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Legionella Sampling & Monitoring
- All Legionella monitoring
programmes should include routine sampling and testing
for the presence of bacteria, both general (aerobic)
bacterial species and Legionella bacteria. Since the
detection of Legionella bacteria requires specialist
laboratory techniques, routine monitoring for aerobic
bacteria can be used as an indication of whether microbiological
control is being achieved.
Recommended Frequency of Sampling
In addition to the regular sampling for aerobic bacteria,
a routine monitoring scheme should also include periodic
sampling for the presence of Legionella bacteria. This
should be undertaken at least quarterly,
unless sampling is necessary for other reasons, such
as to help identify possible sources of the bacteria
during outbreaks of Legionnaires’ disease. More
frequent sampling should be carried out
when commissioning a system and establishing a treatment
programme. Sampling should be carried out, on a
monthly basis, until it can be shown
that the system is under control.
Legionella Positive Sample
If a Legionella-positive sample is found as a result
of routine sampling, more frequent samples may be required
as part of the review of the system/risk assessment,
to help establish when the system is back under control.
In the UK the Health & Safety Executive recommend
that the sampling method should be in accordance with
ISO 11731:19988 and the biocide neutralised where possible.
Samples should be taken as near to the heat source as
possible. They should be tested by a UKAS accredited
laboratory that takes part in the Public Health Laboratory
Service Water Microbiology External Quality Assessment
Scheme for the isolation of Legionella from water. The
laboratory should also apply a minimum theoretical mathematical
detection limit of less than, or equal to, 100 Legionella
bacteria per litre of sample.
Interpretation of Results
Legionella bacteria are commonly found in almost all
natural water sources, so sampling of water systems
and services may often yield positive results and the
interpretation of any results of sampling should be
carried out by experienced microbiologists. Failure
to detect Legionella bacteria should not lead to the
relaxation of control measures and monitoring. Neither
should monitoring for the presence of Legionella bacteria
in a cooling system be used as a substitute in any way
for vigilance with control strategies and those measures
identified in the risk assessment.
Specialist Laboratory Services
Legionella Control International offer a comprehensive
range of UKAS accredited Legionella testing, sampling
and microbiological laboratory analysis services capable
of undertaking an extensive range of analyses including
those for Legionella, E.coli O157, Pseudomonas, Norwalk
virus and others.
Our professional lab services can also be used for
the testing and microbiological analysis of samples
to assist in the identification of food poisoning bacteria
including Salmonella, Listeria, E.coli O157, Campylobacter
and Clostridium perfringens.
Additional Information
For further information and expert assistance please
call us on +44 (0) 161 877
0586 or email info@legionellacontrol.com.
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