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Methods for the Examination of Waters and Associated Materials |
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1.1 Aims
Legionnaires’ disease was first recognised in July 1976 and the bacterium later isolated and named Legionella pneumophila (1).Since then, over 45 other species of Legionella have been described of which at least 18 have been associated with disease in humans.
- These organisms are widespread in the natural aquatic environment and in artificial water systems.
- The organism is an opportunistic human pathogen and infection is more often associated with artificial water systems.
The disease is not known to be transmissible via person-to-person contact. As a result, the way to prevent or control outbreaks of Legionnaires’ disease is to inhibit or limit the growth of these organisms in water.
In the UK, the control of legionellae (bacteria of the genus Legionella) is prescribed in legislation (2) and associated regulations (3).
- A code of practice and associated guidance were first published as separate documents and were revised and combined into one document in 2000 (4).
- In 1992, a British Standard (5) on Legionella sampling was published, and in 1998, an international standard (6) (which is currently under revision) for the detection and enumeration of legionellae by culture was published.
- These publications were produced as a result of concerns arising from a number of outbreaks occurring within the UK and elsewhere.
An increasing requirement to ensure that measures to control legionellae are effective has demonstrated the need for guidance on sampling for the presence of Legionella in water distribution systems.
However, investigations of outbreaks and the results from quality assessment schemes have shown that there is appreciable variation both in terms of the procedures followed for the routine sampling of systems, and the processing of the resulting specimens.
The procedures described in the British Standard (5), whilst appropriate for the investigation of the origin of colonisation within a system, are impractical for routine monitoring purposes assessing the effectiveness of control measures, or for rapid screening of the many systems that may need to be sampled in outbreak investigations.
- Increasingly, in hot water systems various control procedures, such as the use of copper and silver ionisation or chlorine dioxide, are being applied to the control of legionellae.
- This applies particularly to situations where control by maintaining recommended temperature regimes is not possible, and as a consequence, these systems often require sampling (4).
There is also a need for guidance on sampling in the event of outbreak investigations.
It is, therefore, the aim of this document to bring together information on likely sources of Legionnaires’ disease, and the selection of sampling sites, sample procedures and analytical techniques.
Although it is necessary to cover some aspects of risk assessment in order to facilitate the selection of sampling sites, it is not the intention to give extensive explanations of how to carry out a risk assessment, as this is covered elsewhere (7).
- However, a risk assessment should be conducted before any sampling of a water system is undertaken.
| Format adapted by T2 Scientific© 2005 |
t2.200.1.v1.0 |
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Source: Blue Book 200 Part 1 downloaded 27 May 2005 |