Lessons from the history of Legionnaires’ disease 4: Legionella testing is not infallible.

In August 2017 two civilian workers at an army medical centre in USA caught Legionnaires’ disease. They both worked in the same administration building. The building was evacuated, and a programme of cleaning and inspection was undertaken. All water lines were flushed, and water heaters drained. HVAC systems were inspected and cleaned.

Tests for legionella taken pre-clean came back negative.

In February 2018 a third employee working in the same building contracted Legionnaires’ disease and the building was evacuated for a second time.

The latest testing showed that the bacteria that causes Legionnaires’ disease was present in a hot water heater.

This example shows that you should never relax in managing Legionella. There are several scenarios that could explain the above:

  1. Legionella is not homogenously spread throughout water, so the first samples could have just not had Legionella in it though the system contained Legionella, after all it is normally only a one litre sample taken from many hundreds or even thousands of litres in the system.
  2. The Legionella in August 2017 may have been sessile bacteria rather than planktonic bacteria, that means they may have been in a biofilm somewhere that the samples did not capture. The clean may then have released the bacteria into the water which were captured in February 2018.
  3. There may have been no Legionella at all in August 2017, but the incoming mains water may have introduced the Legionella bacteria in the meantime.
  4. The samples taken in August 2017 may have not been taken from the correct locations or transported correctly which meant the results were invalid.
  5. And there may be other reasons!

As can be seen there are numerous possible explanations for this example, so it is important to have the correct technical support when you manage Legionella.

A sampling plan is a good idea when embarking on sampling for Legionella as this can help you identify the best locations to sample, the guidance normally suggests you look in the most likely places as you want to ensure you capture the bacteria.

Cleaning and disinfection should be carried out to the right standard, in the UK there are several possible standards you could choose!

The risk assessment that you carry out on site should identify the areas of risk for your site and then lead to the correct control measures but how do you know these tasks have been carried out to the right standards.

Collaton Consultancy Limited are Legionella experts that can help you set up the right processes and standards for the work carried out on site. We can support you by helping you to choose the right sub-contractors to meet the needs of your site. We can also offer training to your staff, or that of the water hygiene supplier to ensure that all staff involved in managing Legionella are competent to carry out their tasks safely and to help control Legionella on your site.

If you need any help with these subjects contact Collaton Consultancy on general@collatonconsultancy.com or phone on +44(0)7958 124563.

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