The Traditional Method
When it comes to different types of Legionella testing, this long-established method of culturing the bacteria remains the ‘gold standard’ of analysis. Since it detects all species of the legionella family, additional tests can determine whether the strain found is one of the most pathogenic varieties. Pathogenic strains pose a greater risk to health.
- Detects only viable bacteria (those capable of reproducing).
- Detects all Legionella species.
- Results typically reported in colony forming units (cfu) per volume, limit of detection (tLOD) is 10 cfu/L on a 1 litre sample.
- Yields isolate for additional characterization
- Incubation takes 10 days
- Requires skilled technicians to follow laboratory method statement
- Better for evaluating growth trends
PCR Method
Polymerase Chain Reaction testing is a molecular biology technique in which the DNA of a microorganism is extracted and then amplified. Since the result includes both dead and alive legionella, it is difficult to determine what risk is posed to human health.
In extensive water systems (e.g. large hospitals), PCR tests can quickly help determine if legionella contamination is contained to a single area/ward or is widespread throughout the establishment.
- Detects Legionella-specific DNA or RNA.
- Does not differentiate between live and dead bacteria.
- Results typically reported in genomic units (GU) which are not directly equivalent to cfu.
- Rapid analysis takes just 2–48 hours to get a result.
- Is useful for negative screening.
- Good at evaluating whether remedial actions are successful.
Conclusion
It’s great that there are two types of Legionella testing methods and they have different benefits.
For most situations where you are testing (and expecting no legionella), the traditional culture method is the best choice.
If you have a known problem with legionella contamination, then PCR can be a very useful method of monitoring the success of the actions taken to reduce/eliminate the bacteria.
What new methods are being developed?
Antigen Testing
We all remember the lateral flow tests we all did during COVID, the same technology can detect legionella bacteria. This sounds great, a simple test that gives a result in a few minutes – but there are still a few technical issues to resolve yet.
- At present the sample preparation prior to dripping onto the cassette is long winded. It needs to be simplified so users don’t require training to accomplish it.
- Current technology is sensitive to Legionella pneumophila serogroup 1. An improvement would ideally show the other major pathogenic strains which can cause fatalities.
- The test can’t easily determine any difference between living or dead legionella bacteria.
Once these downsides are improved, this technology will transform legionella testing completely.
Want to stay ahead of the curve or need support with Legionella risk management? Contact Aquacert to discuss testing solutions, compliance support, and how we can help keep your systems safe.