ADVICE & OPINION
COMPLIANCE
In association with LEGIONELLA TESTING
The LCA requires its members to have in place
management procedures and appropriately
competent sta , that give them the capability of
responding appropriately to positive legionella
results. Positive legionella results following
sampling are one area where it’s possible to
misinterpret the meaning and end up with what
could at best be inappropriate expense and at
worst, a dangerous situation and risk to life.
SAMPLE PLANNING
Interpretation of results starts with a suitable
sample plan. Samples can be taken pre or post flush
and with or without disinfection of the outlet. The
selection of location, type of sample and method of
analysis chosen forms part of the sample plan.
The first priority should be to consider measures
to eliminate or reduce the risk before designing
monitoring measures. Where it is impossible or
not reasonably practicable to reduce the risk and
the risk assessment recommends monitoring for
the presence of legionella by sampling, there are
a number of factors to consider in a sample plan;
including:
How o en should samples be taken?
Legionella is relatively slow growing but may
develop to hazardous levels within days or weeks
in ideal conditions
The HSE guidance in HSG274 Part 2 details weekly
samples for legionella where controls, such as
temperature or biocide, are not being consistently
achieved
Where should samples be taken?
Samples should be checking areas where
legionella is likely to grow – deadlegs, underused
outlets, areas where controls have failed or areas
where risk is identified for some other reason
How should samples be taken?
For systems otherwise under control this method
should generally be pre-flush without disinfection
to examine the risk that exists to the users of the
system from the outlets
In some cases, it would also be appropriate to
sample post-flush, with disinfection of the outlet
to examine how the system is performing as a
whole
There is limited value in sampling post-flush
downstream of mixing valves or sampling postflush
without disinfecting the outlet although
sometimes this is useful in investigation work
14 JULY 2021
CONFIRMING A POSITIVE RESULT
Positive legionella results occur in around 10–20
per cent of laboratory water samples, which take 10
days to complete and may take a further two days
to confirm with traditional confirmation techniques.
The laboratory will normally send a positive
notification once the result is confirmed.
The LCA would expect that any registered member
would have a procedure to notify their client, log the
result, track actions, note resolution and close out a
positive legionella result.
The result should be notified to a client at the
earliest opportunity, and this includes interim
positive results. HTM0401 Part B gives good advice
on how to interpret positive legionella results
in healthcare settings. For other settings the
general principles are the same, but the
susceptibility of the population is likely
to be lower.
The interpretation of sample
results will follow directly
from a well-designed sample
plan. A sample is a small part
designed to represent a larger
population. In this case you’ve
selected small volumes of water to
represent the risk in the water system
as a whole. When addressing issues, you
must consider the whole system and not just the
sample locations if the results indicate widespread
contamination.
CLIENT INFORMATION
An LCA Member’s procedure should detail how they
tell their client the information and how they arrive
at the advice they give. This procedure should then
be followed in practice and at audit the LCA will
expect to see an audit trail for each positive result.
For legionella to grow there must be suitable
conditions and there will be a root cause for these
conditions. Actions following positive samples
must address the root cause rather than just the
symptom. Common factors include:
Stagnation, areas being less used than previously
thought
Thermal gain/loss, meaning systems normally
reside at growth temperature despite running
below 20 degrees a“ er two minutes or above 50
degrees within one minute
Stagnation due to failed HWS circulation
Unknown deadlegs
Materials or contamination in the system that
support growth
Reviewing the assessment of the risk and
addressing whatever is found must be the primary
recommendation but unless very simple and
straightforward to achieve, there should also be
interim recommendations.
Recommended actions should be appropriate for
the results. This can be a di— icult balance to strike
but if the results indicate limited localised issues,
take limited localised action, if results indicate more
widespread issues, take system level actions.
LOGGING A POSITIVE LEGIONELLA RESULT
The result should be logged on systems as a nonconformance
like any other loss of control
non-conformance. Your interpretation,
recommended actions and the
reasons behind these should also
be logged and recorded as part of
the process.
TRACKING A POSITIVE RESULT
Once the result has been logged
in a system the consequent actions
need to be tracked and auditable.
If actions are required by you or your
customer then ensure these are completed and
recorded in your logging process.
RESOLVE THE POSITIVE RESULT AND CLOSE OUT
Once the root cause has been identified and
resolved this action should be noted on a LCA’s
member’s log and the positive result closed out.
In many cases it is normal to carry out follow up
sampling a“ er remedial action to verify success.
SUMMARY
Sampling for legionella can be an important
part of the monitoring of control measures in a
written scheme and competent interpretation of
positive results is essential. Appropriate planning,
technique and interpretation is vital to ensure the
information obtained by sampling is valid and
useful. The LCA requires members to have in place
management procedures that detail how samples
are planned, carried out, non-conformances logged
and dealt with and actions closed out including
communication with their clients.
The Legionella Control Association offers advice on the factors its
members should consider when interpreting and reporting positive
legionella results when a sampling plan is being followed