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Legionella Sampling

Legionella analysis is a specific test for the Legionella bacteria which should be conducted in a UKAS accredited Laboratory.

Legionella results include Presence or Absence and can include detection of Legionella pneumophila, Legionella species and usually includes sub typing to Serogroup and count expressed as Legionella count as Colony Forming Units/Litre (cfu/l).

Legionella has traditionally be cultured using culturing techniques and this is currently most economic but can take up to 10-14 days for results to be confirmed.

Rapid Legionella analysis using PCI techniques are now available via UKAS accredited laboratories and can provide Legionella analysis results with 24 hours (from time analysis commences).

Absence of the bacteria does not indicate conditions are satisfactory and complacency should not be allowed to set in and precautionary measures must be fully maintained to comply with L 8.

Action to be taken in the event of the bacteria being detected is guided by L 8


L8 Legionella Sampling In Domestic Systems – Action Requirements

L8 (Legionnaires’ disease the control of Legionella bacteria in water systems) provides clear direction regarding the action to be carried out in the event of unsatisfactory bacterial results.

L8 action levels are as follows:

Legionella Bacteria 100 – 1000 cfu/litre


  1. 1. 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.
  2. 2. If the majority of samples 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.

Legionella Bacteria > 1000 cfu/litre

The system should be re-sampled and an immediate review of control measures and risk assessment carried out to identify any remedial actions, including possible disinfection of the system.


The situation can arise where samples do not detect presence of Legionella, however plant conditions are such that, if colonised proliferation can occur. In such situations there is a potential for complacency.

Satisfactory results do not indicate that it is safe to reduce precautions.

For more information regarding Legionella or other bacterial sampling contact us.