1. Legionella
Sampling
Culture v PCR
- By Nemco Utilities
(www.nemco-utilities.co.uk)

2. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
The gold standard for Legionella testing has always
been the culture method (often referred to as the
standard reference method) whereby the bacteria are
filtered from a water sample, grown and then the
number of colony forming units (cfu) estimated.
However, this is a labour intensive process with a 12 day
turnaround. Given the penalties for non-compliance
and costs associated with taking water services out of
use for 12 days, the culture method is rapidly becoming
outdated.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

3. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
A number of recent scientific advances have
revolutionised the face of Legionella analysis and now,
with a decent courier, samples can be turned around in
24 hours (4 in an emergency). Progress has been made
possible due to the use of Polymerase Chain Reaction
(PCR) technology. Rather than actually growing the
Legionella bacteria, PCR works by isolating fragments of
DNA from the water sample and amplifying them to a
detectable level. This process is a lot quicker, more
efficient and can largely be automated.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

4. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
PCR has been of inestimable value especially for trend
analysis and when investigating outbreaks. It is not
without its problems. The initial stumbling block was that
of detecting ‘dead’ or ‘non viable’ cells, that would not
show up on culture. This has since been largely
overcome, but PCR in general terms still returns far more
positive results than the culture method. This leads on to
the next problem of reporting units and their correlation
with action levels.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

5. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
The current Legionella guidance ACOP L8 contains
recommendations for ‘Action in the event of a positive
sample’ as below (for domestic water systems):
Legionella bacteria (cfu/ ACTION REQUIRED (L8)
litre)
More than 100 but less than Details >>
1000
More Than 1000 Details >>
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

6. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
Legionella bacteria (cfu/ litre) ACTION REQUIRED (L8)
More than 100 but less than Either:
1000 (a) If only one or two samples
are positive, system should be
re-sampled. If a similar count is
found again, a review of the
control measures and risk
assessment should be carried
out to identify any remedial
actions.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

7. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
Legionella bacteria (cfu/ litre) ACTION REQUIRED (L8)
More than 100 but less than (b) If the majority of samples
1000 are positive, the system may
be colonised, albeit at a low
level, with legionella.
Disinfection of the system
should be considered but an
immediate review of control
measures and risk assessment
should be carried out to
identify any other remedial
action required.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

8. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
Legionella bacteria (cfu/ litre) ACTION REQUIRED (L8)
More than 1000 The system should be re-
sampled and an immediate
review of the control measures
and risk assessment carried
out to identify any remedial
actions, including possible
disinfection of the system.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

9. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
The reporting units in this table refer entirely to colony
forming units (cfu), whereas PCR sample results are
returned in genomic units (GU). Therefore, if we get a
negative culture test but a positive PCR test – what
action to take? Or similarly, if PCR is used in isolation at
what point do you start spending large amounts of
money disinfecting water systems and taking services
out of action? There is no way of correlating the two
units and no set levels for genomic units.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

10. Nemco Utilities Limited
Legionella Sampling
Culture v PCR
Currently a large number of companies offering PCR,
back up the results with a culture test (at extra cost). It is
certainly in no doubt that future analysis will move
towards PCR (molecular photocopying as it is
sometimes known). In the meantime, we will be looking
to the HSE for guidance on the newly UKAS accredited
PCR testing method.
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk

11. Nemco Utilities Limited
Contact Details
Address Email:
Nemco Utilities Ltd  info@nemco-
12 Kempson Way utilities.co.uk
Hillside Business Park  sales@nemco-
Bury St Edmunds utilities.co.uk
Suffolk  accounts@nemco-
IP32 7EA utilities.co.uk
Website:
Telephone: 01284 724503 http://www.nemco-
Fax No.: 01284 724826 utilities.co.uk/
For more information about Legionella sampling or managing the risks associated with
Legionella, please contact Nemco Utilities at www.nemco-utilities.co.uk