safety at Work Act 1974 applies. This identifies the procedure for measuring the temperature of the water and the search for Legionella in all water systems. The alert level triggering the implementation of measures is between 100 and 1,000 CFU (Colony Forming Units) of Legionella pneumophila / litre of water. Similar protocols are in place in most European countries.

These protocols advocate prevention. For example, they require water to be circulated at minimum temperatures to reduce the risk of Legionella developing, and they also recommend maximum temperatures to reduce the risk of scalding. In the UK, the L8 ACOP recommends that hot water should be stored at 60°C and distributed so that it reaches a temperature of 50°C within one minute at outlets. It also states that: “Where a significant scalding risk has been identified, the use of TMVs on baths and showers should be considered’’ to reduce the temperature to safe levels in line with the Building Regulations 2010 guidelines.** Final distribution pipes from the thermostatic mixing valves to the point-of-use must be as short as practically possible, and in high risk applications not more than 2 metres. In low risk applications, the maximum length is 5 metres, with water discharged within 30 seconds.

Ineffective treatment

Where Legionella has been identified, curative treatments, whether chemical or physical, are relatively ineffective in the long term and create potential ‘collateral damage’. Injecting chlorine (≥10 mg/litre for 8 hours) or circulating very hot water (at 70°C for 30 minutes) can only have a limited effect if a corroded tank or a dead leg serves as a refuge for Legionella. The system can be re-colonised within 3 to 4 weeks and the bacteria may even spread to other parts of the system.

The pipe work and connection points in the distribution and drainage systems do not easily withstand chemical or thermal shock treatments. Furthermore, it is difficult to ensure that the entire network has been properly treated. The user also risks serious scalding or chlorine poisoning if they accidentally use an installation that has not been correctly isolated while the treatment takes place.

Treating the Source of the Risk

Various precautions mean that there is no need to resort to these treatments, or at least their frequency can be reduced. Creating a circulating loop will ensure that water can be circulated at more than 50°C in the system. Final distribution pipes to the outlet should be as short as possible: 5 metres in low risk environments and 2 metres in high risk environments.

To avoid any risk of scalding, and to offer the user greater comfort, we recommend a thermostatic mixing valve certified to TMV3***. If the cold water suddenly fails, the hot water is instantly shut-off. 

Additional safety measures can be provided at the outlet via auto-draining devices such as Delabie’s Tonic Jet and Round shower heads, which drain any remaining water after each use. Similarly, Premix electronic shower panels achieve the same result, by automatically purging for 40 seconds after 24 hours of inactivity. This duty flush is standard with all Delabie branded electronic controls.

Finally, in Autumn 2013, Delabie will launch a Biofil cartridge with an integrated filter, sterilising grade 1 µm, which is suitable for fitting to shower heads or hand sprays. Lasting for 62 days, these filters will ensure that any bacteria in the water system are filtered out.

 

* The Health and Safety Executive L8 Approved Code of Practice and Guidance: Legionnaire’s disease: The control of legionella bacteria in water systems (2004)
** HM Government Building Regulations 2010 Part G: Sanitation, hot water safety and water efficiency
*** NHS Estate D08 approved