There is a growing popularity of rapid test kits for Legionella widely available on the market. With much marketing information on the advantages such as rapid, easy to follow, accurate and no need for a lab or equipment.

Rapid test kits consist of Lateral flow immunochromatographic assay which is a specific antibody (a protein which acts a receptor) which changes based on the presence of a chosen antigen (a biological marker) similar to a lock and key mechanism. This all occurs on an absorbent medium such as paper through capillary action. The result is fast, often in minutes.

Many are designed to detect the presence of the most notorious, Legionella pneumophila serogroup 1. Rarely making exceptions of other serogroups or species of the same bacteria family such as Legionella Longbeachae (a known pathogen found in soil and potting mix)

Ideal as a quick convenient reference, laboratory techniques are superior but currently many companies are perfecting the rapid testing technology. They are not appropriate for your whole Legionella control program as there are limitations from a legal, quality or risk management capacity. Some of the limitations are: –

• They only detect a positive or negative result so you can’t quantify Legionella numbers or highlight presence of non-specific Legionella bacteria which could help locate and reveal problems such as Legionella favourable conditions in the system. They do not discriminate between live, dead or dormant bacteria so yes you will get positive results if bacteria are present, but it leaves the results open to interpretation. Is the bacteria capable of reproducing or is it dormant? Is it just the remains of a dead bacteria killed by chlorine or temperatures over 60℃?

 

• When using a biological mechanism there is a potential of proteins becoming denatured or blocked by high or low temps, extreme pH, presence of high chlorine residuals or other oxidising biocides.

 

• They are often expensive, have a shelf life and must be stored properly.

 

• Specific for Legionella pneumophila serogroup 1 and none of the other species.

 

• Potential user error.

 

• They often rely on an antibody which reacts to proteins (antigens) on a cells surface that are unique to different species of bacteria but not foolproof as they have been known to show false positive due to other water-bourne species which may share similar proteins. They can also be interfered with by other chemicals in the environment, for example, polymeric biguanide which is found in some household products.

 

• Although these tests have undergo excellent quality systems such as ISO 9001. Many of these tests are not endorsed by accrediting bodies.

 

• Results gathered are purely qualitative and should not be used as evidence of a comprehensive control program.

 

So when choosing these rapid kits for testing it is worth remembering why and how they are used because they are not a one size fits all solution for all situations and certainly do not replace accurate and comprehensive laboratory techniques.