If you are working in healthcare, the food manufacturing industry or any other industry where the standard of hygiene and cleanliness is of critical importance, then there is a compelling imperative to measure and assess the efficiency and the efficacy of your cleaning, sanitation and disinfection procedures. However, as with any form of diagnosis, you need to apply the right diagnostic test to yield a meaningful result that can provide the unequivocal data required to make a truly informed appraisal.
Unfortunately, in the world of cleaning, sanitation, disinfection and sterilization there is a propensity for the manufacturers of basic hygiene testing and assay tests to use unscrupulous marketing and sales techniques to sell their products as a universal panacea, a one-size fits all test kit for every diagnostic need. It is literally unfortunate because misunderstanding this subject and then using a test unsuitable for providing reliable diagnostic test results can have very hazardous consequences, to use the medical metaphor, it can lead to either a “missed diagnosis or a mis-diagnosis”.
Therefore, it is essential to understand the different levels of hygiene and cleanliness and then how to test if those desired levels are being achieved.
Levels of Hygiene and Cleanliness
In the language of cleaning, hygiene and infection control, there are basically three different technical terms assigned to define three different levels of surface hygiene. Each of these levels of hygiene are achieved in different ways with each level being a progressively more stringent level of hygiene as you move up the scale from one to three. The three levels are:
- Sanitation is achieved by decontamination and cleaning with detergents with mild degree of antimicrobial destruction and is expected to have a 99.9% efficacy rate meaning that 99.9% of all known germs will be eliminated, this is also termed as a 3-log Kill Rate.
- Disinfection has a higher level of microbial destruction with a 99.99% efficacy or 4-log Kill Rate. This level of hygiene is achieved with blend of detergents and strong disinfectants.
- Sterilisation requires an even higher level of antimicrobial destruction 99.9999% efficacy and a much higher 6-log Kill Rate which, by microbiological definition is therefore “Sterile”. This ultimate level of hygiene is extremely difficult to achieve without specialist equipment and techniques.
Testing for Different Levels of Hygiene and Cleanliness
As one might expect, the diagnostics for these three levels of hygiene require different levels of sensitivity and accuracy to effectively discriminate on the levels of hygiene being achieved. The three methodologies recommended are as follows:
Testing for Effective Sanitation
The most commonly adopted method for testing sanitation levels is ATP. It has this name as it is based on measuring Adenosine Tri Phosphate. ATP is an indicator molecule for the biological and organic residues to test surface hygiene. The ATP methodology has been used for surface hygiene monitoring immediately after sanitising has been completed to check its efficacy.
ATP is an indicator molecule for the presence of biological residues. ATP testing solutions work by capturing the molecules from a surface or water sample via a swab. To measure ATP, the sample is mixed with an enzyme from fireflies called luciferase, which catalyses a reaction where two of the phosphates are broken off from the ATP molecule. The energy from this reaction is captured by the enzyme to create light.
The swab is then inserted into a device called a luminometer, which reads the amount of light produced by the sample. The light produced is proportional to the amount of ATP in it: the more organic residue on the surface, the more ATP; the more ATP, the more light produced. The light is detected in an instrument and displayed in relative light units, or RLUs. The higher the RLUs, the more likely it is that the surface has not been properly cleaned.
ATP testing is a well-established method for measuring hygiene; however, it cannot be used as a replacement for traditional microbiology tests and is therefore not appropriate for definitively measuring the efficacy of disinfection or sterilisation. ATP tests detect ATP from all living cells and organic residues, so it is not inherently indicative of the measure of bacteria on a surface. RLUs measure the overall cleanliness of a surface rather than the number of bacteria. If you want to measure the numbers of bacteria on a surface, then you use a well-established microbiological method and measure the number of colony forming units (CFU) per area of the surface being tested.
Because colony counts and RLU values are determined using different test methods and measure different elements of hygiene, RLU values DO NOT correlate to colony forming units when testing an environmental surface.
Testing for Effective Disinfection
If one is concerned with the level of disinfection being achieved (i.e. a 99.99% microbial kill rate) then the only accurate methodology is to check for CFU’s ‘pre and post disinfection’. This involves carefully swabbing a pre-determined area and then incubating the viable bacteria harvested from the surface and actually counting their numbers. This is the only definitive method to determine a pre and post disinfection efficacy rate or in microbiological terms, the log kill rate which in the case of disinfection would need to be 99.99% or more.
Testing for Effective Sterilisation
If one is concerned with the level of sterilisation being achieved (i.e. a 99.9999% microbial kill rate) you are in essence checking for the absence of microorganisms rather than their presence.
Therefore, checking for CFU’s ‘pre and post sterilisation’ can also be an effective methodology but swabbing larger areas as you are seeking evidence of much smaller numbers of viable bacteria, if indeed any. Once again this involves carefully swabbing and then incubating the bacteria harvested from the surface and actually counting their numbers. This is the only definitive method to determine a pre and post sterilisation efficacy rate or in microbiological terms, the log kill rate which in the case of sterilisation would need to be 99.9999% or more. In practical terms this equates to the total elimination of all viable bacteria.
The conclusion here is very simple, use the appropriate level and type of testing based on what you are actually trying to determine.
- If you are trying to assess whether a surface is merely clean or dirty and want to go beyond visual inspection, the ATP might be the method of choice.
- If you are trying to assess either disinfection or sterilisation rates, then it can only be determined using standard microbiological methodologies such as harvesting and incubating CFU’s.
If you use the wrong test, for the wrong diagnostic you will inevitably get the wrong result!