Dip slides for legionella testing

Sep 2, 2018

The legionellaceae family of bacteria can be found in aquatic environments / artificial Water systems such as:

  • Cooling towers
  • Cooling systems
  • Hot water tanks
  • Fountains
  • Piped water systems for hotels and ships
  • Spas / hot tubs, swimming pools
  • Showers
  • Soil / compost
  • Anywhere where water is stored or circulated

The testing for Legionella should always be conducted using a Legionella specific test (dipslides do not specfically test for legionella bacteria). Therefore, you cannot use dipslides alone to monitor your water. However, dipslides can be used to assess the 'general health' of your water and will indicate if any bacteria is present.

Dipslides will monitor the total aerobic bacteria count in your system. If bacteria is present, we suggest that you conduct further tests to see if Legionella is one of the organisms in the system. Even if legionella is not identified, the presence of other organisms can support legionella by producing the organic nutrients that it needs to thrive.

Contaminants can also corrode and damage equipment / systems such as pipes which can affect the flow of water making it ideal for legionella to grow. This is why it is highly recommended that you test for all bacteria and keep all contaminants under control.

The HSE (Health and Safety Executive) recommend weekly testing with dipslides as well as routine sampling for legionella (at least quarterly). This would need to be done more frequently if the dipslides show results of aerobic bacteria.

If the dipslide aerobic count is 10,000 cfu / ml or less, this is considered under control by the HSE (UK regulations). If between 10,000 and 100,000 cfu / ml, a review will need to be put in place. Re-sampling by dipslide should also be done to re-confirm findings. It is our view, that it would be advisable to also conduct a legionella sampling at this point.

If over 100,000, immediate corrective action is required. When testing for legionella, always adhere to and research local laws, requirements and regulations.

Weekly dipslide tests

CONDUCTING WEEKLY DIPSLIDE TESTS

When testing your system with dipslides, collect first draw water in a sample as this will assist in providing a more accurate result (as opposed to swabbing). Once you have obtained your sample, you can do the following:

  • Remove the dipslide from its container and dip in to the sample.
  • Remove the slide from the sample and allow fluid to drain.
  • Replace the dipslide within its container and replace the cap.
  • Incubate the slide in a dipslide incubator (link to incubators) for 24 - 48 hours.
  • Assess your results based on the recommended safe / unsafe levels of cfu / ml in your country.

OTHER PRECAUTIONS THAT CAN BE TAKEN

  • Control any water spray. Those infected with Legionnaires disease are most commonly exposed to legionella by breathing in contaminated mist /drops of vapour /spray.
  • Keep a clean and well maintained system
  • Keep stable water temperatures that don't encourage growth. The recommended temperature for water storage is below 20 degrees celcius. Legionella bacteria can survive at low temperatures but will not grow.
  • Hot water needs to ideally be maintained above 50 degrees celcius. High temperatures (especially over 60 degrees celcius) will kill the bacteria. Growth of legionella bacteria occurs between 20 and 45 degrees celcius.
  • Insulate pipework and cisterns
  • Refurbish tanks and systems regularly
  • Don't allow water to stagnate

References and more information:
hse.co.uk
who.int

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