This is the fourth in the series of articles by Dr Andrew Kemp JP PhD RGN FBICSc L/RAMC, CEO at AK Medical Ltd, looking into the world of cleaning and disinfection.
I am grateful to Birkin Cleaning Services Ltd for its sponsorship of these articles. It is probably worth mentioning that this company is, in my view, at the absolute cutting edge of cleaning technologies and practices.

Which is best, persistent or non-persistent disinfecting technology?
The vast majority of disinfectants in use today have limited contact time (the time a disinfectant is active and in direct contact with the surface or item to be disinfected). The kill time (the time a disinfectant takes to kill an organism) must not exceed the contact time, or the disinfectant will not be in contact with the organism long enough to kill it. Different disinfecting chemistries have different contact times and kill times. It is important for cleaning operatives and supervisors, to know the properties of the chemicals they are using, to ensure they are providing the correct levels of cleaning and disinfection required for each area they are responsible for.
Standard test methods accepted by regulators, and approved by BSI/ISO (among others), use 30 secs, 1min, and 5 mins after contact, as the time periods to measure efficacy of a disinfectant or hand sanitiser. The reasoning behind these times, is that most non persistent disinfectants have a contact time of between 3 and 5 mins. If you read my last article about potential corruption in regulatory bodies, you will understand why I believe that these times were in fact set by the chemical industry, not the regulators, and why it is rare that anyone tests over longer periods than 5 mins. To be considered effective as a disinfectant, a chemical will need to achieve a “log 4 or 5 reduction”. That means that five minutes after exposure to a disinfectant, 99.99% to 99.999% of the bacteria will have been killed.
What is the real difference in efficacy?
Let us assume that two disinfectants have the same log 5 reduction at 5 mins exposure. One of the disinfectants is non-persistent and has a contact time of around 5 mins. The other is persistent in its action, that is to say it will continue to kill whilst it remains on a surface, the skin, or in the air, in some cases on surfaces more than 7 days. The bacteria we will use will have a kill time less than the 5 min contact time for most disinfectants.
Individual bacteria are able to reproduce. They do this at different rates depending on their species, the environment they find themselves in, and the food available to them. For the purposes of the following calculations, we will assume the bacterial species will divide into 2 every 15 mins if left unchecked, and that food is available to them.
Let us look at the basic maths:
Non persistent disinfectant
10,000,000 bacteria on a surface are subjected to the non-persistent disinfectant. After 5 mins there are just 100 left. A good result you may think. After 15 mins, there will be 200, another 15mins 400 and so on. After 4 hours and 20 mins there will be 13,107,200 live bacteria.
Persistent disinfectant
We start with the same 10,000,000 bacteria, on the same surface, and subject them to the persistent disinfectant. After 5 mins there are 100 left, after a further 5 mins there are zero left alive. Why? It is because the persistent disinfectant achieves a 99.999% reduction every 5 mins until it is either worn away or removed.
At all time periods after 5 mins, there is a clear difference between these two types of technology. However, currently most chemical industry regulators would in fact give them the same level of accreditation. As there is no doubt the difference between these results is likely to be significant in reducing cross infection, I therefore wonder why the regulators refuse to differentiate? In fact, the US EPA recently introduced a new category of disinfectants that requires testing over 24 hours, and a further category that tests over 7 days. Is the future therefore going to include a significant place for persistent technologies? I presume that however hard the chemical industry lobbyists try to stop others from doing likewise, the rest of the world will eventually follow the EPA lead.
We now have proof positive (as yet unpublished) that surface microbial contamination levels affect the microbial contamination levels in the air, and vice versa. Whilst there are multiple persistent products available in the US that are not available here, two new products using similar technology, that are safe and have persistent efficacy for both air and surface disinfection have recently become available. With the help of Birkin Cleaning Services Ltd, I was able to test their efficacy.
The new disinfecting technologies
Technology 1 – Advanced Photocatalytic Oxidation (APO)
This technology is primarily used for active reduction in live microbial activity in the air by filtering the air, whilst also producing and circulating a hydroxyl radical (free radical) anti- microbial aerosol. Until the introduction of this patented technology, in order for free radicals to effectively kill microbes in the air and on surfaces, the concentration used would have to be above the safe maximum exposure levels (MEL’s). This would mean that either significant PPE was worn in the rooms being treated, or people could not be in the room when machines were activated. However the inventors have discovered a method of reducing the concentration to well below safe MEL’s, whilst maintaining a therapeutic value. This is achieved by reducing the concentration of free radicals, then passing the air flow over titanium dioxide in the presence of UVc light. There is some, as yet unpublished evidence, that this technology has the secondary effect of reducing live microbial levels on surfaces.
Technology 2 – Photocatalytic solution
This surface treatment uses similar Photocatalytic technology to the air cleaning product, in that it uses a form of free radical as its active antimicrobial. As a persistent surface treatment, it is applied every 6 months to clean surfaces, and remains in place until worn away through frictional forces, i.e use. Like any persistent antimicrobial technology the reapplication schedule is based on the perceived levels of use of the surfaces, and may change from surface to surface. At the time of publication, a test is being developed that will show the presence of sufficient antimicrobial for it to remain therapeutic.
With both technologies, standard cleaning is recommended to be continued. Test results when both technologies are used.
Bacterial counts were taken from two busy office rooms, a control room and a room treated with the persistent disinfectant and the air cleansing system. Rooms were tested, after cleaning and before the start of the business day, and then again at the end of the business day before cleaning. Live Colony Forming Unit (CFU) counts were obtained using a hyper accurate Bacteria Specific Rapid Metabolic Assay (BSRMA) test. In addition, blood agar cultures were used for species identification.
During the 48 hour testing period, the room used as the control, showed an over 500% increase in surface bacterial bio burden by the end of the working day, on both days. The treated room showed a significant reduction in CFU counts, and by day 2 no samples had grown cultures on any plates. Surface live bacteria counts were reduced to less than one CFU per cm2.
Discussion
Although this is a small scale study, the results are so compelling, there can be no doubt that the combination of these two new technologies reduces the live CFU counts and therefore will reduce the risk of cross infection from surfaces and in the air.
It is clear there is more research required if we are to determine which of the new technologies is most efficacious on surface contamination levels, and what is the effect on air contamination. It is possible that due to the “Holism theory” or “Entourage theory” both products may have similar or equal efficacy, or that their individual efficacy is increased by the combined use with the other product. It is also unclear as to how much effect the reduction in live CFU surface counts will have on staff sickness. For the moment, if given the choice, I would wish to work in an office where both technologies are in use.
We must now undertake further studies to answer these important questions.
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